Battery Heating/Cooling

[ajdelange]

Newbie here who hasn't taken delivery yet (soon) trying to learn as much as possibly before the car arrives. The battery pack has to be heated when the weather is cold and cooled when it is hot. Cooling is handled by a compressor which cools glycol circulated through the battery pack, the motors(?) and the inverters(?). That same compressor presumably cools the cabin by, presumably, sending that same glycol through a liquid to air heat exchanger. Is that correct?

The real question regards heating. Is that done by using a separate resistance heater or by running the compressor as a heat pump which sucks heat out of the air and transfers it to the glycol? Seems to me that in moderate climates at least that would result in more BTU per kWh than straight electric heat (and thus less impact on range) as the COP can never be less than 1. Anyone know the answer to this?

 

[Rocky_H]

Tesla does not use a heat pump for cabin heating. It's always a resistive heater.

 

[ajdelange]

Is that separate from the heater used to warm the batteries?

 

[xyeahtony]

Is that separate from the heater used to warm the batteries?

the battery has its own heater to warm itself as far as i know. In practical sense, the battery does not actually need to be "heated" in order to function. You do need a warm battery though in order to have regen and peak supercharging speed though, but the car can and will still drive on a normal cold battery. People in norway get far harsher winters than we do in america and their teslas still function fine.

Model 3 battery packs don't even have a dedicated heater, they rely on waste heat from the drive unit to warm the battery. so tesla has already determined that heating the battery isn't the biggest deal.

But yes, this is why electric cars use more power in the winter (but gasoline cars do too). In the cold, more energy is needed in general to reach optimum operating temperatures.

 

[gnuarm]

the battery has its own heater to warm itself as far as i know. In practical sense, the battery does not actually need to be "heated" in order to function. You do need a warm battery though in order to have regen and peak supercharging speed though, but the car can and will still drive on a normal cold battery. People in norway get far harsher winters than we do in america and their teslas still function fine.

Model 3 battery packs don't even have a dedicated heater, they rely on waste heat from the drive unit to warm the battery. so tesla has already determined that heating the battery isn't the biggest deal.

But yes, this is why electric cars use more power in the winter (but gasoline cars do too). In the cold, more energy is needed in general to reach optimum operating temperatures.

To say the model 3 uses "waste" engine heat to heat the batteries is not quite correct in that they will use the engines as heating elements even when not running such as when preconditioning.

Not sure what you mean by "heating the battery isn't the biggest deal". Heating the battery is important to battery life. When cold the battery has limitations and heating the battery deals with those problems. I don't think using the motors to heat the battery in any way reduces the significance of this.

 

[ajdelange]

I haven't been able to discover much beyond that there is a glycol loop that runs through the motors and the battery pack (and I'd be surprised if the IGFETs or IGBPTs aren't on a cool plate in that same circuit. That loop has cool glycol circulated through it in warm weather and presumably that glycol is cooled by running through a heat exchanger whose other side is an evaporator supplied with liquid refrigerant from the compressor whose high side is, I would guess, run into a "radiator" exposed to the outside air.

In cold weather when the battery must be heated (but I wouldn't think the motors or transistors need to be) it would seem logical to flip a reversing valve and transfer heat from the cold air to the battery. Note that this wouldn't work in very cold weather and I assume that's why there is a cold weather option on the cars. But down to say 45 °F you ought to be able to get about 3 watts of heating for every watt of electricity used and I would think that in a vehicle that tries to spare every watt for range this would be a viable approach.

 

[Rocky_H]

@ajdelange Yes, to using radiators to cool the fluid to the outside air temperature in hot weather. And as needed, when the radiators can't cool it enough, (like many degrees over 100 Fahrenheit), it can change some valves to actually use the air conditioner to chill the glycol liquid before sending it through the battery.

No, they don't have that reversability built into their air conditioner system, so they can't use it as a heat pump ever. For the S and X, they have an inline resistive heating element that can heat that glycol directly. On the Model 3, it doesn't have that separate battery heater. It primarily uses waste heat from the motor. There has been a description listed that while parked, the car can run current through the motor windings, but so far, I don't think any owners have been able to definitively see whether that is being used yet or not.

 

[SSedan]

the battery has its own heater to warm itself as far as i know. In practical sense, the battery does not actually need to be "heated" in order to function. You do need a warm battery though in order to have regen and peak supercharging speed though, but the car can and will still drive on a normal cold battery. People in norway get far harsher winters than we do in america and their teslas still function fine.

Model 3 battery packs don't even have a dedicated heater, they rely on waste heat from the drive unit to warm the battery. so tesla has already determined that heating the battery isn't the biggest deal.

But yes, this is why electric cars use more power in the winter (but gasoline cars do too). In the cold, more energy is needed in general to reach optimum operating temperatures.

I suggest you do a little research you are way off. Oslo average temps look to be on par with Chicago. There is a LOT of USA north of Chicago.

Cold weather definitely presents some challenges with EVs. I have a short commute near Green Bay battery and cabin warming do not really level off while driving unless I preheat from the home hookup heavily.

That said the INSTANT heat from the cabin resistance heater is an awesome feature and so easily accessed from the app. I had a car with OnStar before this and the Tesla app is so much better and quick to respond.

