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Mysterious (temporary) drop in regenerative braking (what can cause this?)

Rothgarr

Member
Apr 15, 2019
838
690
United States
Howdy. On two occasions now (that I noticed), I had been driving my 2019 LR AWD Model 3 and the regen bar (which previously had no dots) will slowly creep to between 1/3 and 1/2 dots. Since I do one-pedal driving, I'll notice that the car doesn't slow down as quickly which makes me notice the dots. I think at least one time the "limited regenerative braking" message came up on the screen. Then, within five minutes, the dots slow completely disappear and go back to normal.

Normally I'd find this behavior normal, but the circumstances make it unusual:
  • The SOC was between 75% and 79% each time.
  • The outside temperature was at least 75 degrees each time
  • I had already been driving for at least 10 minutes each time

I'm aware of how regenerative braking can be limited if you are near 100% SOC or when it's cold (I've been through two cold CT winters). Has anyone else gotten this behavior under which should be optimal conditions for regenerative braking?

THanks!
 

GtiMart

Member
Nov 13, 2019
971
810
Quebec City, Canada
When the car is close to the limits where regen would be reduced, using the regen might make it reduce. I remember a couple of drives using ScanMyTesla where I could see the max regen reduce while I was going down a hill and regenning... Once I accelerated after the stop sign at the bottom of the hill, max regen slowly went back up.
So, using regen and putting back 60-85kW of power in the battery, the bms adjusts max regen continuously. 85kW is a lot of power for a high SOC. Clearly the BMS doesn't want you to do that for too long. You might see that more when going down bigger hills.
Said another way, max regen is a dynamic limit that gets continuously adjusted based on multiple factors, and how you use regen is one of those factors.
 

Rothgarr

Member
Apr 15, 2019
838
690
United States
When the car is close to the limits where regen would be reduced, using the regen might make it reduce. I remember a couple of drives using ScanMyTesla where I could see the max regen reduce while I was going down a hill and regenning... Once I accelerated after the stop sign at the bottom of the hill, max regen slowly went back up.
So, using regen and putting back 60-85kW of power in the battery, the bms adjusts max regen continuously. 85kW is a lot of power for a high SOC. Clearly the BMS doesn't want you to do that for too long. You might see that more when going down bigger hills.
Said another way, max regen is a dynamic limit that gets continuously adjusted based on multiple factors, and how you use regen is one of those factors.
That's interesting. The other weird thing was, I hadn't (and wasn't) going down a hill or anything either time it happened.
 

GtiMart

Member
Nov 13, 2019
971
810
Quebec City, Canada
Well... I talked about going down big hills because that makes a lot of regen, but I guess highway driving and then exiting, or stop/go traffic on the highway, might be similar. Any condition where you use significant regen for more than a second. Otherwise, not sure what it could be.
 

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