Battery Temperature

Deutsche Version
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.

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.

Using emergency key to lock door when car is activated.

 The question is: If the battery temperature drops below the point were the car refuses to drive, will the high voltage system be operational to execute this method of rising the battery temperature?

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.

14of612, MINI E-collective, regenerating in it's alcove.

Guest entry on Tom Moloughneys blog

 Deutsche Version
Tom Moloughney, driver of #250, asked me to write a guest entry for his own blog.
Tom is the most active and most famous MINI E blogger and with almost more than 45.000 mi driven he has the highest mileage of the whole test-fleet.

I fulfilled Toms request  and gave a brief summary of the MINI E program in Germany.
The following will link to the page of my guest entry at Tom Moloughneys blog:

http://minie250.blogspot.com/2010/12/mini-e-driver-stefan-reitmeier-checks.html

MINI E in the snow

Deutsche Version

At the weekend I visited my parents again. After a 71km trip the charge level was reduced from 96% to about 25%, but I was pretty fast on the highway. During my stay I was able to recharge the MINI for about 6 hours at 12A/230V, which was sufficient to get the SoC to 86%.

Charging at 12A/230V in the heated garage

On the way back I visited an aunt. I was very relieved that I had chance to plug in MINI E for another two or three hours. So a achieved a full charged battery before driving home on the highway. Due to adverse weather conditions i drove moderately and reached home after 70km with little more than 20% SoC and 30km left.

I've parked the MINI at the return in the open, because on Monday I was not working and the garage was already occupied by the second car of the household.

MINI E 014 in the snow

The next morning the car was completely snowed. The outside temperature was -7°C, were the battery temperature was still at 16°C. After the trip the temperature was at about 35°C.

The following re-charging costs me 20kWh electricity of 20.7 Eurocents/kWh. Extrapolated to 100 km this are about 5.80 €. At the current diesel price of 1.30 €/l this corresponds to a diesel consumption of 4.5 l/100km for financial tie.