In places with real winter I strongly suggest HCWC with as much amperage as the car can handle because it is a good way to warm the battery while charging before you leave in the morning.

Honestly though in Virginia it isn't going to be a big deal

 

[xyeahtony]

I suggest you do a little research you are way off. Oslo average temps look to be on par with Chicago. There is a LOT of USA north of Chicago.

Thanks Mr. Internet Fact checker, anyone who's watched Bjorn's Tesla youtube videos knows exactly how cold it can get in Norway. I'm quite aware there is a lot of USA north of chicago, i live in New England. But that wasn't even the point of the post at all, i was just saying it gets colder than where the OP lives and plenty of EVs do fine.

Regardless of where is colder, maybe i should reword then. Plenty of places in America get colder than Virginia and Teslas still work there fine.

Happy?

To say the model 3 uses "waste" engine heat to heat the batteries is not quite correct in that they will use the engines as heating elements even when not running such as when preconditioning.

Not sure what you mean by "heating the battery isn't the biggest deal". Heating the battery is important to battery life. When cold the battery has limitations and heating the battery deals with those problems. I don't think using the motors to heat the battery in any way reduces the significance of this.

It means the car can still drive even with a cold battery, so its not something anyone has to worry about in terms of vehicle function. Heat is a bigger killer of battery than cold, which is why the model 3 battery has active cooling but no active heating elements.

 

[ajdelange]

I did find a posting that showed a diagnostic diagram from the 3 and another video where they went over the temperature management system. It is evidently quite sophisticated. I did not see anything that led me to conclude that the compressor refrigerant flow was ever reversed i.e. that the compressor was ever used to warm anything. Evidently there is a 6 kW electric heater in there. That's over a ton and a half of heating. Each hour it runs only takes about 18 miles out of the range so I guess they saw no need to complicate things further than they already are.

 

[David99]

Newbie here who hasn't taken delivery yet (soon) trying to learn as much as possibly before the car arrives. The battery pack has to be heated when the weather is cold and cooled when it is hot. Cooling is handled by a compressor which cools glycol circulated through the battery pack, the motors(?) and the inverters(?). That same compressor presumably cools the cabin by, presumably, sending that same glycol through a liquid to air heat exchanger. Is that correct?

The real question regards heating. Is that done by using a separate resistance heater or by running the compressor as a heat pump which sucks heat out of the air and transfers it to the glycol? Seems to me that in moderate climates at least that would result in more BTU per kWh than straight electric heat (and thus less impact on range) as the COP can never be less than 1. Anyone know the answer to this?

There is no heat pump, but the car will use heat losses from the motor, inverter, charger and DC-DC converter and redirect it into the battery via the coolant if the battery is cold. It works pretty well. The battery also warms itself up by being used. Ohmic losses generate heat inside the battery when you drive or charge.

Only when the battery is very cold, the dedicated battery heater will kick in. This is important when the battery is below freezing. A Lithium battery would get damaged if you charge it below 0 Celsius. Discharging (=driving) is fine though. This heater shuts off again once the battery has reached aprox 10 Celsius. In the winter, it is a good idea to use the charge timer and charge the car so it just finished before you leave in the morning. Charging warms up the battery. This way, when you leave in the morning, you have a relatively warm battery.

 

[gnuarm]

It means the car can still drive even with a cold battery, so its not something anyone has to worry about in terms of vehicle function. Heat is a bigger killer of battery than cold, which is why the model 3 battery has active cooling but no active heating elements.

Yes, the car can be driven when the weather is cold. I don't think anyone ever disputed that fact. The car can be driven when it is hot as well. The batteries are actively cooled, so all is well. It doesn't matter which is the bigger killer, cancer or heart attack. It is wise to avoid both.

I was only asking a question.

 

[gnuarm]

I did find a posting that showed a diagnostic diagram from the 3 and another video where they went over the temperature management system. It is evidently quite sophisticated. I did not see anything that led me to conclude that the compressor refrigerant flow was ever reversed i.e. that the compressor was ever used to warm anything. Evidently there is a 6 kW electric heater in there. That's over a ton and a half of heating. Each hour it runs only takes about 18 miles out of the range so I guess they saw no need to complicate things further than they already are.

I love it when people casually use that four letter word... "only". lol

Everything I've read is that the model 3 does not have a separate resistive heater. The 6 kW heater is in the S/X. The model 3 uses the motors as heaters even when the car is still. My understanding is it takes more than an hour to fully heat the battery with this heater. In fact, I believe I have seen that the heater will come on to keep the battery from totally freezing when in extreme cold. That's another reason to leave the car plugged in all the time.

Something Bjørn Nyland mentioned in a very recent video about winter charging is that the Teslas seem to have thermally insulated batteries while other cars don't. The result is the Tesla does a lot better in the winter than the others which even after driving some distance won't charge at a full rate.

I believe I've seen my X run the battery heater while driving. I just drove 1000 mile trip and I'm pretty sure I saw the consumption go up to 600 Wh/mi for no apparent reason several times for around 4 or more miles at a stretch. If that's not from heating the battery what else could it be? The terrain was not uphill for 4 miles. Also the edges of this increased power was sharp. It's like what I see every time I drive the car after being parked for an hour or more.