Tom Saxton's Blog

Leaf SOC-Meter Build Party

2012-01-23T05:44:14Z

Nissan did a great job with the Leaf, but I do have one gripe: the lack of a state-of-charge meter with enough precision that you can understand how much energy you use and how driving conditions affect efficiency. Having a good SOC meter allows drivers to comfortably use more of the car's range.

Fortunately, there's a strong Leaf community with a lot of smart owners. Generous owners have spent probably thousands of hours decoding the messages available through the Leaf's on board diagnostics (ODB) port, creating software to interpret those messages, and designing hardware to view and log this information conveniently.

About a month ago, I realized my efforts to build a gizmo and contribute to the community effort were stalled while I worked on other projects, so I suggested we buy one of GaryGid's SOC-Meter kits. As long as we were doing it, I thought it would be fun to invite other owners in the area to do a group order.

Cathy liked the idea and organized the purchase and a build party. We got enough interest to order 10 kits, which arrived in time for Cathy to build our meter in advance so she understood the assembly and could help everyone with the build. In addition, she updated the build manual and added photos.

We arranged to meet at a local Maker space, StudentRND, in Bellevue. It's a great shop, with lots of room to work and cool tools like a laser cutter. If you're in the area, we recommend checking them out.

We met on Saturday. Despite the inclement weather (we had to shovel two inches of mostly ice from our steep 500-foot drive to get our Leaf on the road), we had a good turnout. Here's a photo Cathy took early in the process:

A little later, there was more going on as people made progress on their kits. I'm in the back of the photo, working on my iPhone program for logging EV data.

The only barrier to getting the assembly done in a couple of hours is letting the silicone adhesive cure for an hour in the middle of the process. Still, we had a couple of folks finish and test their meters during the meeting. Cathy is putting the finishing touches on an update to the assembly manual with some insights she learned from the party.

The final product is pictured below, including labels that Cathy added to the kits for our build group.

We now have our meter fully installed in the car. It's awesome.

Watt Fun: Driving a Nissan Leaf

2012-01-17T01:58:28Z

In September, we finally got our Nissan Leaf. We had signed up very early in the process, and could have had a Leaf in the spring of 2011, but we decided to put our order on hold until they offered the cold weather package. It was worth the wait!

It's now our primary vehicle and we've put just over 2,000 miles on the odometer. Here's our review of the experience so far.

The Good

Driving Experience We've been driving electric since 2008, so it's easy for us to forget how much better the driving experience is with an electric drive train. The accelerator pedal on the Leaf gives instant, smooth response: you push, it takes off. There's no waiting for a gear shift, and no slow climb to full acceleration the way you have to wait for a gas car to rev up the engine speed to maximum torque, then have to shift gears and repeat. It's just smooth, rapid acceleration all the way. I'm sadly reminded of this every time I fly somewhere and am forced to rent a clunky gas-burner.

Braking The Leaf also features regenerative braking. In a gas car, if you want to slow down you have to hit the brakes. This costs you money twice: you're throwing away the kinetic energy of the car and you're wearing out your brake pads. With regenerative braking, you use the motor as a generator to slow the car and charge the battery pack, plus you avoid wearing out the brakes. Even more than the cost savings, regenerative braking shines when going down a hill. In a gas car, you have to ride the brakes or downshift. Riding the brakes is bad as it heats up the pads and can present a safety issues on long downslopes. Downshifting, or engine braking, is better except that you have to chose one of a few gears. With regenerative braking, you can smoothly control your speed with your right foot, whether you're accelerating up to speed, or holding your speed going downhill. Friction brakes work just as on a gas car when you need to stop quickly.

Controls The Leaf has a built-in touch screen for controlling the navigation system and the audio system (AM, FM, CD, iPod/MP3 player, and the ability to subscribe to satellite radio), as well as viewing car information and setting preferences. There are tactile controls on the steering wheel for the audio system and cruise control, and tactile controls around the touchscreen so you can control the vital systems by touch without taking your eyes off the road.

Backup Camera The 2011 Leaf SL package adds a backup camera displayed on the large center console screen. With the camera, it's so much easier to back up whether it's out of a parking spot in a crowded lot, backing into a spot, or just being able to back up against an edge or wall when getting out of a tight spot. I'm now spoiled and miss this feature when driving a car that doesn't have it.

Touchless Keyless Entry The Leaf detects the keyfob wirelessly so that when you are right next to the car, you can just push a button on the handle to lock or unlock the doors or the hatch. You don't have to fumble to pull your keys out of your pocket or purse, which is incredibly handy when you have an armload of groceries. It's the same for starting the car, no fooling with a key, you just push a button and the car starts as long as the fob is inside the car with you. The car knows the location of the keyfob with enough precision that it won't let you lock the keys in the car and can warn you with a beep if you get out of the car without turning it off.

Quiet Ride It's widely reported that electric cars are quiet; some even wrongly claim they are silent. Electric cars don't have noisy internal combustion engines that have to be muffled. At low speeds they can be surprisingly quiet, although you quickly learn to recognize their unique sound even when they creep up slowly behind you. At speeds above 20 mph or so, they make the same noise as a typical gas car does, which consists mostly of tire noise.

That's the story outside the car. Inside the car, it's tricky to do a good job of insulating road noise while keeping the vehicle weight low to maximize efficiency and range. Even if you get rid of the dominant road noise, you just make it possible to hear all sorts of little sounds that you wouldn't notice in a less insulated car. This is especially difficult when there's no engine noise to mask other drivetrain noises. This is the reason for the Leaf's unusual protruding headlights: they deflect airflow around the side view mirrors to get rid of a wind noise you wouldn't even notice in a noisy gas car.

Our two other electric vehicles sound just like the Leaf from the outside, but inside the Leaf is a completely different experience, by far the quietest riding car we've ever owned. I haven't seen the data, but I suspect it's on par with heavily sound engineered luxury sedans that cost far more than the Leaf.

Cold Weather Comfort Because the Leaf uses electric power to heat the car, it doesn't have to wait for an engine to heat up before it can start blowing warm air. The cold weather package (now a standard feature on the 2012 Leaf) adds heated seats (front and rear), heated side mirrors, and a heated steering wheel. If you're driving in the cold, there's nothing more wonderfully decadent than a heated steering wheel. With the cold weather package, the heated seats and the steering wheel get warm even faster than the cabin air.

The cold weather package also adds a battery heater for really cold climates. That's not an issue in Seattle where we rarely see temperatures below 20°F, but is important in more extreme climates.

Remote Control and Monitoring Using a wireless communications system called Carwings, we can monitor the car remotely to check things like the state of charge. The system sends us a text message if we pull into the garage but forget to plug in.

We can also tell the car to pre-heat from our phones. This is something that just can't be done with a gas car sitting in your garage where running the engine would fill the garage, and possibly the house, with deadly carbon monoxide. If the car is plugged in, it uses grid power for the pre-heating, so it doesn't reduce our range. Most of the time, our driving is nowhere near any concern about range, so we use the pre-heat feature even when it uses battery power to warm the car for our return after it has been sitting in a cold parking lot.

Fuel Cost At the US average cost for electricity (11 cents per kWh), the Leaf can drive 30 to 35 miles per dollar of electricity. If gas costs $4/gallon, that's the equivalent of getting about 130 miles per gallon, not in a gutless, rattling economy box, but in a quiet, comfortable car with excellent acceleration.

If the savings in fuel cost is applied to a buyer's monthly car payment, the Leaf is an incredibly affordable car.

Convenient Fueling The Leaf is best suited for local driving, which fortunately accounts for more than 90% of the typical American's driving. If you can use the Leaf for your local driving, you'll find plugging in overnight to be far more convenient than going to a gas station. Especially if you share a car, you've no doubt experienced the rude surprise of needing to make a detour to a gas station, spend time waiting in line, and pump gas when you're already running late. The Leaf is fully charged every morning with just a few seconds of effort required to plug it in at night, about as much time as it takes to plug in a cell phone. Charge time varies with how far you've driven, anywhere from a few minutes to eight hours, but it doesn't matter at all because it happens while you're sleeping.

I know many people think charging time will be an issue, but I just laugh when I see people waiting in a 20-minute line to save a few pennies per gallon at Costco. Driving electric, I pay the equivalent of $0.99 per gallon of gasoline and fueling takes just a few seconds of my time per day. I can only imagine how long the line would be if Costco sold gas for $0.99 per gallon. I get that price and I can charge up in my garage where there's always shelter from the elements and never a wait.

The Bad

Nissan has done an amazing job with their first full production electric vehicle. It's the most comfortable car Cathy and I have ever owned. It's a wonderful car, with no competition whatsoever at any price when considering the comfort and convenience it offers plus the liberation of not being hostage to wildly fluctuating gas prices. However, Nissan got it wrong on two important aspects of driving electric. The good news is that new electric vehicle drivers will get all of the benefits mentioned previously before they notice these more subtle shortcomings.

Increasing Range Anxiety Range anxiety is the irrational fear of running out of power even when an electric car has plenty of range for your driving needs. The way the Leaf presents information about the car's state of charge causes range anxiety. The dash shows in large numbers an estimate of your remaining range. That sounds pretty reasonable, but it has to make an assumption about how you will be driving for the rest of the trip. The Leaf assumes you'll be driving the same as you have been for some unknown period of time. Unless you do all of your driving under exactly the same conditions, same steady speed and constant slope, that estimate is going to be wrong pretty much all the time since it fluctuates wildly as conditions change.

