michael said:
Do we know anything about the pre-soak? Based on what we are saying here, we seem to think the driving test itself takes an hour or two at most (50-100 miles at 50 or so MPH).
I would expect that the key advantage of the TMS is that it keeps the battery temperature within bounds prior to departure. In the ensuing hour or two, thermal capacity and insulation of the battery pack would, I imagine, not allow the battery to heat or cool dramatically.
So the test that would interest me (and I don't know whether or not the AAA test worked this way) would be to leave the car plugged in and charging for 8 hours at the test temperature, precondition the car to some stated temperature (also on mains power) and then run the test, also at the test temperature. I suspect one would see a smaller variation, particularly at low temperature.
And the cabin HVAC conditions should be noted.
I've sort of "run the test" that would interest you and my results are in line with the AAA results:
I leave my car plugged in overnight in an unheated detached garage, with a go-time preconditioning set for my morning departure. My morning drives have been at 20f or below pretty much from December to last week. Cabin heating is set to 66f when I start the car.
My starting range is 45-50 miles, whereas same driving gets me 90-105 in the summer without AC. So that's a 50%-plus drop. Yes it's a guess, and I don't drive down to empty in winter to see if the guess is accurate, but I do drive down to 50% SOC using ~24 miles so I think the guess is pretty accurate.
Two thoughts about this observation:
1. The key reasons AAA and I see such dramatic range reduction in these very cold conditions are that we use cabin heating, and we do city driving. In "normal" conditions when cabin heating is not engaged, city driving is extremely efficient-- minimal energy use occurs while the vehicle is stopped in traffic, little energy is used when driving at modest surface street speeds, and regenerative braking kicks in often. But when cabin heating is engaged, city driving becomes quite inefficient. There is a significant constant draw, whether stopped or moving. In fact, the slower one drives, the larger the effect of cabin heating on efficiency. Say the heater draws 6kW. Over an hour it's used 6 kWh. If you drove at 30mph for that hour, the motor used about 175Wh/mi or 5kWh in the same time. So the heater took more than the motor did, and your range would have been cut by more than half. If you drove 55mph instead, your motor used about 250Wh/mi or about 14kWh in an hour, so your range would have been cut by only a third.
2. Honestly I think the degree of range loss in very cold weather is similar whether or not the car is left on plug to keep TMS active. My amateur understanding is that TMS isn't there to improve or maximize cold/hot weather range. It's there to maximize battery lifespan. These might seem related, but they're really not. In cold weather, TMS only keeps the battery warm enough to be able to charge safely- if charging is attempted on very cold batteries, they can be permanently damaged. In hot weather, TMS only keeps battery cool enough to charge safely- if battery gets too warm, it ages prematurely and range degradation is accelerated. So I'm not sure why the AAA and / or USA Today would be surprised that cars with TMS feature are affected as much by cold as those without.
