cell warm up analysis

[howardc64]

Sorting out coolant heater behavior with a fellow 2013 MS owner with gen1 DCDC in these winter months. Used scanmytesla to record 3 trips. Here is the conclusion and data

• Car is no hurry to warm up the cell. Regen is limited for quite while until avg cell temp reach ~18.4C which takes more than 1/2 hour. Maybe Tesla software looks at cell with min temp rather avg.
• Coolant heater is completely off during all 3 drive cycles of 30-45min each. Software seems to decide... hey you are using the stator and it will warm the battery and i'm in no hurry, so warm slowly as you go
• M3 has no coolant heater and warm up battery by stator and cell discharge/regen alone. Looks like MS is using similar logic.
• Remember there is nearly 1000lb of battery down there needing to get warmed. Probably no quick heating solution anyways.
• Only time I've been able to get coolant heater to turn on is in garaged, plugged into L2 charger and use app to max defrost (see here). During drive, turning on rear window defrost (will self turn off anyways) and windshield on max AC+fan speed doesn't seem to trigger the coolant heater to come on.

If anyone see different. Please share.

All 3 trips graph here

• Ambient temp is about 30F
• 2022-12-01 trip1 is 45min drive out and back in 1 drive cycle. Battery was charged 60mi @ L2 30A a few hours prior so ~12C starting out.
• 2022-12-02 trip1 is 30min trip to local Toyota dealer to buy parts for Tesla (wish I was joking but acquiring parts from Tesla require monk zen level patience)
• 2022-12-02 trip 2 is 30min return trip from local Tesla dealer to home
• BMS max charge is basically regen limit. Slightly lower than Tesla's display but tracks
• Really big BMS max charge drop is going down big hill near my house

So looks like coolant heater is just for

• Mostly to prewarm the battery before the trip if you request it
• On gen1 DCDC's location, probably mostly sit there with easy moisture intrusion, fail, fail HV safety check and disable car from driving. See here

 

[howardc64]

Another interesting observation. When starting trip out fairly cold (cell and stator ~< 10C) Thermal system stay in parallel for 10min rather than series mode. Quite interesting. See 2022-12-02 trip1

LDU wants to keep its heat rather than share with battery? haha

Thermal circuit diagram link

 

[dark cloud]

Makes sense, not using the heater maximizes efficiency. The model 3 even has the coolant go through the computers to draw the wasted heat, if I'm not mistaken.

Climate control without max defrost does turn on the battery heater. You have to wait about 30 seconds to see the squiggle bars on the app, but definitely I get more regen than if I don't heat the cabin before departing. But we were looking at this stuff last year and the year before, and every software update changed what you thought you knew about the car

If you wanted to "cheat" and make sure the coolant heater comes on navigate to a supercharger. The minimum distance for this to happen seems to have increased over the past few years, and there are so many around now if one lives in a large city it is pretty easy to find one within 20 miles of where the car is it.

 

[dark cloud]

Climate control without max defrost does turn on the battery heater. You have to wait about 30 seconds to see the squiggle bars on the app,….

Took 48 seconds this morning to be exact

 

[howardc64]

Makes sense, not using the heater maximizes efficiency. The model 3 even has the coolant go through the computers to draw the wasted heat, if I'm not mistaken.

Climate control without max defrost does turn on the battery heater. You have to wait about 30 seconds to see the squiggle bars on the app, but definitely I get more regen than if I don't heat the cabin before departing. But we were looking at this stuff last year and the year before, and every software update changed what you thought you knew about the car

If you wanted to "cheat" and make sure the coolant heater comes on navigate to a supercharger. The minimum distance for this to happen seems to have increased over the past few years, and there are so many around now if one lives in a large city it is pretty easy to find one within 20 miles of where the car is it.

Very cool, makes total sense. Sorry I'm 1-2 year late to the party. Seems to always start digging "after" warranty honeymoon. Leaking LDU coolant seal kind of forced my hand to dig deep into the Gen1 Model S haha.

Took 48 seconds this morning to be exact

Cool, never quite had the patience to listen to full defrost fan blast for more than a second Good to know!

So I think the summary still holds... coolant heater is mostly dormant and (jokingly) serves to disable drivability haha (am studying the water intrusion path from windshield above gen1 DCDC)

 

[PCMc]

Just a couple comments.

If I'm reading the three charts that OP posted battery average temp starts at about 12~15C ... about halfway between 0 and 25 and presuming plot is in deg C given OP's reference to other values in degC. That's a much more important value than any reference to 30F / 0 degC ambient for this test.

12~15C starting temp for the battery is actually not a very extreme case and the fact the battery heater is not being used in these cases really should not be of any surprise. A much more telling test would be to park the car outside for 24-48 hours in somewhere between -10 to 0 degC and I expect you'll see a dramatically different behavior. I know from my own personal experience taking road trips with my car through the NE US, including overnight stay in the Rochester area around 0 F / -17ish C you see very high energy consumption shown on the trip meter at first as all the heaters are going to max.

If your objective is range, which means minimizing energy usage, then actually not trigger heaters unless you absolutely needed to maintain battery cell health is actually very desirable way to design the system controls. Letting the system warm up passively due to energy dissipation from operation tends to be the most efficient. Yes, you may have less regen capability, so less energy recover, but in many drive cycles, letting the system warm up passively is still the most overall energy efficient approach.

Just my two cents.

 

[gillmj24]

Derp. I thought the squiggles next to the battery meant a seat heater was on LOL

 

[rsg123]

Derp. I thought the squiggles next to the battery meant a seat heater was on LOL

That’s kind of Tesla’s fault for using the bacons for both of those icons.