The best information we get is a 12-segment display that displays the state of charge in approximately 8% increments. The problem is you can't tell where you are in the bar. Suppose I drive from work to the grocery store and the gauge drops from 8 bars to 6 bars. That could be from the top of bar 8 to the bottom of bar 6 (almost three bars, or 24%) or from the bottom of bar 8 to the top of bar 6 (just over one bar, or 8%). That's a big difference.

While the estimated range can be useful in some circumstances, Nissan should give us a way to display the car's state of charge as a percentage. I understand that there is some inherent uncertainty in computing the precise amount of energy remaining, but the raw state of charge should be presented to the driver with the same precision as the estimated miles. Having this information would help drivers better understand their energy use and increase the Leaf's usable range. This is such an important piece of information that owners have figured out a way to display the state of charge by tapping into the Leaf's on-board diagnostic port.

Denying the Best Feature of Electric Driving The regenerative braking offered by an electric car dramatically improves the driving experience. Once you get feel of driving electric, it's a joy be able to control your speed with just one pedal: push down to speed up, lift to slow down. Whether it's uphill or downhill, speeding up an on ramp or slowing down for an exit, you do it all with the accelerator pedal. It's far more natural than how it works on a gas car, it's just different from how we all learned to drive. Nissan was apparently concerned about making the Leaf feel as much like a gas car as possible so as not to scare away consumers afraid of change. To do this, they have two modes, normal and economy mode. In normal mode, there's a limited amount of regenerative braking on the the right pedal. In economy mode, there's more regenerative braking, but acceleration is dampened out. You can get the same acceleration in eco mode as normal mode, you just have to push the pedal farther down.

I want maximum regenerative braking, so I always drive in eco-mode. This makes the accelerator less responsive unless I really push it. I would much prefer a more typical pedal response with the maximum regenerative braking. It's also annoying that the drive mode doesn't persist, I have to put it into eco-mode every time I start driving.

Conclusion

Nissan clearly leveraged what they learned from making the world's first factory-made lithium-ion electric car over ten years ago* to create an incredible first generation production electric vehicle.

The comfort features of the Leaf make it worth the sticker price, even if it had a gas drive train. With efficiency that can't be matched by an internal combustion engine and fueled with cheap domestic electricity, the savings in total cost of owning and driving the Leaf make it the uncontested winner in value for its class of comfort and driving experience, in many ways superior to all gas-powered cars at any price. Add in the environmental benefits and the satisfaction of knowing your fuel dollars stay in the US instead of pouring into the global oil market that threatens our national security as well as our economy, and no other car on the market offers the value of the Nissan Leaf.

If you're in the market for a new car, and typically drive under 60 miles per day, and already own a gas car that you can use for those few longer trips, you owe it to yourself to test drive a Nissan Leaf before investing in another gas car.

* The all-electric Nissan Altra built to satisfy California's short-lived zero-emissions mandate from 1997 to 2003.

Tesla Roadster Battery Capacity Over Time and Miles

2011-12-20T05:19:36Z

Tesla Motors was the first automaker to sell a production electric vehicle based on lithium ion batteries, the Tesla Roadster. Current Roadster owners as well as other prospective electric vehicle owners are interested to know how these batteries will hold up over time and miles.

It's still pretty early in the game. Tesla Motors tells us that we should expect to have our battery packs holding 70% of their original capacity after 5 years or 100,000 miles. The oldest Roadsters are a bit over three years old and some vehicles are getting up into the 30,000+ mile range.

How are the battery packs holding up so far? I've collected data from 20 owners in the Pacific Northwest to get an approximate idea of our batteries are performing.

Before we dive into the results, I should explain a bit about how battery capacity is instrumented on the Roadster. The Roadster has two primary charging modes. Standard mode charges up to about 90% of the pack's capacity and holds the bottom 10% of the capacity in reserve. Range mode fully charges the battery pack and shows the full range available, including the bottom 10%. The range is shown in two ways, "Ideal Range" and "Estimated Range." Estimated range states the range based on recent driving history and so can't be compared across vehicles. Ideal range shows how many miles you can drive in the current mode if driving with the same mixed city/highway average energy use that gave the Roadster its EPA -rated 245 mile single charge range. The corresponds, for example, to driving 55 to 60 mph on level freeway in moderate weather.

First, let's see how miles driven affects battery capacity.

The red squares at the top of the graph show the range mode capacity expressed in ideal range miles (aka ideal miles) versus miles driven on each battery pack. The blue diamonds show the standard mode range. The straight lines show the tread for each set of readings. I interpret this graph to show that for this set of vehicles, individual variation between cars is larger than the pack degradation over approximately 30,000 miles. For range mode, the variation between cars is as much as 15 ideal miles between cars with comparable mileage, while the linear trend shows a drop of only 5 ideal miles across 30,000 miles of driving. For standard mode, the variation between cars of comparable mileage is under 10 ideal miles while the trend line shows a drop of perhaps 6 ideal miles.

Lithium ion batteries lose capacity over time even if you don't use them. The graph shows the same vehicles over time instead of miles.

Again, we see the same apparent patterns: variation between vehicles is larger than the average range lost over three years and variation in range mode is larger than the variation standard mode.

While this is enough data to see some patterns emerge, it's a small fraction (about 1%) of the total Roadsters on the road. I'd like to collect more data to confirm these trends and also separate the effects of time and miles. Most of the Roadsters in this set are in the relatively mild coastal climate of Oregon, Washington and British Columbia. It would be interesting to analyze data from Roadsters in more extreme climates.

Steve Jobs - 30 Years of Life-Changing Influence

2011-10-06T16:05:26Z

In 1983, I was a math grad student at the University of Utah. I was a student representative on an administrative committee and heard about a top secret Apple demo where they had been shown a new computer that "looked like it was something out of Star Wars." The next year, every department at the university got two Macintosh computers with 128 KB of RAM, a 400 KB floppy drive, an 8 MHz CPU, and a 512x342 black and white screen.

This was cutting edge, state-of-the art computing, something that, back then, looked like it was straight out of science fiction, and one of them landed in the grad student lounge where we could figure out what it meant.

I'd been programming since junior high, first on a programmable HP calculator, then in BASIC on an Apple ][ in high school. I only took one programming class in college, "Introduction to Programming in Pascal" my freshman year. I narrowly missed having to use punch cards for that class because I had a computer account on the math department mainframe. Over the years, I did a fair amount of programming, it was a useful tool for solving math problems, which I got plenty of as a dual major in math and physics. All of that programming was console stuff: log in via a dumb terminal, edit program files in a very nerdy text editor, compile and run to get results back as lines of text. You could make the output pretty by carefully using spaces to make columns line up, maybe even draw awesome graphs by printing out spaces and x's in just the right spots.

The Macintosh was a completely different beast. It had a graphical interface that used images to convey information. It was easier to use and you could do things that were unimaginable on the terminal to the main frame. In 1985, I bought a Mac 512, the next generation with 4 times as much memory. Later, I took a year off from grad school to work for the University of Maryland, European division, teaching math and computer science to American military personnel on the air force base in Inçirlik, Turkey. I bought a custom-fit bag for my Mac 512 and hauled it across Europe to Turkey, bought copies of the Inside Macintosh programming reference books and taught myself C. I hacked the startup screen that said "Welcome to Macintosh" to say "Have Mac, Will Travel" instead.

I nearly got trapped in Turkey because of the Mac. Turkey carefully controlled technology imports, so if you brought a computer into the country, it got marked in your passport. When you left, you had to take the computer with you or pay an astronomical tax, like three times the cost of the computer, a fortune to me. I took a brief trip to Germany to deal with an eye issue, and took the Mac with me (of course), but because it was a weird military flight, the Mac didn't get marked as leaving. So, when I came back I got a second Mac added to my passport! The customs guy who was trying to explain the mess I was in through an insurmountable language barrier finally made a gesture indicating handcuffs, me, and Turkish prison. That got my full attention. Fortunately, I was able to resolve the issue with the head customs guy over tea arranged by a fortunate contact, a Turk who taught Turkish classes on base.

After that year, I got back to school, but was stalled choosing a thesis topic for the PhD program, at least partly because I was spending all of my spare time programming the Mac. I wrote a program that let you type in an equation and it would graph it on the screen. It was a pretty basic idea, but there wasn't a Mac program that would do that, at least not one that didn't cost a fortune. A publishing company licensed it to include with the teacher's edition of a math text book and I got my first paycheck for writing software. That summer, I got a job with a small local Mac software company. It was almost a real job, paying real money and I had fun doing it. That was a big revelation: people would pay me to do something I enjoyed. Suddenly, getting a PhD in math so I could maybe get a job teaching math wasn't as interesting.

That summer, 1987, I applied for jobs at companies I admired, Quark for their awesome desktop publishing app, and Microsoft for Word. I got the job at Microsoft working on the Mac version of Word.

By then Steve Jobs had been ousted from Apple. The momentum of Steve's vision carried the company for a few years, but eventually there was a series of uninspired CEOs overseeing the production of a complex array of boring beige boxes while the operating system made slow progress moving forward.

By the mid-1990s, Apple was struggling while Microsoft was rapidly growing. With broad success on Windows, Microsoft's interest in Mac products waned. It became increasingly difficult to work on Mac products without spending incredible amounts of energy advocating for something better than getting the Windows version to run on the Mac. I stuck with it for several years after it became the opposite of fun, partly for fear that if the Mac version of the Office apps died, so would Apple.

During those years, I met Cathy, who shares many of my interests and is arguably even nerdier than I am. The attraction was (and is) strong enough that we got married even though she is an unwavering Windows user.

In 1996, Steve came back to Apple and things started to look up in the world of Mac.

