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Model 3 Battery Heating?

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I leave my M3 plugged into 240v dryer socket in garage. With climate control off, outside temp 20F, garage temp 50F, house temp 70F, I woke up one morning to cabin temp of 85F. I turned on climate control to LO to cool cabin to 75F and then turned Climate off and unplugged and cabin eventually cooled even more. The car sits in garage several days between usage. Should I not be leaving it plugged in all the time? I keep the battery charged to 183 miles on a 310 battery.

Always leave your car plugged in if you have the ability to. There is never a case where it's better to be unplugged.
 
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tesla-app-heating-icons-png.351170


Defrost, heated seats, battery

NICE...that is a Model 3 though right? I've been waiting to see something like that...do you know at what ambient temp that triggers at?
 
One of our Model 3s is entering its second winter season and the others are experiencing their first cold season. I’ve never seen any evidence of active battery heating on these cars. The battery only seems to get warmer from resistance heating when driving. When sitting at a supercharger with a cold-ish battery the charge rate will start slow and go even slower which I think shows the battery is getting colder and colder. The SOC was < 50% when I noticed this. Meanwhile my S would start slow but speed up as the battery heated. Not sure how Tesla is gonna fix this if they didn’t put an auxiliary heater into the car since their surplus drivetrain energy doesn’t seem to be enough.

Also never seen the battery preheating symbol even in last years cold winter.
 
I supercharged in the "cold" 35 degrees today just to experiment. I drove about 28 miles to get there and arrived with about 44%. Supercharging started at 40kW and decreased to 30kW before I gave up.

It wasn't that cold and the charge rate was horrible!
 
I noticed that the other day. I'd been driving for 45 minutes plus preheated and the supercharger was slow to charge. I'm getting overly annoyed at the thought of winter coming and not being able to charge quickly because we're probably missing a key component for cold climate.
 
So we know the Model 3 uses the motor/inverter as a heater for the battery. It's very smart to do that, saves extra parts and simplifies the car.

The Lithium batteries in the Model 3 still have the same behavior and requirements regarding temperature. A Lithium battery cannot be charged when it is below 0 Celsius. That's a hard fact. So if you plug in any Tesla and the battery (please note I say battery, not ambient) temperature is below 0 Celsius, the car will halt charging, heat the battery until it goes over 0 C and then start charging. Also, the transition is not on/off. The charge rate depends on the battery temperature. at 0 C or lower, the charge rate is zero. At 25 Celsius the charge rate is full (up to 120 kW). In between the charge rate is reduced analog to the battery temperature.

Tesla knows what they are doing with the battery. Based on my own and other people's observation, Tesla uses active heating for the battery when the battery temperature is below aprox 8 Celsius. If the car is turned on (you are in it, or you start the climate control via the app, or it's charging) the car will heat the battery actively. If the car is parked and off, it will not heat the battery even if it falls below 8 Celsius and even if it is plugged in. Now while this info comes from the Model S/X I assume it works the same for the Model 3 because in the end it uses the same battery type which requires the same temperature management. The only difference is the method the heat is produced. Tesla does just fine with the temperature management. There is no need or advantage to let the owner set the heater by hand.

Charging the car will always also warm up the battery. Charging always has some heat losses inside the battery that will warm it up. If you want to 'manually' warm up the battery, time charging it so it finishes when you want the battery to be warm.
 
So we know the Model 3 uses the motor/inverter as a heater for the battery. It's very smart to do that, saves extra parts and simplifies the car.

Charging the car will always also warm up the battery. Charging always has some heat losses inside the battery that will warm it up. If you want to 'manually' warm up the battery, time charging it so it finishes when you want the battery to be warm.

We have no evidence that the motor inverter heat is actually enough. Why is my battery getting colder as it’s supercharging? Why does it take an hour of highway driving for the battery to heat up? In my S the battery would be heated in 20-25 minutes.
 
Should I drive a bit to warm up and then turn on air heating to save power, or is cabin heating so low it is not significant?

Cabin heating is significant. The best practice is (if possible) to start the cabin heater when the car is still plugged in. This way the power comes from the grid, not from the battery.

No it does not help to first drive a bit and then turn on the heater. The Model 3 is so efficient that there is very little heat losses that could be used. It's not like an ICE car that produces copious amount of waste heat as soon as the engine is running. In an EV the heat losses are not anywhere near enough to warm up the cabin.
 
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So we know the Model 3 uses the motor/inverter as a heater for the battery. It's very smart to do that, saves extra parts and simplifies the car.

The Lithium batteries in the Model 3 still have the same behavior and requirements regarding temperature. A Lithium battery cannot be charged when it is below 0 Celsius. That's a hard fact. So if you plug in any Tesla and the battery (please note I say battery, not ambient) temperature is below 0 Celsius, the car will halt charging, heat the battery until it goes over 0 C and then start charging. Also, the transition is not on/off. The charge rate depends on the battery temperature. at 0 C or lower, the charge rate is zero. At 25 Celsius the charge rate is full (up to 120 kW). In between the charge rate is reduced analog to the battery temperature.

Tesla knows what they are doing with the battery. Based on my own and other people's observation, Tesla uses active heating for the battery when the battery temperature is below aprox 8 Celsius. If the car is turned on (you are in it, or you start the climate control via the app, or it's charging) the car will heat the battery actively. If the car is parked and off, it will not heat the battery even if it falls below 8 Celsius and even if it is plugged in. Now while this info comes from the Model S/X I assume it works the same for the Model 3 because in the end it uses the same battery type which requires the same temperature management. The only difference is the method the heat is produced. Tesla does just fine with the temperature management. There is no need or advantage to let the owner set the heater by hand.

Charging the car will always also warm up the battery. Charging always has some heat losses inside the battery that will warm it up. If you want to 'manually' warm up the battery, time charging it so it finishes when you want the battery to be warm.
From batteryuniversity about charging below freezing:'Charging is indeed possible with most lithium-ion cells but only at very low currents. According to research papers, the allowable charge rate at –30°C (–22°F) is 0.02C. At this low current, the charge time would stretch to over 50 hours, a time that is deemed impractical. There are, however, specialty Li-ions that can charge down to –10°C (14°F) at a reduced rate.'

I can confirm that the Nissan Leaf allows some regen with battery being below 0C. It charges slow though. Kia Soul appears to do the same.

Tesla can allow charge/regen at sub zero temps if they want to, but there might be chemistry-based restrictions or they just want to be very careful. It could also have something to do with the batterycoolant they use.
 
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We have no evidence that the motor inverter heat is actually enough. Why is my battery getting colder as it’s supercharging? Why does it take an hour of highway driving for the battery to heat up? In my S the battery would be heated in 20-25 minutes.

And how do you know the battery is getting colder as it's supercharging?

Model S has a dedicated heater for the battery doesn't it. The Model 3 does not have that.