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Regen consistency?

jjgg

Member
May 21, 2021
226
287
Vancouver
Maybe I'm too new an owner of MY, but I found the Regen brake behaviour inconsistent. From similar distances and similar speed, if I completely let go the accelerator pedal, sometimes I can stop without issues but sometimes I had to step on the brake pedal.

Do you observe the same thing?
 

Fourdoor

Member
May 31, 2016
873
696
North East Arkansas
Maybe I'm too new an owner of MY, but I found the Regen brake behaviour inconsistent. From similar distances and similar speed, if I completely let go the accelerator pedal, sometimes I can stop without issues but sometimes I had to step on the brake pedal.

Do you observe the same thing?
Are you charging to 100% on a regular basis?

Keith
 

PDX-Y

Member
May 24, 2021
102
98
Portland, OR
Are you charging to 100% on a regular basis?
To clarify for those who didn't understand the implication of the question: when the battery is very near the top of the charge curve, it has no "space" to put more energy from the motor, so regenerative braking works poorly and you have to use the real brakes to stop. Once you have some buffer, there's plenty of room and things work normally.
 
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jjgg

Member
May 21, 2021
226
287
Vancouver
Are you charging to 100% on a regular basis?

Keith
No, I set charge limit to 80%.

A few times, at the same location near my home, I got the screen prompt that regenerative braking is reduced. I don't know why because the battery was at 80% at the time.

But for the situations I mentioned in my first post (about the inconsistency), there was no such prompt on the screen.
 

stopcrazypp

Well-Known Member
Dec 8, 2007
10,804
5,716
No, I set charge limit to 80%.

A few times, at the same location near my home, I got the screen prompt that regenerative braking is reduced. I don't know why because the battery was at 80% at the time.

But for the situations I mentioned in my first post (about the inconsistency), there was no such prompt on the screen.
Regen also varies on temperature and if you have a long downhill section where it is charging it at high rates for a while, it might also limit it. Given the pack is a large thermal mass, if you cold soak it overnight, it may take a while for the temp to recover. The car also scavenges heat from the battery, so usage of heating in the car may also affect this.

Note when the regen is limited, you can see a dotted line on the left of the power meter. This may show up before the warning message.
 
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jjgg

Member
May 21, 2021
226
287
Vancouver
Regen also varies on temperature and if you have a long downhill section where it is charging it at high rates for a while, it might also limit it. Given the pack is a large thermal mass, if you cold soak it overnight, it may take a while for the temp to recover. The car also scavenges heat from the battery, so usage of heating in the car may also affect this.

Note when the regen is limited, you can see a dotted line on the left of the power meter. This may show up before the warning message.
This sounds about the right reason. If I recall, I always get "regen reduced" warning after the first downhill section out of my home before the traffic light, the first ride in the morning, and I probably didn't plug in the car overnight in those occasions.
 
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jjgg

Member
May 21, 2021
226
287
Vancouver
This sounds about the right reason. If I recall, I always get "regen reduced" warning after the first downhill section out of my home before the traffic light, the first ride in the morning, and I probably didn't plug in the car overnight in those occasions.
OK, I tried a few things and I think I have a better understanding of it now.

First, the dotted lines on the energy bar is a really handy detail to tell me the regen status. I noticed not every time the car will give me text prompts about it, but the dots are there consistently with the reduced regen behaviour.

I tried to use scheduled precondition for my first morning drive. I think it improves things. At least I can see no dotted lines at the beginning and I don't get the reduction at the usual place. However, as I drive further along, the dots started to show up. I think what happened was that the precondition only warmed up the battery slightly (to save energy) to a level that's not as warmed up as driving continuously. I have 5 minutes of downhill so maybe half way through that, the preconditioned battery was still not warm enough to take more regen charges.
 

AlexHung

Member
Mar 13, 2021
303
284
Santa Cruz, CA
I have 5 minutes of downhill so maybe half way through that, the preconditioned battery was still not warm enough to take more regen charges.
I believe the opposite is happening. After a period of regen (through descending), the battery temperature is too high for max regen.
 

Fourdoor

Member
May 31, 2016
873
696
North East Arkansas
I believe the opposite is happening. After a period of regen (through descending), the battery temperature is too high for max regen.

Speaking if max regen, what is the max regen available on the Model Y? The Chevy Bolt maxes out at 70 KW on it's single motor and slow charging battery... that is 15 KW higher than it can accept from a CCS station.

Keith
 

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