In early 1998, I'd had more than enough of working at Microsoft, trying to produce a great Mac product and getting more grief and frustration than support, so I left, and Cathy followed shortly thereafter.

It took a few years, but Steve got Apple back on track, mostly by doing things that seemed crazy to me. When Steve announced the iMac in 1998, I declared it was one past the last Mac I would ever buy.* A cute-looking computer with no floppy drive, no serial port and no standard Apple mouse and keyboard connector? Instead, it had a USB connector, this crazy new thing that no other computer company was using. Insane!

In 1999, I went to the Worldwide Developer Conference. It had been a few years since I'd been and I'd lost track of the ever-changing strategy to modernize the Macintosh operating system. When Steve rejoined Apple, it was part of the deal where Apple bought what remained of NeXT. I'd seen a NeXT machine in 1998 and thought it looked beautiful and had an intriguing development environment, but the hardware was too expensive and no one was buying it. Come to find out, the latest OS strategy at Apple was to bring NeXT into the Mac, or perhaps more accurately to paint Mac of top of NeXT. They were far enough along that I could tell it was going to be cool: the elegance of the Mac user interface built on a unix-based foundation: beauty and nerdy all at once. With Apple's stock price in the toilet, I bought a modest chunk of stock at $14 per share just in case I was right and they had something good going on. (I should have bet much more. I eventually sold it the second time it got up to $200, after which it shot up over $300.)

In 2001, Steve announced the iPod, this crazy portable music player, sort of like a Sony Walkman, but with a hard drive. Lots of other companies were making things like this, and it was turning into a commodity market. The iPod looked cool, but why would I buy one? What was Steve thinking? And eye-pod? What kind of a name is that? The whole thing was embarrassing. Cathy prompted us to finally buy one, and we liked it. So did a number of other people.

In 2007, Steve introduced the first iPhone. I understood this one right away, and Cathy waited in line for me so I could buy one on the first day they were available. Steve Ballmer hilariously said, "There's no chance that the iPhone is going to get any significant market share. No chance."

Now I carry a computer in my pocket with a 1 GHz processor, 512 MB of RAM, 32 GB of storage, and a 640x960 full color screen. It's connected to the Internet from nearly everywhere on the planet within 20 miles of a traffic light. It also happens to make phone calls.

I'm now back where I was in grad school, spending all of my spare time programming on projects I find interesting, mostly on the iPhone these days. Occasionally, I get paid for my programming work but most of the time I just do it to make doing some task easier or more enjoyable.

It took the work of tens of thousands, if not millions, of people to make technology advance this far in 30 years, with a lot of it fueled by the competition between Apple and Microsoft. Perhaps Steve didn't do much of the technical work, but he saw what could be done years ahead of everyone else and pushed things in the right direction at Apple, NeXT and Pixar. It's been a blast riding the wave of advancements he inspired and worked so hard to realize. I never met him in person, but I saw him speak many times at WWDC and the Macworld Expo over the years. It's been an honor to live through the Steve Jobs age. I'm sad to see it over way too soon, although I'm sure his influence and vision will carry forward for many more years.

* That's a very nerdy joke making a play on the Hungarian naming convention, a powerful programming technique invented by Charles Simonyi, with whom I had the privilege of working on Mac Word during my first several years at Microsoft.

Where Do You Gas Those Things Up?

2011-09-05T15:30:00Z

updated 9/6/2011 2:42 pm: added nerdy charge graph

Last week, Cathy and I took the Roadster for a car show and week of island hopping through Washington's San Juan Islands and Vancouver Island in British Columbia. It was a lovely trip and unique in our EV road trip experiences in that we did the entire 450-mile trip using only 120V charging.

We are frequently asked where we charge our electric cars. The question is often accompanied by a pained expression that tries to offer sympathy for the sacrifice we make by driving electric. The answer is: mostly at home. People are frequently surprised to learn we have found it to be more convenient than going to a gas station.

Occasionally, we take a trip that requires charging on the road. That generally requires planning and finding electric vehicle charging stations. For this trip, there were some charging stations available, but they turned out to be both overpriced and unnecessary. We had chosen B&Bs that would allow us to charge from normal household outlets. On one island this was a big help as there were two otherwise equivalent choices: one that wanted to charge us $20 to use $1.60 worth of electricity and another that said we could do it for free. We gave our business to the one that didn't think we were incapable of doing math. Since we were taking a leisurely tour, and mostly on small islands, overnight charging at 120V was plenty for our daily driving needs.

The convenience of being able to fuel up from any outlet became especially apparent when we drove past this gas station in Sooke, BC.

We were on our way to Port Renfrew, some 45 miles further west along the southern coast of Vancouver Island. Had we been in a gas car, this would have been our last chance to gas up before our return, some 90 miles for the roundtrip plus any side excursions. Because we were in an electric car, and outlets are far more common than gas stations, we didn't care.

At Port Renfrew, we were going to be staying in a yurt at the Soule Creek Lodge. We'd contacted them in advance and knew they had an outlet we could use to charge the car. Charging at 120V only yields about 3 to 5 miles of range per hour of charging, which is painfully slow if you are waiting while you charge, but totally adequate if you're sleeping through it.

Our one night there, we picked up 53 miles of range, which was plenty to get us through the next day's driving.

My only regret for the trip was not getting a photo at Wildwood Manor on San Juan Island where we had deer grazing next to our charging car. Somehow you just never see deer grazing at a gas station.

Nerdy Charge Graph

Here's a graph of our state of charge for the trip. It shows the car's range in standard mode ideal miles, which means we can go that many miles at 55 to 60 mph on the highway, with another 25 miles in reserve.

The first steep dive is the 90-mile drive to Anacortes, WA, to catch the ferry. Then there's a flat spot while we wait five hours after missing the cut-off for the unexpectedly popular first ferry by 5 minutes. Over the next three nights, we charged up overnight on Lopez and San Juan islands working back to a full standard mode (90%) charge, then a fourth charge returned us to full again. There are also a couple of little afternoon charges in there. The fifth charge is in Victoria, BC, after which the car stayed parked for a full day, then we did a range mode charge prior to departing for Port Renfrew. The overnight at Soule Creek Lodge got us back up to the top of standard mode (about 190 ideal miles). Finally, the long 170-mile drive home with a short stop for lunch then a longer stop for the ferry ride. We got home with 10 miles of range left (thanks to my heavy right foot as it became clear we had plenty of charge), plus the 25 miles in reserve. The last spike shows the steep slope of 240V/32A charging at home.

A LEAF could do a pretty similar trip. Depending on the starting point, it might need a little charging on the way to Anacortes (like spending an hour or two at a J1772 charging station at the Burlington outlet malls instead of spending five hours in the ferry line). Instead of spending two nights with a full day in Victoria (where we didn't drive or charge), spend one night in Victoria on the way out and the second night on the way back.

EV Efficiency: Tesla Roadster and Nissan LEAF Compared

2011-08-10T04:00:23Z

How do the Tesla Roadster and Nissan LEAF compare in energy use?

Tesla Roadster owners have been driving electric for a couple of years now and have built up knowledge about how much energy is required for many different routes and driving scenarios. New Nissan LEAF owners could perhaps benefit from what Roadster owners have learned, especially in the near term while charging stations are few and far between.

On August 4, 2011, we did a test to answer a couple of questions:

How does energy use in a Nissan LEAF compare to a Tesla Roadster?

Does knowing how much energy a Roadster uses for a certain drive help a LEAF owner plan the charge needed for a long drive?

The Plan

To take a first stab at figuring things out, Cathy and I joined up with her parents, Jim and Barbara Joyce, to drive a Nissan LEAF and a Tesla Roadster on an interstate freeway up a mountain pass. We wanted to compare just the two cars and eliminate as many other variables as possible. We drove up together so we had identical road and weather conditions, put the cars on cruise control to minimize driver differences, and restricted ourselves to using the fan but not air conditioning. From Roadster data collected on previous drives and also a recent LEAF drive up the same pass, we were pretty confident it could be done from the Joyces' home even cruising at 70 mph. We were right.

The Route

We started at the Joyce residence near where Washington State Highway 18 meets Interstate 90 at Exit 25. Their LEAF started with a full charge. We drove to I-90, recorded trip and energy data at the stop light at the base of the on-ramp, accelerated up to 70 mph, then locked on cruise control. We exited I-90 at Exit 52 and recorded trip and energy data at the bottom of the off-ramp. We puttered around the summit for a bit, got some lunch, then reversed the route, again recording data at the bottom of the on-ramp getting back onto I-90 and again after exiting the freeway back at exit 25.

The Results

The graphs below show energy use for both vehicles up the pass from exit 25 to 52, a distance of 27 miles with a 2,000 foot elevation gain, then the descent back down from exit 52 to exit 25.

The graph shows that the LEAF used about 6% more energy than the Roadster on the way up and about 13% more energy on the way down. Both vehicles used about twice as much energy on the way up as the way down, although that ratio depends on the slope and speed. For a sufficiently steep road and slow descent, an electric vehicle can actually gain net energy driving downhill. At 70 mph, we did not see a lot of energy production, just low energy driving. At slower speeds, more energy would have been produced on the steep sections of the descent.

The LEAF averaged 2.7 miles per kWh (376 Wh/mi) on the way up and 4.8 mi/kWh (233 Wh/mi) on the way down, for an average of 3.3 mi/kWh (305 Wh/mi).

The Roadster averaged 2.8 miles per kWh (355 Wh/mi) on the way up and 5.5 mi/kWh (206 Wh/mi) on the way down, for an average of 3.6 mi/kWh (271 Wh/mi).

