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Tesla scan on 120V charging in cold weather

Schulmann

Member
Nov 27, 2020
25
29
Toronto
I am driving a 2020 SR+, using Teslafi for logging. I drove 10000mi in 4 months. Mainly charging on Level 2 at home.

I just did my first 730mi trip to a remote location in cold weather around 30F. First day I had an average of 320 wh/mi, second day 300wh/mi, third day I did 285wh/mi and I also improved my charging rate and battery temperature for the departure.

During the night I had access to a 120V plug that I neglected the first day (waiting 2h before plugging in my Tesla).
One of the challenges was to get 98% battery charge for the morning around 9AM while keeping the battery in a warm state (keep charging until 8h59 ...). The night temperature was around 24F

Did anybody do a Tesla scan on a 120v Charge in cold weather ?
I would like to know how the Tesla keeps the battery warm during 120V charging and what happens when charging stop.
When i arrived to the nearest supercharge on saturday morning my battery was too cold :( little error that I fixed on Sunday.

There are many great videos on Supercharging in cold weather but none on 120V.
 

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theothertom

Member
May 9, 2020
300
182
South Carolina
Bjorn Nyland has a video on winter charging but I think he was using 240V charger. I don't have a link, sorry. It'll give you an idea of how much power is used to heat the battery.
 

GtiMart

Member
Nov 13, 2019
847
684
Quebec City, Canada
120V * 12A is 1.44kW... If the car decides the battery is too cold, it will use all that power for heating. It's less than the 6-7kW that it likes to use normally (or 3.5kW for single motor). If it's cold enough outside you might never reach the right battery temp. Said another way, your can might not gain any range (or very little) during the night.

If you do get range and reach your set point, it will stop charging and heating.

To arrive at the supercharger with a warm battery, either preheat the cabin before leaving or navigate to the sc, way in advance, especially if you have a single motor.
 

BabyYeggie

Member
Jul 22, 2019
30
30
YEG
I am driving a 2020 SR+, using Teslafi for logging. I drove 10000mi in 4 months. Mainly charging on Level 2 at home.

I just did my first 730mi trip to a remote location in cold weather around 30F. First day I had an average of 320 wh/mi, second day 300wh/mi, third day I did 285wh/mi and I also improved my charging rate and battery temperature for the departure.

During the night I had access to a 120V plug that I neglected the first day (waiting 2h before plugging in my Tesla).
One of the challenges was to get 98% battery charge for the morning around 9AM while keeping the battery in a warm state (keep charging until 8h59 ...). The night temperature was around 24F

Did anybody do a Tesla scan on a 120v Charge in cold weather ?
I would like to know how the Tesla keeps the battery warm during 120V charging and what happens when charging stop.
When i arrived to the nearest supercharge on saturday morning my battery was too cold :( little error that I fixed on Sunday.

There are many great videos on Supercharging in cold weather but none on 120V.

What's your definition of cold? 30F is warm. At that temperature, there's no effect on charging. You should still get around 5mph/8kmph.

It's only when you get to really low temperatures, like below -20C that it makes a difference. The rapid decrease in range is from pre-heating.

charging-32.JPG
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,247
7,290
Boise, ID
The night temperature was around 24F
What's your definition of cold? 30F is warm. At that temperature, there's no effect on charging. You should still get around 5mph/8kmph.

It's only when you get to really low temperatures, like below -20C that it makes a difference.
Yes, this, although it might be a little less than the usual 5 mph.
120V * 12A is 1.44kW... If the car decides the battery is too cold, it will use all that power for heating. It's less than the 6-7kW that it likes to use normally (or 3.5kW for single motor). If it's cold enough outside you might never reach the right battery temp. Said another way, your can might not gain any range (or very little) during the night.
Yeah, it will probably need to do some heating, but it can scale the power level or cycle it on and off. So maybe it won't charge much for the first half hour or hour, but with 24 degrees, it should get to a point where it can charge pretty normally for most of the night.
 

GtiMart

Member
Nov 13, 2019
847
684
Quebec City, Canada
Let us know, I'm curious to learn how it will behave at around 24F. I've only heard bad stories in cold weather (which for me is well below 0C / 32F BabyYeggie ) where the car would essentially not gain any range. I haven't experienced it myself but I did see most of the 6-7kW of a level2 charger being used to heat my battery for a good while before range started going up in one charging session I remember last winter.
 

BabyYeggie

Member
Jul 22, 2019
30
30
YEG
24F still won't affect charging. A quick search for the weather in Quebec City shows a normal low of -17C in January, so here's the closest charge I have. It shouldn't be significantly different.

Notice that the first 15 minutes or so, the slope of the range increase is nearly flat. Then, there's a big jump in range after the battery warms up enough. This should be representative of parking your car outside since I normally charge in the afternoons after the car has been parked for around 4 hours, enough time to be cold soaked.

