Charging and preconditioning in very cold conditions

[Titanium48]

My new-to-me 2016 SL arrived two weeks ago, I programmed the charge and climate control timers, and for the first week I woke up to a warm car with a nearly full charge, which gave more or less the range I expected in warm winter conditions (near 0°C). I didn't drain it completely, but an 80 km, mixed city and highway trip took it from 90% to 35%.

Then it got cold (between -20°C and -30°C this week). Using the charge timer no longer seemed to work and the car seemed to be unable to correctly determine the SOC - it would say 70-something % when I got in, but driving just a few km would drop it by 30%. The battery temperature gauge was down to one bar, so I figured that might have something to do with the electronic confusion and the failure to charge. Parked the car underground for a while to try to warm it up (got it up to two bars), then brought it home, turned off the charge timer and plugged it in. SOC was at 100% the next day, and there was no weird rapid drop (though as expected the range is down significantly), and since then I have been plugging in immediately after returning home and it seems to charge OK. The battery temperature has stayed at 2 bars, sometimes 3 immediately after driving.

Not using the charge timer seems to result in SOC in the high 80s after preconditioning though. I expected some loss of charge because I only have a 16A 240V EVSE, but 30 minutes at 4.5 kW is only 2.25 kWh, suggesting that no power was being pulled from the EVSE at all if that caused a 12% drop in SOC. I also manually preheated the car one day (plugged it in, turned it on, set the heat to 24°C and the fan on high), and after 20 minutes of that the SOC only dropped 2%.

Are these behaviors normal? Should I be doing anything differently?

 

[SageBrush]

I think pre-conditioning can max at ~ 6 kW and your EVSE is limited to about 0.9 * 16 * 240 = 3.5 kW (after accounting for losses.)

I'll guess that your funny SoC readings occurred due to battery temperature changes. If you can finish charging close to the time you use the car you should have a better experience.

EV ownership at -30C is an adventure. You are doing great !

 

[LeftieBiker]

I suggest you adjust your expectations in frigid weather, from a toasty warm interior when you get in, to an interior about 20-30 degrees (F) warmer, and a warm seat and steering wheel. The interior will feel plenty mild when it's that much warmer than the outdoors, even if it's "chilly" by the usual standards. Try 5-7 minutes of preheating. As for the SOC glitch, I've never experienced it, despite parking my 2013 Leaf outdoors for 5 Winters. That was with no or one battery temp bars.

 

[Titanium48]

That makes more sense if it uses 6 kW for preheating. I assumed 4.5 kW because that is the highest draw I saw when I cranked the heat to maximum manually. I'll try setting the timer a bit later and reducing the target temperature - I had it set to 25°C figuring that the warmer it was to start, the less heat it would need later, but if nearly half of preheating power is coming from the battery anyways it isn't actually helping.

Is the battery temperature gauge linear? Somewhere here someone said that bar 4 indicates a temperature between 50°F / 10°C and 74°F / 23°C. Extrapolating downwards, 3 bars would be -3°C to +10°C, 2 bars would be -17°C to -3°C and 1 bar would be -30°C to -17°C. If the battery heater is supposed to turn on at -17°C, a reading below 2 bars would suggest that the battery heater either isn't working, can't keep up with the rate of heat loss, or isn't turning on because the state of charge is too low.

 

[LeftieBiker]

The battery temp gauge is not especially linear.