How Much Charge is Needed to Drive a LEAF Up to Snoqualmie Pass?

The LEAF doesn't give an indication of the state of charge to any useful precision, so we could only measure energy use from the trip miles and miles per kWh supplied by the LEAF. In terms of how much charge we used, the LEAF started with a full charge and ended back home with one bar showing and 4 miles on the generally worse-than-useless guess-o-meter. This included under 10 miles of driving between the freeway and home. It was a little surprising that the LEAF charge got so low given that the home-to-home energy use was only about 18 kWh, but the reported 24 kWh capacity of the battery is probably measured at a discharge rate that's lower that what's needed to climb the pass at 70 mph. Also, we know the LEAF hides some reserve charge from the driver.

From this data I conclude that starting from a full charge in Snoqualmie or North Bend, a LEAF can easily make it up and down the mountain at the speed limit without climate control. With climate control on, a bit slower speed may be required.

With a DC Quick Charge to 80% at North Bend, it could probably be done by anyone starting in the greater Seattle metro area.

Having Level 2 charging at the summit would be a big help. Even Level 1 would make a difference for someone spending the day skiing at the pass and wanting to get home with little or no charging on the way back.

Driving at lower speeds would use less charge. Really efficient driving, including better use of regenerative braking on the way down, would further decrease the charge needed.

Comparing the Nissan LEAF and Tesla Roadster

The curb weight of the Roadster is about 2,700 lbs, compared to the LEAF at 3,350 lbs. So the LEAF weighs about 25% more than the Roadster. The LEAF has a more aerodynamic shape, but has a much larger frontal cross-sectional area, so I would expect the LEAF to also have more aerodynamic drag. At freeway speeds, one would expect the aerodynamic drag to be a bigger factor in energy use, but doing a significant climb increases the importance of vehicle weight.

Because of how these two issues interact under different conditions, these numbers tell the story only for this specific drive on this route at this speed. Other drives are likely to give different results, so more tests are needed to get the full picture. It would also be interesting to do the same drive with multiple LEAFs and Roadsters to see how much variation there is between vehicles of the same model.

Data Method and Repeatability

We did everything we could both to minimize the difference between the two side-by-side drives and also standardize the drive so it could be repeated later under either similar or different conditions.

It was warm enough that we had to run the car fans to stay comfortable, but we were able to avoid use of the air conditioning.

We were able to maintain 69 to 70 mph pretty well, with a couple of exceptions. Below are graphs of the Roadster's speed versus time. The LEAF speed profile would be similar, with one exception on the descent, described below.

On the way up, a few minutes after we got onto I-90, we ran into a clump of traffic we had to maneuver through, which slowed us down a little for a few minutes around the 10-minute mark.

On the way down, just a couple of miles from exiting I-90, the Roadster got boxed in between an RV at the same speed in the center lane and a slower vehicle entering just ahead of us. Rather than speed up to jump ahead of the slower vehicle (which would have used a bunch of extra energy), we slowed down sharply to let the vehicle in ahead of us. The LEAF was far enough ahead that it avoided this problem.

Progress on the Roadster Conversion to J1772

2011-06-22T21:57:38Z

We've made some progress on a more robust Roadster J1772 conversion. As part of the conversion, we want a circuit that monitors the J1772 proximity pin and cuts the pilot signal when the latch on the connector is released. With such a circuit, a Roadster will behave as a proper J1772-compatible EV and stop the current flow when the J connector's latch is opened, thus preventing any damage to the connector pins which can occur when pulling out the plug while charging.

Cathy and I worked up the basic idea together and got a bunch of help from the EV community. Cathy put in a ton of work selecting components, soliciting feedback, iterating the design, and designing the circuit board. Our solution works without drawing any power from the car, it just uses a tiny bit of power from the incoming line voltage during charging.

We just got the first set of boards back, put one together, and tested it. It works beautifully, performing even better than I had hoped. The response time from when the switch on the connector is pressed until the pilot signal is cut is about 2.2 milliseconds. When hooked up during a charge, there's no perceptible delay between when the J1772 latch is pressed and when the Roadster stops charging.

Even more geeky information is available on Cathy's page of cool details.

In other news, the cable vendor that said they could produce the replacement inlet assembly cable for us took six weeks of excuses and delays to finally say they don't want to do it. So, we're back to the drawing board on that.

Celebrating Three Years of Driving Electric

2011-06-08T01:56:33Z

Our EV experience started in July, 2008, when we bought one of the few RAV4-EVs that was saved from the crusher. A year later, we took delivery of a Tesla Roadster. For the past three years, we've been committed to drive, test, measure, show, demo, hack, and explain our cars and what they represent to anyone willing to listen.

We have driven the RAV4-EV over 20,000 miles and the Roadster over 18,000. The only maintenance we've had to pay for has been replacing tires and a 12V accessory battery. Since we don't have to take our cars in for oil changes every three months, we have to fill the wiper fluid ourselves.

Sometimes I wonder if the Roadster has lost some acceleration over the past two years, it just doesn't seem that crazy fast to me anymore. Yet when I take someone for a demo ride and they gasp/yell/squeal/swear when I do the 0-60 demo, I realize the car hasn't changed, I've just gotten used to what it can do.

I've broken 100 mph on a quarter-mile drag race track so many times it's boring. I've been in the passenger seat with a real race car driver showing me what the car can do on an autocross track, and then giving me pointers while I drove the same course.

The RAV4-EV is less flashy than the Roadster, but it can haul five adults and a fair amount of cargo. Even with 64,000 miles it's still getting over 100 miles of range per charge, about the same as when it was new. It gets a little less range in the winter, but it still surprises me how little we need to drive beyond its range. Cathy laughs at me when I worry we need to take the Roadster for some lengthy drive, but when I check the distance it turns out to be half of what the RAV4-EV can do on a single charge.

Cathy and I have done enough distance driving in the Roadster that it's old-hat now. With a few strategic Tesla charging stations scattered around, plus maps of places to find alternative charging, planning charging stops is now an opportunity to explore somewhere new that in the old days we would have just driven past. We had a delightful lunch at a scary-looking tavern in Artic, WA, that had the same sort of local regulars you'd expect to see in an episode of Cheers. We have a new favorite burger joint, Burgerville, which means something for two vegetarians. We have made friends in Portland, Ellensburg, Coeur d'Alene, and Vancouver, B.C., and at Puget Sound Energy and the Wild Horse wind farm.

We have talked ourselves hoarse at many car shows (both official and impromptu) and I can't even guess how many people we've had the pleasure of talking to about driving electric. Long ago, I lost count of how many times we've helped a reporter write a more informed article about EVs.

With all we've done and as many people as we've personally reached, it's humbling to know many people in the community who have been doing even more of the same thing, some for decades.

We've made many friends from the Roadster and RAV4-EV owner communities and the broader EV community; too many amazing people to even try to enumerate.

What a wonderful experience it's been to AMP IT UP!

Showing EV State of Charge

2011-06-06T13:56:14Z

Nissan has done a poor job of communicating state of charge to LEAF owners.

The first problem with this display is that you can't tell where you are with a simple glance. Quick: how many bars are there? Imagine if only some are lit up, how long does it take to count them? Once you have counted the bars, you have to divide by 12, or multiply by 8.3%. Like I want to do that while I'm driving! There's a nice number there, 93 miles, but the problem is that number varies wildly based on how you've been driving. Your state of charge might be 40% but the range estimate could be 12 miles if you just reached the top of 4,000-foot pass, or it might be 80 miles if you have been descending from that same pass. Likewise for just getting off of a stretch of 75 mph freeway versus getting onto the freeway after a stretch of 45 mph urban thoroughfare.

Drivers need to know what's in the battery unfiltered by a rating on their recent driving.

This isn't just my opinion, or the opinion of a few old school EV fanatics. I keep hearing from new LEAF owners who after a few weeks of driving realize that the estimated remaining miles on the LEAF dash is not useful. It's not that Nissan did it badly, or that it can be fixed by improving their software, it's not what EV drivers need.

Ford is coming out with the Ford Focus Electric this year and is apparently asking for opinions on what drivers want to see on the dashboard.

First off, Ford should be asking what gas car drivers want to see and putting that in their ads, but they should be asking what experienced EV drivers want to see and put that on the dash. Ford should start with dropping a line to the folks at Plug In America.

When I'm driving, I don't want to see animations or flashy graphics in my main field of view. I'm not watching a movie, I don't need special effects, and I definitely don't need running commentary on my driving. The LAST thing I want to see on the dash is any mention of gasoline. Did the Model T need a gauge showing how many bales of hay had been saved?

Please don't let some gas-driving marketing intern design the dash for an electric vehicle based on talking to other people who haven't owned an electric vehicle.

My wife and I have been driving electric for three years and have logged over 38,000 electric miles. We've done lots of local driving and enough road trips beyond our single charge range that we know what we need.

What I do want to see, in order of importance, is:

Speed, preferably numerical, very easy to read at a glance, the biggest number on the screen.
After speed, the single most important information an EV driver needs is the state of charge, SOC. This should be conveyed as remaining charge energy, in numerical resolution comparable to a mile's worth of driving, and not mangled by some unknown function of my recent driving and road conditions.
Instantaneous energy use. This should be graphical and clearly show whether I'm using or generating energy and how much, even when it's a small amount. Having a number would be nice, but not necessary.
Trip meter, preferably selectable from several. Having a trip meter that automatically resets after each full charge would be cool, but we still want user-controlled trip meters.
Estimated miles remaining based on recent driving is rarely useful, but it would probably be weird to not have it available. Most people think that will be useful until they get used to driving electric. Not having it would be a distracting omission for new owners. It can be on the dash, even on by default, but there should be a way to get rid of it, perhaps making it an alternate to an absolute remaining energy number.

