How much energy to preheat battery and car from 20F?

[cstork]

Can someone answer these questions:
1) If the car and battery are at 20F (-7C), how many KWh are used to bring the car and battery up to 70F (21C) ? I assume this doesn't make a difference whether driving or pre-heating.
2) How long does it take for the battery to heat up from 20F to 70F when doing preheat not plugged in?
Thank you.

 

[WesB]

I did a test from -14C to 10C, temp set to 21C and both front heated seats on. (It didn't reach 21C because I got in the car and left before it had the chance). Took 3-4 minutes and consumed 4 km of range (about 0.5 kWh).

 

[PACEMD]

How are you going to know what temperature the battery is?

 

[rrolsbe]

If I had to guess, it would take at least 10KWH to heat the traction battery from 20F to 70F.

 

[1.21GW]

Battery will take a very long time, it’s thermal mass is huge. Plus, if it is 20 degrees, your battery temp won’t likely get to 70 degrees unless you are driving it hard.

also... are you using some app to determine battery temp?

 

[Garlan Garner]

I wonder why dual motor model 3's pre-heat their batteries for supercharging by creating heat from the front motor?

I also wonder how single motor model3's pre-heat their battery?

One of he reasons I ask about the dual motor preheating is because the rear motor is ALWAYS warmer than the front motor on expressways. Tesla could be a little more efficient and use the rear motor's heat until the front motor's heat catches up. Hmmmm

 

[GZDongles]

I wonder why dual motor model 3's pre-heat their batteries for supercharging by creating heat from the front motor?

I also wonder how single motor model3's pre-heat their battery?

One of he reasons I ask about the dual motor preheating is because the rear motor is ALWAYS warmer than the front motor on expressways. Tesla could be a little more efficient and use the rear motor's heat until the front motor's heat catches up. Hmmmm

Hey Garlan, I'm by no means an expert on this, but Bjorn Nyland has some excellent videos on YouTube that go over the preheating logic. Basically the front motor is rarely used at steady highway speeds so it can have a dedicated 3.5 kW for heating the battery.

To answer the initial question, in a dual motor, 3.5 kW per motor (7kW) can be used to preheat the battery, and up to 9kW can be used to precondition the cabin (~7kW for the PTC heat and 2 kW for air conditioning to dehumidify). The cabin heats up relatively quickly, and it's probably more like 1-2 kW steady-state to hold the cabin at 70F when the outside temp is 20F. The battery could take close to an hour to heat up to 70F from 20F.

So, total, you would be looking at 7 kWh for that hour to heat the battery + ~3kWh to keep the cabin warm for an hour. So it uses quite a bit of energy to pre heat the battery! It's probably not worth fully preheating the battery if you aren't plugged in. The energy used to preheat will be more than you could gain from increased regen and unlocking the full battery capacity. If you are preheating when plugged in and going on a long trip, probably worth it to preheat as much as possible to maximize range!

 

[Garlan Garner]

Hey Garlan, I'm by no means an expert on this, but Bjorn Nyland has some excellent videos on YouTube that go over the preheating logic. Basically the front motor is rarely used at steady highway speeds so it can have a dedicated 3.5 kW for heating the battery.

To answer the initial question, in a dual motor, 3.5 kW per motor (7kW) can be used to preheat the battery, and up to 9kW can be used to precondition the cabin (~7kW for the PTC heat and 2 kW for air conditioning to dehumidify). The cabin heats up relatively quickly, and it's probably more like 1-2 kW steady-state to hold the cabin at 70F when the outside temp is 20F. The battery could take close to an hour to heat up to 70F from 20F.

So, total, you would be looking at 7 kWh for that hour to heat the battery + ~3kWh to keep the cabin warm for an hour. So it uses quite a bit of energy to pre heat the battery! It's probably not worth fully preheating the battery if you aren't plugged in. The energy used to preheat will be more than you could gain from increased regen and unlocking the full battery capacity. If you are preheating when plugged in and going on a long trip, probably worth it to preheat as much as possible to maximize range!

I didn't know I could select to pre-heat or not. Thanks for the information. I'll look him up.

 

[Geir]

Hi!
I think there is noe moment to add:
Preheating of the battery is important to battery health. The battery will last longer if you preheat in cold conditions.

