Regen brake loss

[D.Jeon]

Hey guys,

so I have I 2020 model 3 SR+. I recently noticed that my regen braking only has about 70% power, I did have dots on the bar which have recently disappeared but still only get 70% regen. I contacted Tesla who advised me that because I charge to 90% consistently and my charging range is from 50%-90% it would affect the regen. I was advised to drain the battery to atleast 20% and charge to 90% for a week or two to recalibrate the regen. Also would that mean that I would have to calibrate the regen every so often? I was first told that once my battery reaches below 90% that i should get full regen but was then told I needed to recalibrate?? any knowledge would be appreciated, thanks.

 

[roblab]

Not so much knowledge, but some experience. Regen takes kinetic energy and runs it through the gears to the generator, to push it into the battery. If your battery is near full, or thinks it's near full, the car will not allow energy to be pushed into the battery, which would harm the battery. Also, if your battery is hot or unduly cold, the car will try to protect the battery first, and cut regen.

I'm not sure what they mean by having you recalibrate, but I would guess by what you tell that it would be a one time job. And often you don't get full regen below 90%. It depends on a lot of factors. Mainly, I find that the battery has to be well less than 90% to get full regen. You're cramming electrons into a battery, so being almost full will definitely slow that process, as will a hot battery.

If you're worried about regen, keep your battery nearly empty (!) so it has lots of room to accept those electrons. Or not. If you know your battery is full-ish, don't go trying to cram energy into it. Just expect that regen will be reduced.

 

[jjrandorin]

You will not have full regen anytime you have dots showing. That shows that your battery can not take full regen, usually because its too cold to (the battery). To preemtively answer the usual next question, yes the battery can be cold even if its 70 degrees outside, or even 70 degrees in your fully enclosed garage.

Never heard of calibrating regen, they were giving you the standard answer about the battery, probably because they answer 200 questions a day that start with "I dont understand why My car only charges to XXXX" or "I dont understand why I drove 100 miles buy the car lost 140 miles".

 

[sroy]

My understanding is that to maximize battery life you should keep the battery between 50-80/90% but if your driving habits are such that you rarely go below 20-60%, while battery lofe is better overall, the software “knows” less the battery so it’s accuracy is lower. The comprise is to go one week out of every month or every other month without charging. Not sure if that’s related to regen or not.

 

[jjrandorin]

My understanding is that to maximize battery life you should keep the battery between 50-80/90% but if your driving habits are such that you rarely go below 20-60%, while battery lofe is better overall, the software “knows” less the battery so it’s accuracy is lower. The comprise is to go one week out of every month or every other month without charging. Not sure if that’s related to regen or not.

Thats a nice summary of about 150 pages of battery threads . AFAIK, regen is really only impacted by the batteries ability to take a charge, either because "its too cold (the battery), or "its too full".

 

[D.Jeon]

Not so much knowledge, but some experience. Regen takes kinetic energy and runs it through the gears to the generator, to push it into the battery. If your battery is near full, or thinks it's near full, the car will not allow energy to be pushed into the battery, which would harm the battery. Also, if your battery is hot or unduly cold, the car will try to protect the battery first, and cut regen.

I'm not sure what they mean by having you recalibrate, but I would guess by what you tell that it would be a one time job. And often you don't get full regen below 90%. It depends on a lot of factors. Mainly, I find that the battery has to be well less than 90% to get full regen. You're cramming electrons into a battery, so being almost full will definitely slow that process, as will a hot battery.

If you're worried about regen, keep your battery nearly empty (!) so it has lots of room to accept those electrons. Or not. If you know your battery is full-ish, don't go trying to cram energy into it. Just expect that regen will be reduced.

thank you. Even at 60% below I don't get full regenbut i will try to "recalibrate"

 

[jjrandorin]

thank you. Even at 60% below I don't get full regenbut i will try to "recalibrate"

There is no "calibration" needed for regen. You wont get full regen if your battery is cold, no matter what percentage charge you are at, and your battery will be cold when you first get into it pretty much no matter what the temperature is, unless it JUST finished charging.

All the calibration stuff is for battery capacity, not regen.

 

[Gauss Guzzler]

All the calibration stuff is for range estimation, it has no effect on the battery or the car's behavior in any way. It's just a way of improving the accuracy of the range estimate icon on the screen.

The battery needs no care but as the car will notify you, it's preferable to stay in the 20-80% SOC range if convenient. And as others have noted, a cold full battery will have reduced regen ability.

 

[iaflyer]

Also, what you think is "not cold" for Toronto is still cold for the car and battery. I live in Michigan, so anytime this month (May) the car has been below 65 degrees F overnight I still get .... showing on the Power meter at 90%. Once I've driven some, used some battery and the battery pack warmed up, the regen kicks in to maximum.