The purpose of showing the state of charge isn't really about figuring out how far you can drive with the current charge. The answer to that question depends on too many factors to ever be a meaningful single number on the dash. Instead, the EV driver needs to answer two simple questions:

1) Do I have enough energy to make it to my destination?
2) If the answer to #1 is "maybe", how do I need to moderate my driving to make it?

Most of the time the answer to #1 is an unconditional "yes". An answer of "no" means it's time to find charging, a condition that should be rare if the car is being used for local driving as intended. If the answer to #1 is "maybe", then I need the best information possible to answer #2.

Note that an estimated range is always wrong when it matters because it assumes my driving style and road conditions are going to remain constant. It's basically telling me how I have been driving. I don't care about that. I need the information that will make it clear how I need to be driving for the rest of my trip.

For this reason, the choice of energy unit for the SOC display is critical. I want something more convenient than kWh, something that will not require doing math to interpret the number. If a vehicle has a certain stated nominal range, which corresponds to X Wh per mile (battery-to-wheel), then the ideal energy unit is X Wh. Tesla calls this an "ideal range mile." Call it whatever you like, but it's a very convenient unit of energy as it tells me how much is in the battery and gives me a range goal I can generally meet or even exceed if I need to.

If a car has a nominal range of 100 miles, then SOC percent corresponds to one mile of nominal driving. That's cool, but it doesn't generalize very well. When next year's model has a range of 140 miles, I don't want to have to multiply SOC percent by 1.4 to get nominal miles.

Showing SOC as kWh is even worse. Not only do I have to multiply by some goofy factor, it's a different factor for every car depending on weight and aerodynamics. Showing kWh used as part of a trip meter is awesome, and showing SOC in kWh has a certain appealing geek factor, but I don't want that to be my best-resolution SOC unit.

We'll all be better off if the car companies start showing SOC as nominal miles now.

On the Roadster, an "ideal range mile" is the amount of energy needed to drive one mile on the combined EPA driving cycle and corresponds to driving level highway at about 57 mph in moderate weather. Knowing this number and my miles to destination tells me how I need to drive to make it. This number slowly ticks down as I drive (occasionally ticking up on a long downhill drive), it doesn't fluctuate wildly as I go up and down shallow slopes and small hills. Nominal miles yields a much more reliable idea of remaining charge than an estimated-miles number can.

Having this number enables useful discussions about range and energy use among owners. If someone is planning a trip over the pass from Bellevue to Ellensburg, I can say that I've done that several times: traveling the ~100 miles over the 3,000-foot pass at 60 mph in moderate weather used 113 ideal miles and closer to the 70 mph speed limit used 119. It also makes planning for elevation possible. Every 1,000 feet of climbing uses up about 7 miles of nominal range, and going downhill gives about half of that back. Knowing that simple approximation makes it possible for a driver to plan a trip over a mountain pass just by knowing the required distance and elevation change. If other automakers use the appropriate nominal mile energy unit, these conversations will work across different makes and models, allowing drivers to share approximate energy expectations without a lot of goofy conversion math.

That probably sounds complicated. Just remember, electric vehicles are intended for local driving within their single-charge range. Most of the time the answer to the "do I have enough charge" is "yes, of course you do." It's only for the rare long trip that figuring things out is needed. Having good state of charge information available all the time will allow new drivers to develop experience and insight from their easy local driving that will make it possible for them to figure out which longer trips are practical. It's critical to widespread electric vehicle adoption that automakers get it right.

EVs at the 2011 Portland International Auto Show

2011-02-05T00:01:00Z

Cathy and I were invited to show our Tesla Roadster in the Eco-Center at the 2011 Portland International Auto Show. Tesla Motors didn't have the resources to participate, so we and Chad Schwitters agreed to show our cars and represent Plug In America in promoting electric vehicles.

Since we got our first EV in 2008, a 2002 Toyota RAV4-EV, we've participated in many car shows. When we started, the EV world was made up of dedicated enthusiasts converting gas cars to electric or holding onto the few vehicles from the early 2000's saved from the crusher (see Who Killed the Electric Car). The Portland show made it clear things have changed: a 30,000 square-foot area at a major auto show dedicated to energy-efficient vehicles, Nissan and GM selling mainstream electric vehicles, other automakers scrambling to jump onto the EV bandwagon, and lots of interest among the show attendees.

The show organizers got in touch with us through our friend John Wayland, who was invited to show White Zombie, the world's fastest accelerating street-legal electric vehicle. John and his team have been advancing the state of the art for 14 years. Not only does White Zombie go from 0 to 60 mph in 1.8 seconds and cover the quarter-mile in 10.2 seconds, it has a driving range of 120 miles. John makes a point of driving it to the track from his home to demonstrate that an electric vehicle can have tremendous performance without making the sacrifices that limit most high-end drag racers to being hauled around on trailers.

We insisted on being placed next to White Zombie so we could hang out with John and his crew, and also point people who thought the Roadster's performance (0 to 60 in 4 seconds) was impressive to a much quicker electric car.

On the other side of us, there was a Nissan Leaf. For people who thought the Roadster's energy efficiency and lack of dependence on oil was cool, but too expensive or impractical, we could point them to a Leaf that costs less than a fourth of the Roadster's price and carries 5 passengers and much more cargo. Nissan had a second Leaf in their main area that was open so people could check out the interior.

They were a day late, but GM did finally get a Volt in the Eco-Center, next to the Leaf. GM also had a Volt in the middle of their main section for the whole show, but it was up on a pedestal and not open for viewing.

To make sure no one thought that EVs were a new invention, there was a 1917 Detroit Electric car on display. These were popular back in the day when cars had to be hand-cranked to start. No one wanted to put up with that inconvenience. It makes me wonder why so many people today are content to put up with the inconvenience of fueling their cars at gas stations and the insanity of sending their fuel dollars into the global oil market that supports really unfriendly governments.

You don't have to drive on four wheels to get the benefits of driving electric: Brammo is marketing a line of all-electric motorcycles.

Straddling the gap between motorcycles and traditional cars are companies like Arcimoto that are building highly efficient, enclosed two-passenger vehicles.

In the fall of 2009, a representative at the Seattle Auto Show told me how the Mini folks were way ahead of everyone else in producing an electric vehicle. The best they have to show so far is a small number of test cars they've put on the market with a one-year lease program. Although it was cool so see the vehicle, it was locked up tight and unattended. The Mini-E could be such an awesome vehicle if they would just get it done and start selling them.

Next year, with even more vehicles available to consumers, I'm hoping EVs will be at the show in force and not relegated to a fringe eco-conscious area. Maybe next year we can be showing front and center in a section dedicated to vehicles that offer instant acceleration, convenient at-home fueling, support for local energy jobs, reduced dependence on the highly volatile global oil market, and increased national security. I suppose we could mention that they are also better for the environment, but I think everyone already knows that.

Understanding Electric Vehicle Charging

2011-01-31T18:39:13Z

Trading a gas pump for a plug is a wonderful thing. It's far more convenient, takes less of your time, and saves you from breathing toxic fumes and smelling like gas for hours after fueling. Charging is a different experience than pumping gas and understanding the subtleties takes time. I've been driving electric for over two years and I'm still learning. Potential EV owners might want to get a head start on the learning curve, and maybe save a bunch of money as a result.

Mostly, I'll relate how charging works for a Nissan Leaf, a four-door, five-passenger hatchback with a range of about 100 miles, but I'll also mention other plug-in vehicles. The Leaf is intended for typical daily driving, which for 78% of drivers in the US means 40 miles or less per day. Occasional longer trips are possible and understanding charging will help you evaluate whether an EV will suit your driving needs.

Level 1 Charging

Level 1 Charging - Standard House Outlet

Level 1 charging is the technical jargon for plugging your car into an ordinary household outlet. For a Leaf, this means about 4.5 miles of range per hour of charging, or about 22 hours for a full charge. Wow, does that sound terrible! But there's a problem with thinking this way: you'll rarely need to do a full charge from flat empty to full. If you drive 40 miles per day and charge overnight, you'll be back to full in 9 hours. When you're sleeping, it doesn't matter if it takes one hour or 9 hours to charge.

But what if you have to drive a lot one day, say 80 miles? Sure, it would take 18 hours to get a full charge, but with a 9-hour overnight charge, you'll be ready for your normal commute the next day. If you drive less than 40 miles per day or charge for more than 9 hours, you'll work back up to a full charge over the next few days.

If you need to drive 80 miles on consecutive days, you'll need an alternative. Maybe you'll drive your other car, that gas-burner you keep around for long trips, or if there's public EV charging in your area, you can charge away from home while you're parked to do your shopping or other errands.

Level 1 charging at work could also be a supplement for people driving over 40 miles per day, or even a substitute for those who can't charge at home (because they don't have a garage or fixed parking place, for example).

Since it's easy to get 40 miles of range charging overnight from 120V, Level 1 is perfectly suited for overnight charging of the Chevy Volt, a plug-in hybrid with a 40-mile all-electric range.

Although Level 1 charging is generally too slow for a road trip, it can be helpful as destination charging. Cathy and I drove 90 miles to San Juan Island, charged for a few days in a friend's garage when not cruising around the island, and left with a full charge. That was great, but I wouldn't want to have to wait for Level 1 charging in the middle of a travel segment.