 

[GZDongles]

Hi!
I think there is noe moment to add:
Preheating of the battery is important to battery health. The battery will last longer if you preheat in cold conditions.

I'd imagine there's a balance to be had though depending on temperature and usage. For short drives, preheating for longer than a few minutes could literally double or triple your energy consumption (for instance for drives of a few miles to the store). This is all adding to the battery cycle count. So at some point, adding more cycles to the battery will be worse than operating a cold battery.

 

[pt19713]

Can someone answer these questions:
1) If the car and battery are at 20F (-7C), how many KWh are used to bring the car and battery up to 70F (21C) ? I assume this doesn't make a difference whether driving or pre-heating.
2) How long does it take for the battery to heat up from 20F to 70F when doing preheat not plugged in?
Thank you.

Year, make, model? It'll vary depending on 2018-2020, 2021+

 

[pt19713]

Hey Garlan, I'm by no means an expert on this, but Bjorn Nyland has some excellent videos on YouTube that go over the preheating logic. Basically the front motor is rarely used at steady highway speeds so it can have a dedicated 3.5 kW for heating the battery.

FYI, it's 3.5 kW per motor while parked. While driving, if you have the Tesla supercharger as the NAV location, the front induction motor will drop from 3.5 kW to 2.0 kW. At 2.0 kW, it's not generating as much heat. While parked, my Model Y can get up to 210F on the front Stator motor but while driving, I'm only seeing it max out around 125F in temps of 32-33F.

 

[GZDongles]

FYI, it's 3.5 kW per motor while parked. While driving, if you have the Tesla supercharger as the NAV location, the front induction motor will drop from 3.5 kW to 2.0 kW. At 2.0 kW, it's not generating as much heat. While parked, my Model Y can get up to 210F on the front Stator motor but while driving, I'm only seeing it max out around 125F in temps of 32-33F.

Thanks, that's great info! Do you notice the rear stator heating up above the baseline driving level as well?

 

[camalaio]

I'll be able to get you an answer this week probably! This'll be an expensive experiment.

For those temperatures, the cabin is comfortable enough in 5 minutes, toasty in 10. But for the battery, my early guess is it would take over an hour, but there are variables. I'll expand.

First, AWD vs RWD matters because the motors are what's being used to heat the battery. They do this best while not driving though. When driving, the rear motor is mostly preoccupied with moving the car rather than generating heat. If you don't have a front motor, heating will be a lot slower while in drive.

While parked, RWD models will take over twice as long to heat up the battery. This is because they only have half the heating power, but that longer time spent heating to a certain point means they've also lost more heat to the outside world.

I've never preheated the car long enough for it to reach 20C on the battery. This is partly because it would take well over an hour in those temps, but primarily because it is a colossal waste of energy. If I assume best case scenario, 8kW average (AWD) for an hour, that's 8kWh to warm the battery.

I say that's best case, because I've preheated it for half an hour on a few occasions and the temperature did not go up all that much, certainly less than 10C. To make a difference of 28C (-7C to 21C) takes a lot of energy for that 1000lb battery, and it also takes energy to just maintain that temperature since it's cold outside. In reality, the moment you start driving, that temperature will start dropping. I'd guess it would drop to around 15C steady state, assuming it was -7C outside.

---

The car will use the same amount of power/energy when preheating the cabin and battery, whether you are plugged in or not. In the (likely) case that heating power needs exceed what is available from the plugged in source, any additional needed power is taken from the battery.

FYI, it's 3.5 kW per motor while parked. While driving, if you have the Tesla supercharger as the NAV location, the front induction motor will drop from 3.5 kW to 2.0 kW. At 2.0 kW, it's not generating as much heat. While parked, my Model Y can get up to 210F on the front Stator motor but while driving, I'm only seeing it max out around 125F in temps of 32-33F.

This isn't necessarily inaccurate, but there are multiple behaviours for heat generation while in drive. This is only one of them.

It seems to change behaviours based on distance to Supercharger, SoC (which implies what temperature is needed), and probably some other factors I don't know.

 

[pt19713]

Thanks, that's great info! Do you notice the rear stator heating up above the baseline driving level as well?

This one is difficult to test because the car is primarily RWD, so there's heat being generated from normal driving. Generally I find the front motors, in 35-40F temps, hovering around 80-95F and the rear motors hover around 90-120F. Note, these are on my Y so there may be some variation in the Model 3.

