Monday, January 31, 2011

Thermal Conditioning for the Battery AND the Passengers!

The Cog & Temp icon you see it telling me the battery is too cold and the car will not have regenerative braking. I see this when the battery temperature gets in the low 40's. If the battery temperature gets any lower and the car will not accept a charge.

There's a lot of talk about thermal conditioning in electric cars, and for good reason. Maintaining proper battery temperature will not only help the vehicle to offer a more stable, predictable driving range, but will most likely be a big factor in determining how long the battery will acceptably perform before a replacement is needed.

The MINI-E is a wonderful vehicle. Those that have followed this blog know how I feel about it. I think the electric propulsion system pairs so well with the small, fun to drive MINI Cooper, that it's an outright shame BMW isn't going to offer it for sale in the near future, yes it's THAT good. All that said, the MINI-E is a prototype test vehicle and it does have it's faults. The most glaring shortcoming, is a lack of a proper thermal management system. The passive, cabin-air based system is insufficient to warm the pack in the winter or cool it off in the summer months. If the ambient temperature is below 95 degrees or above 50 degrees, everything is just fine and you can almost always squeeze out 100 miles of range if you drive conservatively, even 120-130 if you stay off the highways. However once the temperature extremes occur, the car lets you know it's not a happy camper. I'm going to focus here on the cold weather effects, since I did a post last summer about my hot weather experiences and difficulties.

The most obvious problem is the reduced range. I'm not really 100% sure if the battery simply cannot store the same amount of energy, or if it cannot efficiently use it when it gets cold, but the reduced range that the MINI-E has in the cold Northeast is something that you have to accept and manage. I know that it's not only the batteries storage/usage of the energy, but also the fact that the cabin heater uses a good amount of juice so it's really a double hit that conspires to cut into how far the car will go. This winter has been very cold and there are days when the temperature doesn't even approach 20 degrees Fahrenheit (-7C). On these days I'm lucky to push the car to 75 miles per charge. That's about a 30% reduction from optimal conditions, and in my opinion, it's just too much for the average retail consumer to accept.

That's -2 degrees!
Luckily, there is a better way to manage the battery temperature and thus the range, and that's by implementing an active thermal management system to heat and cool the battery as needed. These systems will obviously add to the cost to the vehicle, but in my opinion, it's money well spent. BMW seems to agree with me because their next EV offering, the 2011 BMW ActiveE will have active thermal management. I expect to be one of the few people driving an ActiveE this summer when the MINI-E program ends so I'll be able to report on how well the system does or doesn't work. This to me is the most important improvement that BMW can make from lessons learned in the MINI-E program.

MINI-E winter driving apparel !
There is one more thermal conditioning issue I need to bring to light. That's the MINI-E's inability to thermally condition it's passengers! There's no problem in the summer as the A/C works fine. However when it's cold outside, the MINI-E drivers here on the East Coast are cold also! The heater in the car is woefully insufficient to really warm the cabin or it's passengers. Those of us that have a MINI-E in NY & NJ have learned to deal with it, but it's not fun. Most all of us have learned to keep gloves, a hat and a blanket in the car at all times. Others have even used a hot water bottle(Now I know why BMW calls us pioneers!) I haven't done the hot water bottle thing, but I do keep a hooded sweatshirt, gloves and yes, a small blanket in the car especially when I drive home from work late at night when it's bitter cold outside and the car has been sitting outside for 12 hours.

My Garage Heater
Last year I did a post about installing a heater in my garage to keep the car warm overnight. It's works really well and even keeps my family room warmer because that room is adjacent to the garage. I set it at about 45-50 degrees so no matter how cold it gets outside the garage is around 45 degrees.  Recently I have also been pre-heating the cabin in the mornings. I have a small ceramic heater that I put in the cabin about 30 minutes before I leave for work. When I leave the cabin is very warm and I don't need to turn the heater on for a while and that helps to extend the range a bit. This is similar, but not as good as preconditioning, something all production EV's have the ability to do.

It's going to be really interesting to see how much better the BMW ActiveE manages the weather extremes. I trust the engineers over in Munich know what they are doing. I'm sure I'll be writing a lot on this issue once I've had the time to drive the ActiveE in the extreme weather and analyze my range data. It will be nice to use the MINI-E as a comparison vehicle as I write about the ActiveE. Hopefully I'll be using the word "improvement" a lot, but you never know...


  1. Thanks for another very informative post! I take it that as a proponent of active thermal management you won't be looking at a LEAF, and that you'd also advise folks in cold weather climates -- Colorado, for instance, where it's currently -1 Fahrenheit and dropping -- to go for an EV with thermal management over one without it.

  2. Christof,

    I am concerned about the LEAF's passive system in cold weather climates, but there is a big difference with the LEAF and the MINI-E. The LEAF was engineered by Nissan to be sold to the general public and the MINI-E is a basically a test mule. BMW didn't even make the components used in the car and knew they were never going to actually sell it.
    So in that regard, it's not really fair to compare the LEAF's thermal management with the MINI-E's. If I wanted to buy a LEAF, I would wait until I got some feedback about how well it performed in my area before I bought one though. It won't take long once some people in your area that buy one start talking about how it's working out. I'm sure it will perform better than the MINI-E in the cold, how much better is the question.

  3. Nice post. I wonder if they purposely used an underpowered cabin heater to use less energy or if they just didn't have many options.

    Regular cars just use the excess heat from the engine to warm up the passengers, but with electric cars that becomes a problem because there is very little wasted heat, not nearly enough to use to heat the car up.

    One positive that electric cars have is that the heater will start to work instantly. You do not have to wait for the engine to warm up before you have heat for the passengers.

  4. Hi Tom, I just read your Plug In Cars post. GREAT JOB!

    We need more people like you with real life electric car experience to speak the truth about them. The reporters that bash them really know NOTHING about EV's!

  5. Hey Tom

    I read them talking about you over at, but the link went nowhere. Good for you, calling that author out.

    But you took my blog of your link list?

    Was that post about the need for three power inlets to crazy for you?

    Jim McL

  6. Jim, I needed space and removed the links of people that returned their cars figuring that they would no longer write about the MINI-E.
    I'll reinstate it for sure if you want!

    As for the article, did yo read what he wrote about EV's being unsafe in the winter? They'll leave you stranded, you'll get frostbite when the battery dies! Really???