Beyond range issues, Level 1 may not be suitable for primary charging in all cases. In extreme climates, more power may be required to maintain proper battery temperatures. In these cases, Level 2 charging may be more appropriate (see below).

DC Fast Charging

Blink DC Fast Charge Station
photo by ECOtality

At the other end of the spectrum is DC Fast Charging, the fastest type of charging currently available. It provides up to 40 miles of range for every 10 minutes of charging. These stations are expensive (up to $100,000) and require more power than your house, so you'll never have one of these in your garage.

They are going to start appearing as public charging stations in the next year, beginning in the Leaf target areas. If there's one conveniently located near where you drive, you can get back up to 80% of a full charge while getting lunch or drinking a latte. Charging this fast makes it far more practical to drive beyond an EV's single-charge range in one day. It's still not going to make a one-day 800-mile drive practical, but a 200-mile drive with a couple of charging breaks can be quite doable.

Level 2 Charging

ChargePoint/Coulomb Level 2 Charging Station

Between the cheap Level 1 and expensive DC Fast Charging stations sits Level 2 charging. Level 2 supplies 240V, like what an electric dryer or oven uses. It goes through a box and a cord that improves safety by waiting to send power to the plug until it's plugged into an EV. Level 2 allows for a wide range of charging speeds, all the way up to 19.2 kilowatts (kW), or about 70 miles of range per hour of charging.

However, the charging stations being put in with federal grant money don't support the full range of Level 2 charging and max out at 6.6 kW or around 26 miles of range per hour of charging.

Both Level 1 and Level 2 charging stations simply deliver household electricity to the car. Electronics on board the car transform the wall power into the proper form to charge the battery. This bit of electronics built into the car also has a maximum power rating. The first model-year Leafs can only use 3.3 kW, about 12 miles of range per hour, or about 8 hours for a full charge from empty. The Chevy Volt's on-board charger is also limited to 3.3 kW, although its smaller battery pack gets full sooner.

Nissan recommends that you install a Level 2 charging station at home. That's a reasonable thing to do if you don't mind spending about $2,000, just consider it part of the cost of the car. Early buyers in the Leaf target markets may be able to get into The EV Project and get a free Level 2 charging station plus an allowance toward the install cost. Failing that, there's a 30% federal tax credit (up to $1,000) for installing EV charging, which can make it less expensive. Still, if you are planning to use your EV for a daily commute of 40 miles or less per day, you should at least consider using Level 1 charging at home. You can always add a Level 2 charging station later if you decide you need it.

There will soon be 20,000 public Level 2 charging stations (limited to 6.6 kW) installed mainly in the Leaf target areas. Even if you only have Level 1 charging in your garage, if you're in the early rollout areas, you should have access to convenient Level 2 charging available while your car is parked and you're doing something else. These charging stations will make it possible to drive 60 miles to a baseball game and pick up about 50 miles of range in 4 hours while you're having fun, thus easily driving over the single-charge range while always keeping a healthy reserve.

Charge Time and Battery Capacity

It's misleading that charging times are generally quoted as time for a full charge. While it does take about 22 hours (Level 1) or 8 hours (Level 2) to charge a Leaf from empty to full, you're not likely to do that often because you will rarely arrive home with a fully depleted battery. It doesn't matter if you're driving a 40-mile Volt, a 100-mile Leaf or a 240-mile Tesla Roadster, if your commute is 40 miles, you'll only need about 9 hours (Level 1) or 3 hours (3.3 kW Level 2) to charge.

When we bought our Tesla Roadster, we got the high-power 16.8 kW Level 2 charging station, which can charge the car in 3.5 hours. After driving the car for a few months, I realized it's all but pointless to have such a big charging station in our garage. It's rare that I drive over 40 miles in a day. The 16.8 kW charging station can restore 40 miles in under 40 minutes. I want that charging speed when I'm making a long trip, not when I'm sleeping at home. In fact, I manually drop the power I pull from the charging station to about 7.5 kW because it's a little nicer to our electrical panel and the grid, and my typical overnight charge is still under 2 hours. Ignoring the fact that Tesla is still using the now-incompatible proprietary charging plug they picked before there was a chosen standard, most people buying a Tesla Roadster today would be well-served to buy a 6.6 kW charging station for home.

3 Roadsters Sharing the Charging Station at Burgerville

Level 2 Charging, Road Trips, and Charging Speed

Already, Ford has announced that the upcoming electric Ford Focus will support charging at 6.6 kW, and is making fun of the Leaf's 3.3 kW Level 2 charging limit. By the time Ford actually starts delivering the electric Focus, Nissan may have already upgraded the Leaf to 6.6 kW charging. I don't think it will be long before mainstream EVs are capable of even faster charging. The Tesla Roadster can charge at 16.8 kW, which combined with a larger battery pack makes 400-mile drives possible even without DC Fast Charging. Given that Level 2 charging costs 1/10 of what a DC Fast Charger does, I can imagine a lot of driving being supported by full Level 2 charging stations in areas that can't justify the investment in DC Fast Charging.

Personally, I'm disappointed we're spending so much money installing these 6.6 kW public charging stations rather than full-speed Level 2 chargers when most of the expense is usually just running the wires and buying the fancy box. A typical commercial Level 2 install runs around $10,000 for a charging station that's connected to a network and capable of billing the user. Cranking those charging stations up to the 19.2 kW limit would add a small incremental cost, perhaps 10%, and would allow for much faster charging. If you're a business owner installing a charging station and have to dig a trench and/or run conduit, even if it's just a for 6.6 kW unit, I strongly recommend planning for running 100A wire later without having to retrench or replace conduit so that upgrading to a 19.2 kW charging station will be much less expensive.

2008 Tesla Roadster Converted to J1772 Charging

2011-01-06T01:30:00Z

Cathy and I, with help from Dave Denhart and many others in the Tesla and broader EV communities, have converted our 2008 Roadster and Tesla High Power Wall Connector to use the new industry standard J1772 inlet and plug. This will allow us to charge without an adapter at the tens of thousands of Level 2 charging stations that will be installed in the US by the end of 2011.

What we have is functional and completely reversible, but not ideal; we view this as a version 0.9 conversion. As there are very few J1772 charging stations currently installed, and the numbers probably won't take off until late spring or early summer, we have time to develop a better solution before it actually becomes compelling for Tesla owners to convert in significant numbers. I'm sure Tesla Motors could do a much better job of creating an integrated solution and I would prefer that to having the owner community develop a conversion solution.

We've hear rumors that Tesla is developing an adapter, but are still waiting for official word on what, if any, J1772 solution they will provide. While an adapter would give us a way to charge, we have heard from many owners who would prefer to convert their vehicles and charging equipment to the industry standard rather than leave an expensive adapter vulnerable to theft while charging.

Our effort started last summer when Cathy and I began working with Dave to figure out what it would take to build an adapter that would let a Tesla Roadster charge from the Level 2 J1772 charging stations. We discovered that SAE adopted Tesla's extension to the older J1772 communications standard, so a simple pass-through connector that converts Tesla's charge inlet to the J1772 inlet will allow charging to occur, although there is an issue, which is explained below.

Once we understood the protocol, Cathy and I built and tested a pass-through adapter. When I let the Tesla owner community know about our adapter in mid-September, I wasn't surprised to hear that lots of owners were thinking about those thousands of chargers, but I was surprised how nearly all who expressed an opinion agreed with us that the right way to do this was just to convert the Roadster to use the J1772 inlet. From what I'm hearing from new and prospective owners, it seems to me that many potential Roadster customers are put off by the Tesla plug and this is probably already becoming a barrier to sales.

In the absence of any word from Tesla Motors about a J1772 upgrade path, we've been slowly working toward doing a conversion ourselves. A few weeks ago, we finally obtained an ITT Canon 75A UL-approved inlet and plug pair from Clipper Creek. The plug cord is intended as a replacement cable for Clipper Creek's model CS-100, and carries the same power and signal wires as the TS-70 aka Tesla's High Power Wall Connector (HPWC, formerly the HPC). Clipper Creek also sells a holster for the J1772 plug that can be used to replace the holster for the Tesla plug.

With the necessary hardware in hand, we starting tackling the engineering challenges in getting the inlet mounted inside the Roadster's charge port: there's limited space to work with and the Roadster wasn't designed with the shape of the J1772 plug in mind, so getting the plug and cord to clear the body is tricky. It took a bunch of measuring, brainstorming, numerous experiments, a couple of laser-cut bracket prototypes, some Dremel work on the inlet cup, and then an adapter designed in CAD and printed on a 3D printer to get something functional.

This is what the back of the upgraded inlet port looks like. The blue piece is the mounting plate Cathy designed in CAD and we fabricated on a RepRap 3D printer at Metrix Create:Space.

Here's the work in progress just before installing the J1772 inlet and putting it all back together:

Here's the inlet mounted in the Roadster's charge port:

The ITT Canon cord plugged into the Roadster's charge port:

Charging from our HPWC, now converted to J1772.

The top of the inlet tilts back to angle the J1772 cord up. This works pretty well for the ITT Canon cord with enough clearance at the top of the port that it's easy to slide the plug in and engage the lock, easier than plugging in the Tesla connector in fact. The rubber strain relief on the cord barely rests on the body, plus our Roadster has the paint guard protection there, so I'm not worried about that minor contact damaging the paint.

It's not quite as nice with the plug and cord used by the ChargePoint Coulomb chargers, but I think it's OK for use on the occasional road trip.

In addition to the cable clearance issue, there's another concern with our v0.9 conversion strategy that has to do with the largest difference between the Tesla and J1772 communication protocols.

