Battery conditioning power draw in cold weather

[NoSmoke99]

Hello all, first post. Was wondering if anyone has measured power consumption when plugged in during periods of cold weather. As I understand it, the BMS will draw power to keep the battery above a certain temperature, that power either coming from the charger or from the battery itself.

If it's say, -20C (-4F) or so in a non-insulated, detached garage, how much power would be consumed only for maintaining battery temperature? I have a feeling the amount could be significant if the vehicle is left undriven and plugged in for several days or so(?).

Also, what happens if the vehicle is simply left unplugged? Would battery degradation occur (assuming it is not left to drain completely)?

 

[GtiMart]

I don't believe it's ever been proven that the car would heat the battery in that situation. The car will wake up from time to time to charge the 12V but that should be all. I don't think being plugged makes a difference here.
The battery should degrade less in cold weather. The manual does state not to leave the battery at -30C or lower for more than 24h at a time however so it might be detrimental in that case.

 

[islandbayy]

It's not going to heat the battery while parked until the temperature reaches about -30*F/C (Since both are nearly the same temperature at that point). Once driving or pre-conditioning via the app though.
Also, being in a closed garage, even if unheated, helps amazingly! You are taking wind chill out of the equation. Charging itself warms the battery.

 

[NoSmoke99]

I don't believe it's ever been proven that the car would heat the battery in that situation. The car will wake up from time to time to charge the 12V but that should be all. I don't think being plugged makes a difference here.
The battery should degrade less in cold weather. The manual does state not to leave the battery at -30C or lower for more than 24h at a time however so it might be detrimental in that case.

OK, thanks for that. If the car/battery had cooled to ambient temperature though (say -20 or -30) and it was then plugged in I suppose the charge current would first be directed to heating the battery to at least the minimum charging temperature before battery charging commenced (IIRC lithium batteries have to be at or above 0C before they can be charged)? I wonder then how long that would take assuming a level 2 charger? It would be a bit of a bummer if one had to wait a day or whatever for the battery to warm up and be recharged!

I dunno, maybe I'm overthinking this - it doesn't seem to be a topic of great concern from what I have read on this and other forums.

 

[NoSmoke99]

It's not going to heat the battery while parked until the temperature reaches about -30*F/C (Since both are nearly the same temperature at that point). Once driving or pre-conditioning via the app though.
Also, being in a closed garage, even if unheated, helps amazingly! You are taking wind chill out of the equation. Charging itself warms the battery.

Yes, a closed garage will help a lot because, as you say, no wind chill and, the concrete floor holds a lot of residual heat that will help to reduce temperature drop at least for a day or two. Any sun shining on the garage would also help.

 

[GtiMart]

Yes, at the moment when the car needs to charge, the battery will need to be heated before it can accept a charge. It needs to be somewhere over freezing before it can start charging. What I'm saying is that the car doesn't just "keep the battery warm" all the time.

You are right that it takes a significant amount of energy to heat a big battery pack. As long as the energy source provides enough power, the car will eventually start charging.

 

[islandbayy]

OK, thanks for that. If the car/battery had cooled to ambient temperature though (say -20 or -30) and it was then plugged in I suppose the charge current would first be directed to heating the battery to at least the minimum charging temperature before battery charging commenced (IIRC lithium batteries have to be at or above 0C before they can be charged)? I wonder then how long that would take assuming a level 2 charger? It would be a bit of a bummer if one had to wait a day or whatever for the battery to warm up and be recharged!

I dunno, maybe I'm overthinking this - it doesn't seem to be a topic of great concern from what I have read on this and other forums.

Correct, charge current is directed to heating first. How long it takes, depends on what year vehicle you have. The S & X with the battery heater, which is 6kW, even starting with -30 you will see at least minimal charging in about 15-20 minutes if cold soaked at -30. It WILL be SLOW, but it will start. Then it compounds. Charging in and of itself generates heat. So charging + pack heater +faster and faster and faster charge rate.
3 & Y are a different story. Early 3's had no pack heater, and only had resistive cabin heat, so no heat pump. In that case, the car puts the motor in a "stall". Or in other words, generates a magnetic field in the motor that does not propel the vehicle. This generates waste heat. It works like crap, but better than nothing since Tesla cheeped out on not having a pack heater.

For heat pump 3 & Y, they use the heat pump to draw ambient heat from the air and funnel it into the battery. It is much slower than the resistive heater, ESPECIALLY at those nasty cold temps, however, works much better than the 10kW stall they were using, and the heat pump still uses astronomically less power than battery heater or stalling the motor.

 

[islandbayy]

In your temps, The lowest powered wall charger i'd recommend would be 10kW, or in other words, try and max out the car's charging abilities at home.

 

[XPsionic]

If it's say, -20C (-4F) or so in a non-insulated, detached garage, how much power would be consumed only for maintaining battery temperature? I have a feeling the amount could be significant if the vehicle is left undriven and plugged in for several days or so(?).

