At what temp does regen limit start?

wayner · Jan 8, 2016

My car spends the night in my garage which recently has been about 5C. When I leave for work there is, not unexpectedly a regen limit even though I turn the climate on 30 minutes before I leave and I try to end my nightly charge at 7am. But after about 15 minutes the regen limit goes away. My drive to/from work is typically 30-45 minutes.

I get to work without a regen limit and park in an underground parking garage - usually 3 levels underground. When I leave the garage in the evening my Tesla says that the "outside" temp is 10-12C. So my car has "cold" soaked at roughly 10-12C for about 9.5 hours. So shouldn't my battery be warmer than the ambient temperature in the garage?

The surprising thing is that on my drive home I have a regen limit, again for about 15 minutes or so. This must mean that regen limit kicks in somewhere around 15C - is that correct?

I would have thought that regen limits would only kick in under 10C.

Doug_G · Jan 8, 2016

I don't typically see any regen limits happening until closer to 5C, maybe 7C. But it depends on a lot of parameters - how warm was the car before starting cold soak, whether it's in the wind or sheltered (big effect), how long it's been cold soaking, etc.

When the pack is already above freezing, it doesn't preheat. It only preheats to a certain point, to a level that gives you about 30 kW regen (not clear what temperature that corresponds to).

wayner · Jan 8, 2016

My car is usually only outside while it is being driven. It spends the night (~13 hours) in a ~5C garage attached to my house plugged in to a HPWC. It spends the day (~9.5 hours) unplugged in a ~12C underground parking garage. It hasn't been that cold over the last two days - at worse -3. When I leave work at 6pm shouldn't the batteries be about 12C or higher, assuming they were warmer when they arrived at the garage due to heating up during driving?

So regarding preheating - does it still make sense to try to minimize the time between end of daily charging and your departure. I aim to end my charging at 7am as I usually leave home between 7:30 and 8 and higher electricity rates kick in at 7. (I wrote some code that accesses the Tesla API that sets the charge start time each day depending on the SoC.)

Kalud · Jan 8, 2016

The regen limit is based on actual battery temperature not outside temperature (although related after some time by thermal exchange). Based on leaked diagnostic screen its either 7C or 8C (it varies on firmware version). So if internal of the battery is bellow those, its marked as active heating and presumed regen would be limited.

llavalle · Jan 8, 2016

Kalud said:
Based on leaked diagnostic screen its either 7C or 8C (it varies on firmware version).

That would seem to agree with my own experience. I had a bunch of business trips and I left the car for a few days in my heated garage, each time setting the garage thermostat to a different temperature. Each time, the car had more than 48h for the temp to settle.

From the look of it, I get regen limits when temperature near the ground is around 8C (around 10C on my thermostat that sits around 5ft from the ground). Tested with 6, 8 and 10 and when I reached 10C, no more regen limits.

Doug_G · Jan 8, 2016

Good information. I had forgotten about the target temp from the diagnostic display.

I strongly suspect, though, that the preheat feature (via remote app) doesn't attempt to raise the temperature all the way to the target. In my experience it falls well short, even if you hit the preheat for another half hour.

wayner · Jan 13, 2016

This continues to happen to me every day. The car sits in a 10-12C garage for 10 hours or so and is regen-limited when I leave.

llavalle · Jan 13, 2016

wayner said:
This continues to happen to me every day. The car sits in a 10-12C garage for 10 hours or so and is regen-limited when I leave.

Put a thermometer near the ground, close to the battery pack. In my garage, it's a good 2-3C lower and I have really good insulation beneath my slab.

wayner · Jan 13, 2016

llavalle said:
Put a thermometer near the ground, close to the battery pack. In my garage, it's a good 2-3C lower and I have really good insulation beneath my slab.

I will try that but during the day I am usually on P3 of a parking garage that goes down to P5. I can see why the slab of my home garage would be a lot colder, but maybe not the office complex garage.

mnx · Jan 14, 2016

Kalud said:
The regen limit is based on actual battery temperature not outside temperature (although related after some time by thermal exchange). Based on leaked diagnostic screen its either 7C or 8C (it varies on firmware version). So if internal of the battery is bellow those, its marked as active heating and presumed regen would be limited.

View attachment 106983

8C is just where active heating starts no? I think the regen limit would start to kick in higher than that? ie. 10-12C?

llavalle · Jan 14, 2016

wayner said:
I will try that but during the day I am usually on P3 of a parking garage that goes down to P5. I can see why the slab of my home garage would be a lot colder, but maybe not the office complex garage.

Indeed. I did notice that with my relatively short commute (35km), the battery does not get hot enough to avoid the regen limit in the morning. But after being parked in the parking garage at work (which is a the same temps as my garage), while I still have the regen limit, it goes away after 4-5min of driving on my way back.

I guess what I'm trying to say is that thing (the battery) has a very high specific heat.

Kalud · Jan 14, 2016

mnx said:
8C is just where active heating starts no? I think the regen limit would start to kick in higher than that? ie. 10-12C?

Yes that's correct, I see regen limited between 60kW and 30kw when pack temperature is in the 10-11C region (measured inside the pack...)

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At what temp does regen limit start?

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