The Tesla plug uses four contacts: two for power, one for ground and one for the pilot signal. The pilot signal is a low-voltage communications protocol that allows the charging equipment to tell the car the maximum amperage supported and allows the car to ask for the power to be turned on and off. The pilot signal is not connected to the car until the plug is connected and the locking switch is engaged. This switch plays a second role: if the driver tries to remove the plug in the middle of a charge, sliding the switch back interrupts the pilot signal which tells the car to stop charging. This happens very quickly so that the driver cannot get the plug untwisted and removed to break the electrical contacts while current is still flowing. It's important to prevent this because doing so can cause arcing, which would damage the contacts.

Instead of interrupting the pilot signal, J1772 uses a fifth wire for this purpose. Like the Tesla plug, the locking mechanism on the J1772 plug makes the proximity connection, so that when the driver wants to remove the plug and slides the lock it interrupts the proximity connection, thus telling a J1772 car to stop charging immediately (within a tenth of a second). Unfortunately, the locking switch on the J1772 plug doesn't interrupt the pilot signal.

With our v0.9 conversion (or a simple pass-through adapter), the driver can unlock the J1772 plug without the car knowing, and then pull the plug while power is flowing. Cathy and I need to make sure we don't do that. To solve this issue, we need to design a circuit that watches the proximity pin and interrupts the pilot signal when the J1772 plug is unlocked. I don't expect this to be difficult, but we haven't done it yet.

We have already made some improvements in the design. This is version 3 of Cathy's inlet mounting plate design, which we plan to print for our next revision:

In addition to the improved mounting plate, our next steps are:

1) Hope that Tesla Motors provides an official conversion solution before it matters to most owners, thus saving us the remaining steps.

2) Design a circuit to monitor the proximity pin and disconnect the pilot signal when the J1772 plug is unlocked.

3) Test with other J1772 plugs and possibly work on a better solution for cable clearance over the body panel.

4) The 2010 and later Roadsters have the inlet cable assembly connecting to the PEM in a different location. There may also be other differences. We haven't looked into it yet and don't know if it will be more or less difficult to convert than the 2008 Roadsters.

5) Before recommending an unofficial conversion to other owners, we'll need to find out how this will impact our warranty. Tesla Motors has been cooperative with our efforts: they sold our group an inlet cable assembly so that we could do the conversion reversibly. We hope they will continue to be supportive rather than forcing us to wait until our warranties expire before being able to effortlessly access standard J1772 public charging stations.

An End to the Dark Ages of EV Charging

2010-10-10T03:55:50Z

I had the opportunity to test out another ChargePoint charging station today. I was more prepared than I was the first time, so I got to try out the whole experience. I'm so pleased to see the future of electric vehicle charging. I'm not going to miss charging at RV parks at all.

This time, I had my access card activated and attached to my ChargePoint account. The easiest way to do this is to go to www.mychargepoint.net, sign up for an account and order a card. It's best to do this well in advance of wanting to charge. (Other charging station companies may offer similar functionality, but so far I've only been able to try out ChargePoint chargers installed by Charge Northwest and EV Support.)

I also downloaded the ChargePoint App to my iPhone and logged into my account.

Step one in the charging process is to locate a charging station. This can be done with the iPhone app or through the ChargePoint Find Stations web page. Not only can you find stations, you can check to see if they are functioning and available.

When I arrived at the charging station, I removed the J1772 cord from the station by sliding the silver button back to release the catch.

Next I plugged the cord into the car. My car requires a plug adapter, which doesn't yet exist, so Cathy and I hacked one together. Modern EVs will just have the right receptacle on the car, so you won't have to fool around with the ludicrous cable adapter shown here.

(photo courtesy of Michelle Billmaier)

To start the charging session, the user either places the ChargePoint card against the labeled spot on the charger (as shown above), or taps the pin for that station on the iPhone and then taps the start button. Theoretically, you don't even need to carry the ChargePoint access card, but it seems like a good idea just in case you can't get cell reception.

After starting the session, refreshing the screen will show the pin has changed colors from green to blue so that other EV drivers can tell that it's in use. Tapping on the pin will show that the start button has changed to a stop button. (Tapping the yellow button will show driving directions to the charging station.)

Checking the car's info screen shows that the charge is underway.

In the old days, when we took an electric vehicle on a road trip, we had to charge from outlets at RV parks and were confronted with an unpleasant problem...

Once you get the charge started, it's pretty boring: the car charges while you watch. You'd like to leave the car and go do something more interesting than watch it charge, but if you do that you risk having the charge stop early (like 5 minutes after you walk away) because of some problem. Maybe the breaker popped, or something interrupted the power briefly, any number of things. When you come back, perhaps hours later, you're not happy to find the car is still in the same state of charge as when you left, so now you have to do it again, and this time you're going to babysit it the whole time.

This is where using networked chargers designed for this purpose really shines.

If you're charging from a ChargePoint charger, you can check your charge session's status either from the iPhone app, or through a web browser (perhaps at a cafe, or in your "kabin" room).

Wait though, it gets even better.

Suppose the more interesting thing you want to do is sleep, because you've been driving all day. It's not very convenient to check the session status every few minutes while you're trying to sleep. Even if you're eating dinner or surfing the web, you don't really want to constantly check your charge session. (See how quickly we get spoiled? Previously, there was no way to check the charging without being at the car, and yet now we don't want to have to bother with refreshing the screen on our iPhone.)

You can configure your ChargePoint account so that you get a text message or email for any or all of four events: charge completed, charger unplugged, ground fault error, or over current error.

To test this, I unplugged the cable from the car while it was charging. Shortly after that, I got a text message:

The only thing cooler than getting that message is knowing that not getting that message means your charge is still running.

And so we see the start of a new era and the end of the dark ages of EV charging.

J1772 Charging for the Tesla Roadster

2010-09-14T22:00:00Z

We are about to see a mass deployment of public level 2 SAE J1772 charging stations, over 14,000 from The EV Project alone. This compares to fewer than 100 public Tesla charging stations (240V/70A High Power Connectors, aka HPCs). Over the next 12 months, I expect that the availability of level 2 J1772 chargers will totally overwhelm all other charger types.

While most of these 240V chargers will be limited to 30A or 32A, J1772 chargers capable of supplying 240V/70A are available from Clipper Creek with many other vendors also working on charging stations.

Teaming up with a number of other Tesla owners and members of the broader EV community, Cathy and I have been looking into what would be required to bring J1772 charging support to the Roadster community.

The good news is that Tesla and J1772 use the same communications protocol to establish the connection and start/stop charging. This didn't happen by accident. Tesla Motors was involved early on in the development of the J1772 spec. But the Roadster was designed before the new J1772 committee even got going, so the Tesla charging protocol was designed based on the old J1772 specification which used the Avcon connectors and limited charging to 40 amps. Tesla extended this protocol up to 70 amps, and successfully lobbied the J1772 committee to adopt this extension. Cathy and I have confirmed that the SAE J1772 JAN2010 spec exactly matches the amp limit waveforms produced by the Tesla HPC at all amperage limits from 12A to 70A.

So, the Tesla Roadster uses the same communications protocol as J1772. (Except for the button on the HPC that can be used to start charging; I don't know how that works.) The only barrier to charging a Roadster from a J1772 station is the Tesla plug. We confirmed this by building a proof-of-concept adapter and using it to charge our Roadster at a Level 2 J1772 charging station in Olympia, WA, last Friday (Sept. 10, 2010).

We'd like to thank Dave Denhart, Rich Kaethler, Chad Schwitters, Martin Eberhard, and Dave Kois for helping us with this proof-of-concept project. Thanks also to Jim Blaisdell of Charge Northwest for helping us find a level 2 charging station and getting us a ChargePoint Network card overnight. Our crude adapter is not a robust solution. As you can see it's quite bulky (since we didn't want to cut the cable to a working Tesla plug) and isn't watertight enough for general outdoor use.

When the Roadster was entering production, there was no standard J1772 plug, so Tesla had to design their own. That was a necessary step, but now that the final standard uses a different plug, I think we need to find a real solution to this incompatibility. As I see it, there are at least 4 possible solutions:

An upgrade to switch both the Roadster and HPC to use J1772 connectors.
A compact adapter that converts J1772 to the Tesla connector.
A new pigtail for Tesla's universal mobile connector (UMC).
A new pigtail that requires purchasing a re-engineered UMC.

A new pig tail for the current UMC (solution 3) isn't very appealing as the UMC is limited to 40A, cutting us off from any 70A J1772 chargers, while also requiring us to stuff a large, heavy, awkward cable into our trunks just to charge at a station that is guaranteed to have a cable that will reach our charge port. It's also not nice for those of us who have already invested in a different mobile connector, like the original MC240 or the RFMC. Solution 4 is even worse than 3 as it shares all of the problems and it would require everyone to purchase a new mobile connector.

A compact adapter (solution 2) is better in that it could support the full 70A charging and also be quite compact, little more than a J1772 receptacle and a Tesla plug. It will still be quite expensive as it requires a Tesla plug. My guess is that it would cost at least $1,200 retail, based on what Tesla charges for the MC240 and UMC. It also has the downside of being an obvious target for malicious theft when the car is left charging unattended. Nissan Leaf owners won't have to leave an expensive, unsecured device dangling from their cars when charging, why should we?

Full conversion to J1772 (solution 1) sounds radical until you see a J1772 receptacle. It's very close to the size and shape of the inlet in the Tesla charge port. Once I saw that, it required zero imagination to picture a Tesla Roadster with a J1772 receptacle in place of the proprietary Tesla charge inlet.

