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I really liked the EV1. It's a great car. A real step up from the previous electric vehicles; an electric pickup in the late 1980s and more recently a converted Toyota Paseo. Here's a thumbnail picture of both the EV1 and the Paseo charging together in my driveway. Click on the small picture to get a bigger version.

The EV1 is faster (0 to 60 in 7.6 seconds according to Popular Mechanics) and has a longer range (50 to 90 miles per charge for the original lead acid version). It looks good and has all the amenities; CD player, air conditioning, and much more.

At one point we had 2 EV1s. That was before the recall. After that we reverted back to a single EV1, one iof the 1999 models with NiMH batteries. The range was much farther but the acceleration was not as good as the 1997 lead acid version. The newer gen II model handles better though. Almost like a sports car.

Range and what's with these gauges?

One of the biggest problem right now with EVs is the limited range. Batteries are just not good enough yet. As a result its very important to have enough feedback from the car to be able to change your driving habits to get the most out of the battery pack. To do this you need a good "fuel" gauge and some idea of how much fuel you are using. The fuel in this case is the amount of the battery capacity available. The EV1 has a pretty good state of charge (SOC) gauge that gives a fairly accurate reading of how many amp hours are left in the pack. Unfortunately its very coarse with only 11 bars to indicate the SOC. The indicator for power use uses the same set of bars and is set up as almost a log scale of the power being used. There is also a range estimate that makes a guess at the remaining range based on past history.

After driving the car once or twice it was pretty obvious some improvement or enhancements could be made to the range and SOC gauges. It was rather surprising to see the range increase as I drove instead of decreasing and when the pack got low the miles slipped away a lot faster than when the pack was full. I've also noticed that the SOC seems to be based strictly on the amp hour capacity of the battery. Unfortunately lead acid batteries have this annoying problem of sagging as loads are applied. This means the voltage drops the more amps are pulled from the pack. This effect is even greater when the SOC is low. To hold the same power level more amps must be drawn from the pack when its at a low SOC than when its at a high SOC. This effect can become very significant. At 100 amps there is about a 10% difference, at 200 amps its up to 14%, and at 300 amps it's nearly 20%. So the deficiencies with the current gauges are:

  • Range gauge is based on too much history
  • SOC gauge is not power compensated (and not linear with actual SOC)

Better gauges

Before explaining the solution to the gauge deficiencies let me provide some background. On the electric Paseo I had an E-Meter that had a serial port on the back of it. I wrote some software for the PalmPilot (Palm Computing Platform) and collected voltage and amperage reading once a second from the car. After much analysis and experimenting the PalmPilot software was good enough to use as the SOC gauge for the car. From this experience I learned a lot about lead acid batteries, particularly gell cells (Optima yellow tops) like the ones in the EV1.

Now that I have an EV1 to drive I couldn't pass up the chance to collect data from it. It turns out there is a diagnostics port under the dash on the drivers side that produces a steady stream of data. Unfortunately there are no documents on the port. Even the service manuals don't cover it. After some help from others and lots of feedback experiments the codes are at least partially broken. The PalmPilot software has been updated and is collecting data from the EV1. It now provides alternative views or gauges of the battery pack status with a more fine grain and more accurate SOC gauge and several range indicators based on several power use cases. The PalmPilot software I wrote is available for download and more information is also available. I've also put together some notes on how to hook up to the port and how to parse the data stream. The data collected can be graphed using a simple Java program which can be downloaded as well.

Driving tips

After driving EVs for a few years and watching the gauges you learn how to drive to get the most range from the batteries. The EV1 is like any other EV in many ways but there are some interesting differences. I've assembled a number of driving tips based on my experience so far.

Links to other EV related sites