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At what temp is decreased regen braking noticeable

SigNC

Active Member
Aug 23, 2017
1,631
1,546
NC
It really depends on what car you have. the SR will see it before the MR and MR before the LR RWD. LR AWD might be about the same as MR but it also has stronger regen in general. It's really just a factor of how much energy your battery can take vs how much regen your model of car puts out at max regen. In my AWD I'll sometimes see it as early as 65-70 degrees at 80% charge. Of course it quickly goes away. I would say it's pretty much norm once it's in the 60s and the car has been in those temps overnight. Further into the limitation it is the longer it takes to go away. Also, this is the first winter where the 3 will have on route battery warming so overall it should be MUCH better as far as charging goes.
 
Anytime the car sits overnight below 60F I see a few dots over on the left (regen somewhat limited). You don't really notice it until it gets down below 40F and you start getting more dots. During winter here in MN the dots completely fill the left side. On short trips it never warms up enough to get good regen. When the outside temp gets below 0F you probably won't be able to get it warm enough for full regen.

This is not always a bad thing. The lower regen helps in slick conditions. Less likely regen will make the wheels slide.

It varies how long it takes to get full regen back. Depends on the outside temp and length and speed of driving. You can help warming the battery in the morning by timing your overnight charging to finish about the time you normally use the car.
 

Phlier

Bluebird
Jun 12, 2019
2,281
4,343
Utah
It isn't just temperature that determines regen ability, it's the combination of state of charge and temperature.

You can have limited regen when it's 100f outside, with a state of charge >90%

You can have limited regen when it's 0F outside, with a state of charge of 50%

It's best not to worry about it, and just let the car's programming take care of it. :D
 
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Also it can even become limited with a warm battery at 50% charge if it's being used excessively, like if you're descending down a mountain for miles at a time.
Does this ever become a serious problem to the point of brake fade?

ICE cars can use engine braking to limit brake use on long mountain passes, and the engine braking can continue without any ill effects. If regen goes away on a mountain pass, the friction brakes won’t last very long on our heavy cars.
 
Does this ever become a serious problem to the point of brake fade?

ICE cars can use engine braking to limit brake use on long mountain passes, and the engine braking can continue without any ill effects. If regen goes away on a mountain pass, the friction brakes won’t last very long on our heavy cars.

Considering the otherwise limited use of brakes, I can't see having to use our brake pads on the few occasion regen braking isn't available to be much of an issue.
 

Dr. J

Active Member
Aug 23, 2017
1,478
2,737
Fort Worth, Texas
Does this ever become a serious problem to the point of brake fade?

ICE cars can use engine braking to limit brake use on long mountain passes, and the engine braking can continue without any ill effects. If regen goes away on a mountain pass, the friction brakes won’t last very long on our heavy cars.
Don't charge to 100% (or even 90%) at the top of the mountain, and you should be fine.
 
Does this ever become a serious problem to the point of brake fade?

ICE cars can use engine braking to limit brake use on long mountain passes, and the engine braking can continue without any ill effects. If regen goes away on a mountain pass, the friction brakes won’t last very long on our heavy cars.

Never a serious problem in my experience, but I'm curious as to how they plan to manage regen braking limit on the Tesla Semi where it's critical.
 
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T
They will actively heat the battery. Semis don’t take as many short trips as cars do, so the impact to range and efficiency should be minimal.
The issue is that trucks have tremendous potential energy at the tops of hills, far exceeding the ability of friction brakes to manage a controlled descent on steep grades. Engine braking is much more critical for them than for cars due to the different ratio of mass to braking effectiveness.

Trucks will have to manage their battery usage very carefully in mountainous terrain. They need enough of a charge to get to the next destination, but also enough battery depletion to absorb the potential energy into the battery when descending.

I just realized there is one other option if there is too much potential energy for the batteries to absorb. They could dump that energy into a large set of resistors to simply generate heat that is vented away.
 
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Big Earl

bnkwupt
Supporting Member
Jul 12, 2017
7,368
14,742
Springfield, VA
T

The issue is that trucks have tremendous potential energy at the tops of hills, far exceeding the ability of friction brakes to manage a controlled descent on steep grades. Engine braking is much more critical for them than for cars due to the different ratio of mass to braking effectiveness.

Trucks will have to manage their battery usage very carefully in mountainous terrain. They need enough of a charge to get to the next destination, but also enough battery depletion to absorb the potential energy into the battery when descending.

I just realized there is one other option if there is too much potential energy for the batteries to absorb. They could dump that energy into a large set of resistors to simply generate heat that is vented away.

I’m not sure why that’s an issue. The battery pack can be top-locked so there is always storage space available for regen. Actively heat the battery before the start of the day’s work and you’re good to go. The heating can even be done from shore power so that no range is lost.
 
I’m not sure why that’s an issue. The battery pack can be top-locked so there is always storage space available for regen. Actively heat the battery before the start of the day’s work and you’re good to go. The heating can even be done from shore power so that no range is lost.

It can be an issue because the energy can exceed the ability of the battery to absorb it.

But looking at this a bit further, I found a page that describes this exact scenario, including the resistive heat: Tesla Semi Trucks Won't Use Runaway Truck Lanes As Often As Others | CleanTechnica

One question that could be asked is whether regenerative braking will be sufficient to brake an 80,000 pound, fully loaded semi truck. Well, let’s look at something else that uses electric traction motors to provide braking: 8 million pound diesel-electric freight trains. They use something called dynamic braking instead of regenerative braking. All that really means is that the electricity generated from braking has nowhere to go on a diesel-electric freight train, as the electricity for the motors is supplied by a massive diesel generator instead of a battery. As a result, they route the electricity into heating coils on the roof of the locomotives.
 
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Big Earl

bnkwupt
Supporting Member
Jul 12, 2017
7,368
14,742
Springfield, VA
It can be an issue because the energy can exceed the ability of the battery to absorb it.

But looking at this a bit further, I found a page that describes this exact scenario, including the resistive heat: Tesla Semi Trucks Won't Use Runaway Truck Lanes As Often As Others | CleanTechnica

That shouldn't be a concern unless you're starting at the top of a steep hill with a full battery. As I said, top-locking the battery can ensure enough storage is available to provide regen down the hill. Or, as a professional driver, you can assess the situation and make sure you aren't charging to too high of a state of charge for the situation. Some training will be required.
 

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