Saturday, August 13, 2011

A Case of the Creeps?

There's a hill at the end of my street and the car rolls backwards a bit when a release the friction brake if I don't activate the anti rollback feature. A simulated transmission creep would eliminate this.

There are a lot of differences in EV's and internal combustion cars. The fuel used to propel the vehicle is obviously the biggest difference, then the different sound and feel of the electric drivetrain followed closely by the regenerative braking which, if strong like it is on the MINI-E, can take a bit of driving to really get used to.

Then there are the less obvious differences like the single speed gearbox. Shifting gears is not necessary so it is like driving an automatic transmission car, however when you stop, the car will roll forwards or backwards if you are on an incline or decline like a manual transmission car would if it wasn't in gear and your foot wasn't on the brake pedal.

Virtually every car with an automatic transmission built in the past four or five decades has had what we have called the idle creep feature. Anyone that has driven an automatic transmission expects the car to slowly move forward when you release the brake pedal even if they don't depress the accelerator. This feature is useful when you are stopped on an incline as it helps the car from not rolling backwards the instant you release the brake. It can also be helpful when parallel parking. By slowly moving forward without needing the depress the accelerator, the driver won't run the risk of lunging forward too quickly and perhaps hitting the car in front of you when squeezing into a tight parking spot.

Yet, despite the benefits of having "the creep" most EV owners I know say they don't want it on their EV and implore auto manufacturers not to copy ICE vehicle features when they design their EV's. I don't necessarily want them to omit features just because by doing so it will keep EV's "pure". If the feature makes the car better than put it in, but if they are putting it in just to make the car more familiar to the drivers, than I'm not sure I'm in favor if it. The real question is do current EV drivers and potential future EV owners want it? That's what I'm interested in hearing. So what do you think? Do you want the creeps?

Please enter your vote on the poll at the top right side of this blog and leave a comment to explain why you voted the way you did. 

Saturday, August 6, 2011

Some Like it Hot - The MINI-E Does Not!

The outside temp read 107 and the MINI-E's batteries were a sweltering 114

It's not too often that it is so cold or so hot outside that the primitive thermal management system of the MINI-E really can't cope with it, but it has happened a couple of times in my two years with the car.

I should remind everyone that this is a prototype EV and it was designed for research, so don't think production electric cars will be this susceptible to weather extremes. Most all EV's that you can either buy now or will be able to in the near future have a complex thermal management system, capable of keeping the battery pack at optimal operating temperature regardless of the ambient temperature, so you won't have to worry about overheating problems like I do. The BMW ActiveE, for instance, the MINI-E's successor, will have such a system and it's one of the features I am anxious to try out.

Temperature warning icon
So getting back to the heat wave we recently experienced here on the East Coast, we had a solid week of high 90 degree and even a few days of 100+ degree temperatures. On one particular day, I was in a bit of a rush and had about 50 miles of highway driving to do. I had the air conditioning blasting as you might expect, and was tooling along at 70-75 mph when I noticed the battery temperature warning light came on. It's really not a big deal, but the car is telling you it's time to monitor the battery temperature because the modules are getting really hot. Just by slowing down to about 60 mph I kept the temperature from getting any higher but it wasn't going down either. If I had continued to drive at 75mph, I'm sure it would have continued to get hotter.

Once I finished my journey I returned to my restaurant and plugged in. I was pretty low on charge, around 10% and needed to get up to about 35% to get home later in the day, but since I had about four hours, that should be no problem. In normal conditions, I would be charged up to 35% from 10% in about 45 minutes, as I have a 50amp EVSE at my restaurant, capable of charging at 12kWh. However, this wasn't normal conditions, and when I checked the charge level about three hours later, it was only up to 20%! Now I was starting to worry because I really wanted to get home as we were having guests over for an evening BBQ and swim and I didn't want to be late. I reset the charge rate to 12 amps, thinking the car may accept the lower amperage and charge rate. The reason the car wasn't charging is because when you charge or discharge batteries, the chemical reaction causes them to get hotter and the car is monitoring the battery temperature and basically saying they batteries are too hot already, so it's not allowing it to charge, especially at such a high rate because that will only get them hotter.

Anyway, either the lower charge rate worked, or by sitting for a few hours the batteries cooled down enough to allow charging and the car charged up to 32% in the next hour and that was enough for me to make it home on time. In all my time with the car this was one of the few times that I ever wondered if it would let me down and prevent me from getting to where I needed to go. Once home I plugged in and left the car alone. The next morning it was fully charged, however I don't know how long it took or if it was charging slowly because of the temperature, though I suspect it was.

One of the major reasons you wouldn't want your EV's batteries to get this hot is that the excessive heat will prematurely degrade the cells and you will eventually have to replace the pack sooner than if the temperature was kept at optimum temperature, which is roughly 75 to 95 degrees Fahrenheit. If thermally managed to keep the batteries at these temperatures, the cars range will be optimized and the life of the batteries will be extended. However the life of the MINI-E's batteries aren't really an issue for us, as the MINI-E trial lease program will end soon, giving way to the BMW ActiveE program which will ultimately lead to the 2013 BMW i3. Personally I think BMW intentionally left the MINI-E without any sophisticated thermal management to test the effects of the weather extremes. It's all part of the learning process. These cars are such a departure from the major automakers comfort zones, they really need to comprehensively test every aspect of the electric power train before they even think about putting an electric car in their showroom for sale.