 

[pt19713]

This isn't necessarily inaccurate, but there are multiple behaviours for heat generation while in drive. This is only one of them.

It seems to change behaviours based on distance to Supercharger, SoC (which implies what temperature is needed), and probably some other factors I don't know.

I've been logging data on preconditioning since November, so I'm going off my own data. Obviously if people have their own, they can post and people can make their own decisions. My various graphs and data has been posted in the Model Y section (Battery & Charging).

edit: more info. My 2.0 kW from the front motor is based upon two scenarios. I've seen it when navigating to a supercharger where the battery pack was only 51F, starting SoC 14% and expected arrival at the supercharger at 9%. It would've had plenty of juice to power 3.5 kW of heat. The other scenario I've seen it is in slightly warmer temps where I used the function to warm up the batteries to test out 0-60 and quarter mile times. Ambient temps were 60F, battery packs were 70F but I wanted to get them to 85F. SoC 89% and the front motors were still only pulling 2.0 kW. If there's a scenario where they will pull the normal 3.5 kW, I haven't found it.

 

[camalaio]

I've been logging data on preconditioning since November, so I'm going off my own data. Obviously if people have their own, they can post and people can make their own decisions. My various graphs and data has been posted in the Model Y section (Battery & Charging).

edit: more info. My 2.0 kW from the front motor is based upon two scenarios. I've seen it when navigating to a supercharger where the battery pack was only 51F, starting SoC 14% and expected arrival at the supercharger at 9%. It would've had plenty of juice to power 3.5 kW of heat. The other scenario I've seen it is in slightly warmer temps where I used the function to warm up the batteries to test out 0-60 and quarter mile times. Ambient temps were 60F, battery packs were 70F but I wanted to get them to 85F. SoC 89% and the front motors were still only pulling 2.0 kW. If there's a scenario where they will pull the normal 3.5 kW, I haven't found it.

Sorry, my bad for not explaining more. I'm not saying there's a driving scenario in which it'll pull 3.5kW, but there's plenty of ways it can use less than 2kW. That will also depend on driving conditions, especially city driving vs. highway. I'm just saying a flat 2kW burn is only one of many options it has, and what it does can vary during the preconditioning duration.

That said the Model Y could be behaving differently with the heat pump. I haven't seen anything indicating otherwise (it's also not a great use-case for the heat pump), but I haven't looked very deep into it either.

 

[pt19713]

Sorry, my bad for not explaining more. I'm not saying there's a driving scenario in which it'll pull 3.5kW, but there's plenty of ways it can use less than 2kW. That will also depend on driving conditions, especially city driving vs. highway. I'm just saying a flat 2kW burn is only one of many options it has, and what it does can vary during the preconditioning duration.

That said the Model Y could be behaving differently with the heat pump. I haven't seen anything indicating otherwise (it's also not a great use-case for the heat pump), but I haven't looked very deep into it either.

Yeah, that's why I asked yr/make/model since there may be differences. Original poster hasn't responded, though.

 

[Gasaraki]

I did a test from -14C to 10C, temp set to 21C and both front heated seats on. (It didn't reach 21C because I got in the car and left before it had the chance). Took 3-4 minutes and consumed 4 km of range (about 0.5 kWh).

He's asking about the battery temp, not the interior temp. The interior temp warms up quickly 4 mins or so. The battery, not so much.

If you use the car preheat feature, the car usually stop preheating the battery after about half hour. It doesn't mean that the battery temperature is at 20C. It just warms it enough to not be super cold. When I do it, I've noticed it drop 4% charge or so?

 

[Gasaraki]

I wonder why dual motor model 3's pre-heat their batteries for supercharging by creating heat from the front motor?

I also wonder how single motor model3's pre-heat their battery?

One of he reasons I ask about the dual motor preheating is because the rear motor is ALWAYS warmer than the front motor on expressways. Tesla could be a little more efficient and use the rear motor's heat until the front motor's heat catches up. Hmmmm

The LR-AWD uses the motor to preheat the battery because the front motor is the less efficient of the two. It naturally generates more wasted heat when running.

On expressways the rear motor is always warmer than the front because the Model 3 is a rear wheel drive car. On the motorway, the front motor is not used unless needed for traction or acceleration. A unused motor is cooler than a used one.