Capture.JPG
 
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Gasaraki

Active Member
Oct 21, 2019
1,655
1,063
Syracuse, NY
I am driving a 2020 SR+, using Teslafi for logging. I drove 10000mi in 4 months. Mainly charging on Level 2 at home.

I just did my first 730mi trip to a remote location in cold weather around 30F. First day I had an average of 320 wh/mi, second day 300wh/mi, third day I did 285wh/mi and I also improved my charging rate and battery temperature for the departure.

During the night I had access to a 120V plug that I neglected the first day (waiting 2h before plugging in my Tesla).
One of the challenges was to get 98% battery charge for the morning around 9AM while keeping the battery in a warm state (keep charging until 8h59 ...). The night temperature was around 24F

Did anybody do a Tesla scan on a 120v Charge in cold weather ?
I would like to know how the Tesla keeps the battery warm during 120V charging and what happens when charging stop.
When i arrived to the nearest supercharge on saturday morning my battery was too cold :( little error that I fixed on Sunday.

There are many great videos on Supercharging in cold weather but none on 120V.

The 120V charging doesn't really provide enough heat and provide a good charge to the batteries. You can charge normally during the night and then about an hour before you leave, preheat the car via the app. That will preheat the batteries also. However when you preheat, the batteries won't really be charging.
 

Schulmann

Member
Nov 27, 2020
25
29
Toronto
Finally bought Scan my Tesla and figured out thoose magical numbers:
below -7C BMS will drain current to keep the battery warm.
Stator uses 3kw to heat battery so on 120v this is a killer.
Batt Target temp for 120V charging 3C and 7C for 240V
Batt Target temp for road is 12C
Batt Target for full speed supercharging is around 45C but pre conditionning only heats to 21c !
 
Last edited:

camalaio

Active Member
May 28, 2019
1,483
2,093
Vernon, BC, Canada
Finally bought Scan my Tesla and figured out thoose magical numbers:
below -7C BMS will drain current to keep the battery warm.
Stator uses 3kw to heat battery so on 120v this is a killer.
Batt Target temp for 120V charging 3C and 7C for 240V
Batt Target temp for road is 12C
Batt Target for full speed supercharging is around 45C but pre conditionning only heats to 21c !

Have to be careful interpreting data from ScanMyTesla - the names for the fields are from the developer, not from Tesla, and may be slightly misleading unless you've really dug into it. For example, that target temp for Supercharging was likely the battery coolant inlet temperature target, which is not the same thing as "get the battery to 45C" since a significant temperature difference is required to actually heat the battery quickly. You don't actually see the battery target value with this app.

Rough points:
  1. Each motor uses 3-4kW max for battery heating. If you have a RWD model, the heating is slower as a result.
  2. Unlike other operations, it will try to keep "net zero" power while heating. Any excess will go to charging. If you only have 1400W available (e.g. 120V charging), only about 1kW will be used to heat the battery.
  3. The target temps are incredibly misleading if you take them at face value, as more factors are involved and where they apply changes.
The more accurate description of the heating behaviour is something like:
  • On AC charging, keep the battery above 10C (50F). Heat with available power when needed, up to 3-4kW per motor.
  • For driving, keep the battery above 0C (32F). Heat with maximum power when needed, 3-4kW per motor.
  • For Supercharging/preconditioning, it varies by arrival SoC and can be happy with just 25C upon arrival if you're very low on charge. Generally it'll approach 60C, especially later in the charge.

Anecdotally, around -10C (14F), when parked outside, only 40% or so of the otherwise expected power is used to actually charge the battery (worse if windy). The rest is used in cycles to heat the battery, then it charges until it's too cold again. At -20C (-4F), many people have reported that charging outside off a standard 120V just doesn't work (it needs to maintain a 30C (!!) temperature difference, and is not really insulated from the cold). However, it is helping the battery not discharge (at these temps, it would be trying to heat it occasionally while parked).

Source: Currently charging off of 120V block heater outlet in a cold-ish mountain town (-12C or so overnight), have looked into CAN bus data (and SMT) for about a year specifically trying to understand temperature management.

A lot of anecdotal data posted here has problems. For example, in a thread like this, it was claimed that it doesn't heat the battery in the cold for charging because they got the full 7km/hr when plugged into a 120V outlet in -10C temps. The full story there was that the car was plugged in after returning from work - the car actively heated above 0C for driving purposes, and then they drove for a while which also heated the battery (waste heat). So it was already warm enough when they started charging! What I'm trying to say with this is that driving habits can have a significant influence on one's experience, as well as when the data is collected and for how long. These factors impact both what you may think the car does, as well as what the actual impact is in terms of power usage. In my case for example, the car sits most of the time (gets very cold) and maybe travels 5km total per day, yet uses 40km of range. Charging for 16 hours nets me about 50km on a good day, barely keeping up.
 

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