If I were to venture a guess based on what other owners have said about how they get 3-4kw power from a 7kw Level 2 charger when it's like -35c outside, battery conditioning/heating takes somewhere around 2-3kw. Another data point is people who use a normal 120v outlet being unable to charge at -20c or lower. A 120v normal outlet is like 1.6kw max.

 

[gsmith123]

In your temps, The lowest powered wall charger i'd recommend would be 10kW, or in other words, try and max out the car's charging abilities at home.

I've used 5kw charging (outdoors) in cold temperatures (down to -10f or so). Sure, when the pack is really cold soaked it takes some time to warm it up. But it's not that much time. Maybe an hour or so of extra charging time?

An hour doesn't meaningfully impact overall charge times if you're charging overnight or while parked at work. A 20-80% charge might go from 7 hours to 8 hours (roughly speaking).

And if you can charge immediately after driving when the battery is warm anyway.

I personally don't see much need for faster charging for 3 and Y owners. CT and other larger batteries, sure.

(I have a pre-heatpump Model 3 AWD, so it can dump about 5kw of waste heat from the motors into the battery for heating)

 

[Benito1283]

I wonder then how long that would take assuming a level 2 charger? It would be a bit of a bummer if one had to wait a day or whatever for the battery to warm up and be recharged!

Definitely not a day. Maybe 30 minutes until the battery was warmed enough to where could charge at fully speed.

 

[DuncanM]

Hello all, first post. Was wondering if anyone has measured power consumption when plugged in during periods of cold weather. As I understand it, the BMS will draw power to keep the battery above a certain temperature, that power either coming from the charger or from the battery itself.

If it's say, -20C (-4F) or so in a non-insulated, detached garage, how much power would be consumed only for maintaining battery temperature? I have a feeling the amount could be significant if the vehicle is left undriven and plugged in for several days or so(?).

Also, what happens if the vehicle is simply left unplugged? Would battery degradation occur (assuming it is not left to drain completely)?

This short video is highly relevant to you and is very informative:

 

[DuncanM]

Here's another video of a road trip in in -27c weather:

 

[NoSmoke99]

This short video is highly relevant to you and is very informative:

Hey thanks, excellent info, even though it appears to seriously contradict Tesla's documentation. I'm beginning to understand why there is so much contradictory information on the topic of cold weather battery maintenance, on other manufacturer forums as well as this.

And, the guy lives in Rocky View County (Alberta) as do I.

Methinks I will look up his other YouTubes as well.

 

[XPsionic]

Hey thanks, excellent info, even though it appears to seriously contradict Tesla's documentation. I'm beginning to understand why there is so much contradictory information on the topic of cold weather battery maintenance, on other manufacturer forums as well as this.

And, the guy lives in Rocky View County (Alberta) as do I.

Methinks I will look up his other YouTubes as well.

Windchill does matter because airflow speeds up heat loss from the battery pack. The video was shot inside an uninsulated garage, and even though cold, it was still a good 10c warmer than outside. All of that heat's coming from charging the car.

Even in the video's comments you'll see mentions of 120v not being able to charge at roughly -25c or so.

 

[NoSmoke99]

If I were to venture a guess based on what other owners have said about how they get 3-4kw power from a 7kw Level 2 charger when it's like -35c outside, battery conditioning/heating takes somewhere around 2-3kw. Another data point is people who use a normal 120v outlet being unable to charge at -20c or lower. A 120v normal outlet is like 1.6kw max.

Yeah, 2 to 3 KW is the range I'm seeing from other sources but, that doesn't give the cumulative energy consumption as the heater on/off cycle time has to be considered. If it's v cold for example and the heater is on 1/2 the time, the daily consumption would be 36 KWh per day (assuming a 3 KW draw)! That BTW would be about 3 times on average what my currently non-EV household consumes.

 

[NoSmoke99]

Windchill does matter because airflow speeds up heat loss from the battery pack. The video was shot inside an uninsulated garage, and even though cold, it was still a good 10c warmer than outside. All of that heat's coming from charging the car.

Even in the video's comments you'll see mentions of 120v not being able to charge at roughly -25c or so.

Yes, it looks like -25 would indeed be a problem for 120V charging and also a significant power consumption issue for 240V charging.

 

[DuncanM]

Yes, it looks like -25 would indeed be a problem for 120V charging and also a significant power consumption issue for 240V charging.

A simple upgrade is to convert a 120v NEMA 5-15 outlet to a NEMA 5-20 (requires a 20amp breaker and 12-2 wire and the requisite plug adapter for the TMC ); this will allow charging at 16a/120v. In a garage this would help quite bit. Another low cost upgrade, if an outlet is on a dedicated breaker, would be to upgrade it to a NEMA 6-15 (14-2 wire) or 6-20 12-2 wire and a 15 or 20amp 240v breaker.

 

[Sti-g]

Perhaps another idea is to charge when you arrive home, while the battery is still warm.

 

[NoSmoke99]

This short video is highly relevant to you and is very informative:

Thank you for that - it is as described. The channel owner has also replied to my query in the comments and is ready to take some power consumption measurements for his new Mach E when it gets cold again (forecast is for warming up next week and +17C next Saturday however).