ripple4 wrote:with this battery cooling idea, its not clear how much heat it will need to remove and how quickly. I suppose charging is the scenario to consider and taking a stab at it with a 85% L2 charging efficiency the heat put into the 24kwh pack with a 6.6kw charger would be .5kwh/hour or 2000 BTU/hour and 1/2 that for a 3.3kw charger in a base/early model.
Driving matters as well, perhaps even more than charging. Depends on how you drive and charge.
Power lost in battery is very roughly current squared times series resistance. I^2 * R
Current is power divided by voltage. W / V
Voltage is about 350V to 400V, varies over SOC.
Resistance varies from about 0.1 ohms to about 0.35 ohms, depending on age, direction of current and more.https://avt.inl.gov/sites/default/files ... af0356.pdf
So with a full power discharge, might be 18kW. Think driving very fast up a very steep hill. Or could get close to that with repeated accelerations and regenerative breaking. (80kW discharge followed by 55kW charge). Round the Nurburgring.
However, unless you are driving round the 'ring, anything close these numbers can't be sustained. So you need a model as to how the car is used.
Suppose you L2 charge for a hour once a day, and drive at a reasonable power for a reasonable commute. Then you get to no cooling, unless the outside air temperature is averaging over 30C or so.
Or you could do a road trip model. Driving at x power, DCQC, repeat. In Kansas in the summer, at 45C. Or Nevada, or Death Valley. Or something like that.
Remember that preventing condensation at any time, coolant leakage even in the case of an accident and mechanical stress under all conditions on the cells are all more likely important.
As a road trip example, I recently did a 160 mile trip with 2 DCQC sessions, total time of 5 hours including stop at the midpoint. Battery temperature went from 18 C to 36 C at the end of the trip. Ambient was about 20 C plus minus 2 C the whole trip.