Battery cooling while Supercharging and AC

David99 said:

Very interesting and odd thing I just noticed. I charged my car at Barstow and I hear the AC compressor and fans running full speed after 20 min. I get in the car, turn on the AC and now the AC compressor and fans slow down significantly. I watch the charge rate but it's not going down. As soon as I turn off the AC the compressor and fans start kicking in again! That's not what I expected! That would mean the car switched off the battery cooling as I turned on the AC.

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Ive experienced exactly the same behavior. I had same question.

David99 said:

Very interesting and odd thing I just noticed. I charged my car at Barstow and I hear the AC compressor and fans running full speed after 20 min. I get in the car, turn on the AC and now the AC compressor and fans slow down significantly. I watch the charge rate but it's not going down. As soon as I turn off the AC the compressor and fans start kicking in again! That's not what I expected! That would mean the car switched off the battery cooling as I turned on the AC.

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Perhaps the car was using a fan only mode (that needed a lot of fan) to cool the battery when you had the AC off; when you turned on the A/C, it had coolant from the HVAC and did not need to run the fans as hard when using the active heat pump for cooling the battery.

I also suspect the algorithms are opportunistic: if the BMS realizes that cooling is needed, and there's mo other demands on the HVAC system, it will request all the cooling it can get to get the job done ASAP. If another demand (cabin HVAC), then it will balance the usage to satisfy both requirements, even though it may take longer to get the battery temp down, etc...

David99 said:

That sounds reasonable but it wouldn't explain why the fans and compressor slow down. If the battery cooling already needs such strong cooling it wouldn't slow down if cabin cooling is added.

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My point is that if there's no contention, the BMS might simply ask for 100% with the aim of getting the battery to a target temp in 5 minutes. If then contention arises (the cabin requires HVAC), then the BMS may defer, even if that means it may take 10 minutes to get the pack down to a target temp.

David99 said:

That crossed my mind. I did feel some vibration that I think was the AC compressor, but then it could have been just the fan. Not really sure how to be sure what is running. There is a lot of heat coming from the front when the fans are running that fast. I kind of doubt Tesla would make such a fundamental mistake. Sitting in the car with the AC running while waiting on a Supercharger is a common thing. I'm sure they thought of it.

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Here is a picture of the Temp control flows during a HPWC charge cycle while the battery was cool. Note the target temperature of 30˚C for passive cooling and 50˚C for active cooling. In this picture, because there is no cooling needed, the coolant is just circulated through the battery to keep all the cells at about the same temp. When in "series" passive battery cooling, I believe the valve on the left puts the battery in series with the charger, drive inverter, and motor (stator/rotor) cooling loops. In "active" mode, the "chiller" is used to actively cool the battery.

This is a picture from 5.9. In version 5.11, the "active cooling target" was changed to 49˚C, and the "active heating target temp" was changed to 9˚C.

Too bad "mere mortal" users can't see these screens. They would be great to watch in the heat and cold, charging, preheating, and driving. Right now these screens are only available when the technician connects to the ethernet, diagnostic port and enables them.

What causes the limiter to kick in? Is it Battery Temp, Inverter or motor Temp or all of the above.
Will not running AC help in cooling these components?

Thanks for sharing. I'd love to see this screen in action. I wish tesla would unlock this one.