Plug Bug: analyzing data

Electric Bug

I finally have the car running again! I got the controller back from Netgain Controls with an upgraded motherboard to fix some issues I was seeing. My Interface Module was also fixed to report the accurate voltage.

Here’s some data from the drive home as logged by the controller.

Total amp-hours consumed: 41.955 ah

Watt-hours, based on my 48 cell pack at 3.2v nominal, for 153.4v: 6444 watt-hours

Watts per mile, based on the 20-mile drive home, including highway 17 at 50-55 mph: 322.2 watts/mile.

That is what the controller is consuming; the battery has some extra draw to maintain the 12v battery via the DC-DC converter.

Let’s consider 322 watt-hours/mile as the average, although that was fairly conservative driving (not punching the throttle at lights, and coasting to a stop when I could).

The pack has: 48cells*3.2v*200ah = 30720 watts (30.7 kilowatts) of energy. At 322 watts/mile that would give a range of 95 miles. Give that I shouldn’t take the batteries lower than 20% depth of discharge (DOD) to get a high cycle life (and ensure I don’t kill cells), that give me a safe usable range of: 76 miles. Say 75 to be safe.

So, my range with my driving conditions is 75 miles. I could eek out 10 more if I really had to.

Here’s a graph of the voltage as I drove home. About 2/3rds the way through you can see it dropped quite a bit; that was driving up Highway 17:

Screen shot 2011-03-08 at 7.53.10 PM.png

Here’s a graph of the battery amperage taken by the controller. You can see the spike when I drove up highway 17 (again, 2/rds the way home). At the end is a spike to almost 600 amps as I hit the throttle all the way for fun at the apex of the hill before coasting downwards to my house:

Screen shot 2011-03-08 at 7.56.05 PM.png

It’s also interesting to see the spikes before the highway 17 climb; those were probably stop lights.


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So am I doing my math right that this works out to be roughly equivalent to 113mpg?



Small note: Watts are a measure of rate of power, not amount. Your units for the total capacity should be watt-hours and kilowatt-hours. So, 322 watt-hours / mile. Same for what you used: 6444 watt-hours, not watts/hour.

That’s pretty good range though, very cool.

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