Electric Bug: Driving and watt-hours per mile
I now have over 3000 miles on my car. Up till today, the only problems I have had have been with the IOTA DC-DC Converter. I’m supposed to have a replacement soon, as my IOTA may fail again at any moment.
Now that I have some driving experience, I have a better idea of the range. It’s not good to say that an electric car gets X mile range, since X various by many factors. Those factors are: how heavy you are with the pedal to accelerate, how hard and often you brake, how many hills you drive up and how fast you drive. I have one big hill on my commute (or, when I go *anywhere*), so I can never remove that factor, and I always want to drive at least the speed limit. But I can control how “soft” I drive.
If I drive the car “soft”, meaning reasonable acceleration and driving at the speed limits on the freeway (usually 65 mph), I could get a 100 mile range to 0% State of Charge (SOC). Last Sunday I drove 64 miles according to my odometer (or, about 62 miles according to google maps). The BMS said it took 122.3 Amp-hours and the SOC was at 39%. This drive was mostly at 65mph, aside from the 2 miles driving up my “driveway”, and then going 50-55 up and down highway 17. I had maybe one stop light each way on my trip. 122.3Ah * 48 (number of cells) * 3.2V (nominal voltage per cell) = 18785 Watt-hours (18.8kW). 18785.28Wh / 64 miles = 294 Watt-hours per mile. The batteries are rated at 200Ah. So: 200Ah*48*3.2 = 30720 Watt-hours of energy in the battery. 30720Wh / 294Wh/mile = 104.5 miles.
So, a good “soft driving” estimate for my bug, including a large hill and mostly 65 MPH on the freeway, is 104 miles. Generally, I don’t want to do this, as taking the battery lower than 20% is not good for cycle life. I also don’t have my BMS setup to limit power when voltage drops to a certain level, so it is dangerous (meaning, I could cause damage to expensive cells).
If you are doing a bug conversion, use about 300 Wh/mile as an estimate for what you can get. I rarely get better Wh/mile, but that is because of my huge hill I drive up. Wh/mile would be better if I didn’t live in the Santa Cruz mountains.
Now, if I drive “harder” I can get about 375 Wh/mile. That’s about an 82 mile range. So, I can probably safely say my range is from 70 to 100 miles per charge, but I probably won’t want to go more than 80 miles to keep it “on the safe side”.
I love your articles. Leave it to a programmer if you want the real nitty gritty on actuals and a very complete explanation. I’m in Florida. It’s very flat here and I drive about 30 miles a day rarely exceeding 50mph. I think your bug would be incredible here. You would however need A/C which would be a drain. I am a long time VW guy and will sometime soon do a conversion.