Monday, August 17, 2009

Baby it's hot outside...


And that means the battery packs in our electric MINIs are sweating just like we are. Last week, Chris Neff, a fellow MINI-E driver (#402), asked me if I had noticed any reduced range with the hot and humid weather. I told him I didn't, but would look closely at my mileage spreadsheet where I log all the trips I take, (yes, every time I drive the car) and keep track of the mileage driven verses the battery percentage used. I know it seems like a lot of work, but I'm so used to it, and now it's second nature. After looking at the recent data I was assured that I told him the truth, that my mileage wasn't suffering because of the weather. I guess he jinxed me because since then I have been noticing a distinct decrease in driving range. It has been really hot here in New Jersey lately, hotter than it's been all summer and accompanied by high humidity. The last few days now I'm seeing about a 15% reduction in range and that's not good. I need to have a range of 100 miles to feel confident I can accomplish what I need to during the day. My round trip from Chester to Montclair is only 62 miles, but I also need to drive around during the day as I own property in Florham Park and Oradell and sometimes need to go there without warning. This 15% reduction is really putting me right on the line of making it home at night or not. Where I was once comfortable with driving 110 miles on a single charge I'm now worried about getting 95. For example, today I have already driven 62 miles and I have 29% battery charge and a projected 27 miles remaining. I still need to drive home tonight which is 31 miles. I'll make it, I know I can push the car at least 5 miles further than the expected range provided I drive carefully tonight. The problem is, if it were cooler out, I would probably have 45-48% charge and a range of about 50 miles remaining and that's a big drop. Granted it's about 96 degrees out with high humidity, but I'm starting to think the car would have been better off it it were water cooled as opposed to air cooled as it is. Usually the battery temperature is between 85 and 100 degrees and lately I'm seeing battery temperatures of 105-113 degrees and that takes a toll on the batteries. I'm not an engineer, but I know enough about cooling to know that a good liquid- based cooling system would work better than the current setup. You need only look at Tesla Motors to see an example of an efficient liquid based cooling system. The battery pack in the Tesla Roadster is designed to have an average operating temperature of 77 degrees and a maximum operating temperature of 95 degrees. My MINI-E's batteries are operating at or over 95 degrees most of the time now that it's hot outside and the performance is definitely suffering. I'm also pretty sure the Chevy Volt will be liquid based as was GM's ill fated EV1. Perhaps MINI choose to do it this way to save time and get the cars on the road as fast as possible. After all, this car is a mule, pure and simple. It wasn't designed from the ground up as an EV, and I don't think BMW ever plans on selling electric MINIs. This car was made to test the components of the drivetrain for future EVs, not necessarily MINIs. I'm pretty sure when they do a ground-up EV design, the battery pack will have a more efficient means of cooling than what the MINI-E has - it better!

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