From the MINI E-team I got an e-mail that says: When the battery temperature drops to 5°C (41°F) or below, the MINI may not start.
Driving the car for a longer distance means rising the battery temperature to higher values. Driving the car regularely avoids dropping the temperature to critical values due to the slow cooling-down of the battery pack.
My daily commute is only about 20km (12.5 mi) in total. That means for the single trip with a distance of 10 km (6,2 mi) a gain in battery temperature of 2-3 °C (5-7°F).
At ambient temperatures of -7°C (19°F) i had typical battery temperatures of 2°C (35,5°F) with the car parked in the unheated garage. Driving to work results in a battery temperature of about 5°C (41°F) before leaving the car for the next 8-9 hours in the parking structure which causes again a drop in battery temperature to 2°C (35,5°F). Now i'm avoiding the open park decks over the ground and hiding the MINI E in the basement expecting more pleasant ambient temperatures.
So with this situation I really have a little problem now, because I can not ensure higher battery temperatures and this may go worse when the ambient temperatures fall.
At battery temperatures of 1°C (34°F) and below the MINI refuses to charge. In this case you have to drive the car until the battery temperature rises or you have to install an additional heater powered by a separate wall socket.
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| Battery to cold for regenerative braking. This indicates also, that charging may not be possible. |
Yesterday I had a battery temperature of -2°C (28,5°F) with an SOC of 20%. I was driving a short distance just to ensure that the car is still operational except regen was completely disengaged.
I parked in front of the garage but still outside and let the car activated with the cabin heater at full power and the fan at second setting. This method has two effects: Activating the battery with the high power consumption of the cabin heater. And venting the battery with warm air from the cabin.
After one hour I returned and the battery temperature was 8°C (46°F) and SOC about 15%.
Because running the heater affords activation of the high voltage system I had to let the key in the car. I locked the car with the emergency key, so this could be done at a public place if necessary.
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| Using emergency key to lock door when car is activated. |
After that I charged the MINI at the wallbox with the 32amp-setting, but still outside the garage.
The next morning the car was still charging. Although the car had spent about 11 hours connected to the wallbox, SOC was only at 75% and battery temperature dropped to 3°C (37,5°F). This was not the first time I noticed a significant reduction of the charging rate when the battery temperature is low.
The self generated heat when charging at 32 amp is not sufficient to rise battery temperatures to an optimum level at low ambient temperatures. So a fully charged battery at 3°C (37,5°F) cannot store the same amount of energy as it could at 20°C (68°F). This leads to the often discussed range limitations at cold weather. In addition to this the extensive use of the cabin heater intensifies the effect.
Keeping the battery at convenient temperatures with an additional heater like Jim McL did is the best solution for the MINI E to face low temperatures when full range is needed.
Compared to the beginning of the test now I connect the car to the wallbox every day to keep the SOC as high as possible to have more energy left in case of "off grid self heating" is necessary.
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| 14of612, MINI E-collective, regenerating in it's alcove. |
Nice report! I see you're learning how to keep the car going through the winter months. I had to learn that out for myself last year, but now I have a good system to maintain proper battery temperature.
ReplyDeleteI guess this is why BMW calls us "pioneers"
Happy New Year from the US!
Stefan
ReplyDeleteI never had the car refuse to drive from being cold. I does refuse to charge or regenerate during braking when really cold. But I had the impression that it would drive even at battery temperatures as low as -25 C.
Thanks for the link to my blog. Tom took me off from his links!
Jim McL
Jim,
ReplyDeletei agree that common li-ion batteries should work even at very low temperatures. There is some significant power-loss due to the increased internal resistance, but they should work down to temperatures until the electrolyte will freeze. But then the battery is already destroyed.
Charging of common li-ion batteries is possible only at temperatures above 0°C.
I think, MINI Es batteries behave in a similar way and I hope there is not some feature that prohibits the use of the car below a distinctive temperature.
I was reading your blog describing the electrical issues with great interest.