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interesting Scan My Tesla charging results

rrolsbe

Member
Feb 18, 2017
231
129
Albuquerque
I charge my M3 RWD using a 240V 24A Nema 10-30. When the traction battery cell temps are below 54F and above 44F, it charges at 7 to 8 MPH instead of the normal 22 to 23 MPH. I have not charged with cell temps below 45F this year but from last year temps around 40F no miles were added initially while the traction battery was warming. As soon as the cell temp reaches 54F, the traction battery heating stops and the charge rate reaches 22 to 23 MPH. Since I was getting 8MPH and the remaining power was used for heating, I assumed no heating would be needed if I set the amperage setting to 5A; however, all of the power was sent to the stator for traction battery heating with a MPH charge level of 0. Logic told me that at 50F cell temps no battery heating would be required at the 5 Amp setting so I was surprised by the 0 MPH.
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
10,043
12,097
San Diego
Yeah. If it was just a step change at 54 degrees then you would expect that at 50 degrees 5A would be all heat.

Looks like 3.4kW AC is being allocated to heat, so 5A is not enough below 50.
 

rrolsbe

Member
Feb 18, 2017
231
129
Albuquerque
Guess I was not very clear in my first original post. If the car can charge at 8MPH at a 50F cell temp at 24A, why does it not charge at around 3 to 4MPH at 5A instead of only heating the battery.? The battery appears to be able to take a charge of at least 7MPH at 50F at the beginning of charging session of 24A. If I was visiting a friend or relative and had to plug my UMC into a 120V outlet and lower the amperage to 10A, I would prefer the car charged at 3-4 MPH at 50F cell temp instead of only heating the cells but I am not overly worried about it. It would be interesting to see a chart of the cell temps versus MPH at given KW power level. I believe the cell temps need to be at 90F or greater to accept a charge of 150KW at a supercharger and the cells will definitely not accept ANY charge at 32F.
 
Last edited:

ewoodrick

Well-Known Member
Apr 13, 2018
5,285
3,732
Buford, GA
And again, not much need to worry about it. It's not as if there is much you can do.

It sounds as if the moral of the story is:
If the battery is cold, it won't charge as fast. i.e. keep it in a garage whenever possible.
 

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