The downside of solution 1 is that it would also require replacing the plug on our home chargers (HPC or mobile connector). This could be done by either replacing the cable, or by using the old Tesla inlet and a J1772 cable to make a Tesla-to-J1772 converter.

The retail cost of an ITT Canon UL-certified J1772 receptacle and cable pair rated for 75A is $825 from Current EV Tech. I don't know of anyone else selling these newly-available connectors, but I do expect it to be a competitive market much larger than just Roadster owners. Even adding in reasonable labor costs, it seems to me that converting a Roadster and HPC should be near or below the cost of a J1772-to-Tesla adapter.

I have been told that Tesla Motors is investigating ways to bring J1772 support to the Roadster which may include either a compact stand alone adapter (option 2) or a J1772 pig tail for the Tesla universal mobile connector (I'm not sure if this is option 3 or 4). They are early in the process and not promising anything at this point. From what I have heard, Tesla Motors is not interested in providing a full J1772 conversion (option 1) and hasn't even committed to supporting J1772 on the Model S.

It's possible the full J1772 conversion could be done even if Tesla Motors doesn't give us an official way to do it. I expect our group will continue exploring ideas in case we have to tackle the problem ourselves.

We are several months away from having a significant number of Level 2 J1772 chargers installed in metro areas targeted by The EV Project, and even further away in other areas of the US. There's plenty of time left for both Tesla Motors and the owner community to explore possible solutions, but I believe this will soon be an important issue for every Roadster owner who wants to be able to take advantage of the soon-to-be pervasive J1772 charging infrastructure to conveniently drive beyond the Roadster's single charge range.

Tesla Roadster Charging Rates and Efficiency

2010-07-20T16:32:27Z

Note that the graph cuts off the last three hours of the 16A charge. The 120V charging graphs aren't shown. A full standard mode charge at 120V/16A takes about 38 hours and at 12A it takes about 60 hours.Note that the graph cuts off the last three hours of the 16A charge. The 120V charging graphs aren't shown. A full standard mode charge at 120V/16A takes about 38 hours and at 12A it takes about 60 hours.Updated: April 17, 2011 to add 120V charging data.

The Tesla Roadster offers a wide variety of charging options, from 120V/12A up to 240V/70A. Charging at higher voltage and current charges faster, but most of the time charging speed isn't an issue. If you drive a typical commute and charge at night, even the lowest power will get the car fully charged overnight. At least with the early Roadster firmware, charging at 120V was pretty inefficient because of the fixed charger overhead, but what about charging at 240V at various amperage limts? My theory was that charging at higher current is more efficient because you spend less time paying the charging overhead, but another owner challenged that assumption with the theory that higher current is less efficient because it generates more heat and thus increases the amount of energy spent keeping the battery pack cool.

Another aspect of charging is that for any given current setting, the Roadster will charge steadily at that current until it gets near the top of the charge, at which point it will start to taper off. This reduces your charge rate near the top of the pack. This aspect of charging isn't documented in the owners manual.

If I don't care about charging time, what's the best amperage for energy efficient charging? If I'm on a road trip and want to squeeze the most range out of time spent at a charging stop, how should I space my stops and how long should I charge at each one? I've collected enough data to shed some light on these questions.

Methodology

I performed a series of charges at various current levels from relatively low battery states up to a full standard mode charge. For each charge, I collected time, voltage and amperage once per minute, and state of charge once every 10 minutes. From that, I can compute energy used during every segment of the charge and the total energy used.

To track our energy use for driving, we have a dedicated electric meter for each of our EVs. To validate my energy calculations, I verified that the total energy calculated per charge matches the value computed from the meter readings.

All charging was done overnight in cool weather with a 2008 Roadster. The 16A charge was done with firmware version "3.5.17 15", all other runs were done with firmware version "3.4.17 15". The 16A charge stopped at a lower state of charge (96%, 188 IM) than I normally see (98%, 193 IM). I don't know if this is due to the lower current limit, the new firmware, or a one-time fluke.

Charging Efficiency Results

Is it more efficient to charge at a low rate or a high rate? Here are the results:

Charge Rate	Wh per Std %	Wh per Ideal Mile
120V - 12A	807	414
120V - 16A	723	371
240V - 16A	589	306
240V - 24A	544	282
240V - 32A	527	274
240V - 40A	512	266
240V - 48A	524	272
240V - 70A	516	268

As you can see from the table, there's not much variation in charging efficiency when charging at or above 240V at 32A, but energy use rises noticeably at lower power levels.

Road-tripping and Charging Rates

Also of interest are the charging rates at various current levels. This is especially important when charging away from home.

Charging at higher currents is faster than lower current, but by how much? Is it worth it to drive 55 mph in order to make it to a 40A charge point instead of driving faster and stopping sooner at a 24A or 32A charging spot? Tesla gives us a table on charging rates, but it's pretty low resolution.

How far can I charge before I start getting diminishing returns because of the current tapering that happens near the top of the charge? Tesla is silent on this subject.

If you care about getting the most out of your charging stops, you may be in Range Mode, so this table shows both standard and range mode values for when current begins to taper off.

Charge Rate	Ideal Miles per Hour	Current Tapering Begins At:
Charge Rate	Ideal Miles per Hour	Std %	Std IM	Range %	Range IM
120V - 12A	3.3
120V - 16A	5.1
240V - 16A	13	93	179	82	205
240V - 24A	20	94	180	82	205
240V - 32A	28	93	178	82	207
240V - 40A	36	93	178	81	204
240V - 48A	42	91	174	80	201
240V - 70A	61	84	161	75	188

Let's assume I want to get the most range for time spent charging, and don't need to charge all the way to the top. From the above table we see that if I'm charging at 48A or lower, I can expect to see the charging rate start to taper off at around 80% or a bit over 200 ideal miles (range mode). If I'm lucky enough to be charging at 70A on the road, my charge rate will start dropping around 75% or 188 ideal miles. I'll keep charging above 40A until I hit that 80%/200IM mark, so if my next charging stop is only 40A, I may as well keep charging to that point.

I'm sure there's some variation from car to car, and the pack and ambient temperatures will change charging behavior, so don't plan your trip to depend on these exact values, but this is at least a rough guide.

Charging Profile Graphs

Let's start by looking at how the state of charge varies over time using different current limits at 240V. All charges are standard mode all the way up and normalized so that all the charge sessions are shown from the same starting point, around 36%.

You can see how more current yields a faster charge, and that the rate of charge starts to drop off as the battery pack gets near the 100% mark.

Now let's examine current draw and state of charge throughout each of the current settings. In each session, the car draws an approximately constant amount of current until near the top of the charge when it begins to taper off. The following graphs show current drawn (in amps) and state of charge (as standard mode percent) as a function of charge time in hours. Each charge begins at a slightly different level, but all start below 40% so they have a nice long stretch of steady current draw.

You may notice that at 32A and 40A, the rate at which the SOC increases doesn't drop off as much as you might expect from how quickly the current drops near the end. I attribute this to the SOC calculation stabilizing near the end of the charge. It's difficult to know how much charge is in a battery while you're charging it. My guess is that the SOC is an estimate that gets better near the end of the charge. Regardless, the less current you're drawing, the less power you're putting into the battery. I've seen behavior that leads me to believe that if you stopped the charge within the tapering zone, you'll see the SOC continue to rise for a bit as the software gets a better estimate of the charge in the pack. However, you're still getting diminishing returns on charge time once the current starts to taper.

Another way to look at the data is to plot amperage draw as a function of state of charge. This will show us how the different charge limits compare with respect to when they start backing off from the full allowed current.

From this, we can see that there's isn't a penalty for charging at higher amps. Although it starts tapering the current earlier, it hits the lower amperage levels at about the same point as charging at those amperage values would start tapering.

Charging in Range Mode

Each of the above graphs show a standard mode charge. In range mode, it makes the bottom part of the charge range available and charges the pack even further: 0% and 100% in standard mode correspond to 11% and 87% in range mode. The same charging profile is in play, so as the battery pack crosses beyond the top of the standard mode charge, the current draw drops even further.

Tesla says that the range of the Roadster is 244 miles and that it can be charged from empty to full in as little as 3.5 hours, but those two don't really go together. The 3.5 hour charge time is for a full standard mode charge which is less than 80% of the full range, around 195 miles. Getting the full range mode charge takes longer. For my car, it's about an hour and forty minutes to go from a full standard mode charge to a full range mode charge (and add more time if you start below 10% in range mode). So, if you're on the road trying to make good time, waiting the extra 1:40 for another 25 ideal miles is not worth it unless you need the full range to get to the next charging stop. Charging to the top of range mode only makes sense if you're charging overnight and don't care how long it takes. So, on an extended road trip, a full range mode charge is probably only useful at most once per day.

Topics for Further Research

I would like to add data for some more scenarios, most notably 120V/12A (the slowest of the options, which requires three days for a full standard mode charge).

It will be interesting to see how these graphs change over time as the battery pack ages.

Charging in a hot environment definitely changes energy consumption during charging because the fan and A/C will kick on to cool the battery pack. It's harder to control for ambient temperature across multiple charges, but it would be interesting to collect data and see how things change. I would not be surprised to see a significant penalty for charging at higher current if that pushes the temperatures high enough to require the A/C during the charge.

These results are for our Roadster, yours may be different. Even the conversion from standard mode percent and ideal miles to range mode may vary between vehicles and across firmware updates. Drop me a note if you want to learn how to do this analysis for your Roadster.

Collecting and processing the data to produce the charts is only partially automated. It would be nice to automate more of the process to make it easier to do the analysis for me and others who are interested in doing the same for their vehicles.