 

[ZapCarM3]

thank you. Even at 60% below I don't get full regenbut i will try to "recalibrate"

Do you ever experience this without the dots?

 

[nickbatz]

We got reduced braking earlier this week, and the battery was not close to full.

It has been colder in Los Angeles, maybe 65˚, but this was after driving on the freeway for several miles.

What's going on?

 

[Gauss Guzzler]

Yeah the battery is just really timid, especially early in the drive. I find that even in temperatures of ~80F and SOC ~80% I only get about 10-20 seconds of strong regen before it gives up and displays the warning. But then it starts working again within a few minutes.

I'd guess that it's doing something more sophisticated than simply measuring the pack temperature since the pack surely can't warm up significantly within a few minutes. Perhaps it needs to monitor the pack performance (e.g. internal resistance, cell balance under load, etc.) for a few minutes at the start of each drive and doesn't want you to do too much regen until it's sure the pack can handle it without degradation.

 

[GtiMart]

You're in Toronto, the main answer is "cold battery". Even if it's at 20% SOC, if it's cold, your regen will be limited. I do not get full regen until the battery is somewhere between 10C and 16C, something like that. I'm talking battery temperature, not outside temperature. The battery is a big mass and does not heat up quickly. Driving the car barely generates enough heat in the motors to get it to that temperature after a (long) while in the winter. I do not have a heat pump so YMMV a bit.
If you condition the cabin, the car will actively heat the battery up to a point. I think it stops around 5-6C but I need to do more tests this winter as it has changed from previous years.

Yes, there is a "sophisticated" algorithm for regen. You know, regen can go up to 85kW. Normally the battery would want to be at 30-40C to accept this in supercharging, and the charging curve would only accept 85kW of charge power up to around 70%SOC maybe... Regen isn't continuous, it's for short periods so the car accepts it at lower temperatures and higher SOCs, but only for a short period. I can see my max regen value go down (on ScanMyTesla) as I go down a significant hill. It starts going back up slowly when I'm stopped, and goes up faster when I accelerate. Once the battery is low and warm enough, the 85kW max regen stays without budging.

 

[nickbatz]

Thanks, but I'm in Los Angeles. It was in 65˚F range (that's about 17˚ C using the rough translation method).

Still, you may be right that it's the temperature, because it has been a little cooler here the past few days.

 

[GtiMart]

Ah, the OP is indicated as in Toronto, sorry. Nights might be cooler so the battery would drop and be colder than ambient in the morning.

 

[Gasaraki]

Hey guys,

so I have I 2020 model 3 SR+. I recently noticed that my regen braking only has about 70% power, I did have dots on the bar which have recently disappeared but still only get 70% regen. I contacted Tesla who advised me that because I charge to 90% consistently and my charging range is from 50%-90% it would affect the regen. I was advised to drain the battery to atleast 20% and charge to 90% for a week or two to recalibrate the regen. Also would that mean that I would have to calibrate the regen every so often? I was first told that once my battery reaches below 90% that i should get full regen but was then told I needed to recalibrate?? any knowledge would be appreciated, thanks.

90% charge will cut down on your regen a bit. Once you get to 80% you should see full regen again. Temperature will affect this also.

 

[nickbatz]

So I think I've figured something out (because the temperature and 90% full charge situation doesn't apply to me): each time the regen slowed was after a long downhill run.

Ergo there must be a limit to how fast the battery can charge from regenerated electricity, so it stops temporarily when you reach the limit. My guess is that there's a buffer that fills up, after which it stops accepting more juice.

 

[AlanSubie4Life]

So I think I've figured something out (because the temperature and 90% full charge situation doesn't apply to me): each time the regen slowed was after a long downhill run.

Ergo there must be a limit to how fast the battery can charge from regenerated electricity, so it stops temporarily when you reach the limit. My guess is that there's a buffer that fills up, after which it stops accepting more juice.

Yes this is correct, though the buffer is more of a electrochemical one than a separate place where charge is stored. It takes time for intercalating to be complete, so I think what happens is there is initial a fair amount of open spots for the lithium ions (which provides the rate limit to prevent lithium plating), but as those fill up, there is probably additional diffusion from the outer layers to the inner layers that must take place in the anode to make room for additional intercalation. This is slow and then that becomes the new (lower) rate limit.

Just speculative of course.

But it would explain your correct observation that regen actually decreases if you have done regen recently - even if the battery is warming up a bit and the SOC has not changed significantly. This behavior is very apparent on hills. I never notice it anymore though since I am now setting my charge limit to 60-70% maximum and I live in a warm area.

 

[nickbatz]

Yeah, I'm in Los Angeles (Sherman Oaks, about the same temp as SD), and the charge was nowhere near full - point being that it's almost certainly the amount of regen it can eat all at once, not the maximum charge limit.

As an aside, we set our charge limit just below the default (227 miles). That's 88% according to the app, probably 80% according to reality.