DRIVING TIPS FOR THE
GM EV1 ELECTRIC CAR
- The following is written by Peter Ohler who has been driving electric vehicles for many years. -
I am a happy lessee of an
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). It looks good and has all the amenities; CD player, air conditioning, and much more.
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:
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 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 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.
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.
Getting the most range out of your EV1 takes some practice. Here are a few tips that may help squeeze the last few miles from the car when you really need to. If you don't need to have fun and drive it any way you like.
1.Keep the amps low This seems like an obvious one one characteristic of lead acid batteries is that the more amps you pull from a battery the fewer amp hours you get out of it. That mean stomping on the pedal detracts from the range even if you coast after that. Try to hold the average amp draw by avoid surges in power even if they are small. Accelerate very slowly. On hills try to keep the same power going up as going down (within reason of course). Remember you want to avoid surges in power if at all possible, which leads to the next hint...
2.Plan ahead The goal while driving is to use every bit of the battery capacity to move you down the road. You never want to throw any of that momentum away by using the brakes or even the regen coast down. So plan for those exits and turns and let the speed drop due to drag and friction. Don't follow too close behind other drivers or else you will end up using the brakes. Try to time the stop light so you can just keep on rolling. Lost momentum has to be made up so lose a little speed earlier so that it takes longer to get to the light. If at all possible make the trip when there are fewer cars on the road so you can drive like an EV extending its range without getting other drivers angry.
3.Drive Slower This is a tough one to follow but it makes a big difference at highway speeds. The EV1 has a low drag coefficient but speed still makes a significant difference. If you have a way of measuring amps drawn try it and see. Power required at 70 is quite a bit more than at 50 or even 60.
4.Keep the windows up When driving on the highway keep the windows up. Use the vents to stay cool. If that's not enough then use the AC. The AC draws less than the loss from putting the windows down.
5.Use the coast down When possible use the coast down feature instead of the brakes. It would be best not to use either but sometimes you have to stop or slow down. The coast down puts more back into the batteries than the brakes since no friction braking takes place when using the coast down. I usually drive without the coast down button pushed in and then push it in when I want to slow down.
6.Experiment Try different techniques and see how they work. You will need something to give you feedback for small differences in driving patterns. My EV1 Dash program and hardware hookup will do the trick or else you can write your own data collection software. On the numeric display keep an eye on the net amp hours used and compare that to the drain. The closer those number are the better you are driving. If you keep a constant 25 Amps the number should match exactly. Pull lots of power and they diverge. The more power used the more they diverge. Strive for a different of less than 15%. A careful driver pushing for range can get under a 10% difference. Regen should also be as low as possible.
Written by: Peter Ohler
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