Unusual regenerative breaking behavior

[GratefulMed]

Tried posting this earlier today but doesn’t look like it went through so I am trying again.

Experiencing a new unusual regenerative breaking behavior. Here in Kentucky, we’ve had a few bouts of pretty cold weather over the past month. Previously, with temperatures in the 20s, I would frequently get the warning message that regenerative breaking would not function well which then disappeared as the car warmed up. Over the past few weeks, however, I no longer get that message. What I am now experiencing is occasions where the regenerative breaking seems to just give up anfter initially seeming to function. At slow speeds below around 25 mph, it works normally. If begun at speeds around 30 mph, however, it initially works to slow down the car and then just suddenly stops and the car begins to coast and you have to apply the break pedal to slow down at all and to bring the car to a halt. This is most prominent going downhill towards a stop sign. You can just feel the breaking suddenly no longer working. When I look at the regenerative graphic, it seems like the regenerative zone is smaller than when it is functioning correctly. After stopping, it acts normally while driving slowly but the same issue occurs again a few minutes later. During these episodes, I get no warning about the regenerative breaking not being available in cold weather. And, in fact, this is occurring long after I’ve begun driving when the car is completely warm. Any ideas as to why this is happening and what it means?

 

[DeaneG]

It probably detected a loss of traction (too much regenerative braking for slippery conditions). When it does this, you'll lose regeneration for a bit. Not sure when it turns back on.

 

[borski]

Tried posting this earlier today but doesn’t look like it went through so I am trying again.

Experiencing a new unusual regenerative breaking behavior. Here in Kentucky, we’ve had a few bouts of pretty cold weather over the past month. Previously, with temperatures in the 20s, I would frequently get the warning message that regenerative breaking would not function well which then disappeared as the car warmed up. Over the past few weeks, however, I no longer get that message. What I am now experiencing is occasions where the regenerative breaking seems to just give up anfter initially seeming to function. At slow speeds below around 25 mph, it works normally. If begun at speeds around 30 mph, however, it initially works to slow down the car and then just suddenly stops and the car begins to coast and you have to apply the break pedal to slow down at all and to bring the car to a halt. This is most prominent going downhill towards a stop sign. You can just feel the breaking suddenly no longer working. When I look at the regenerative graphic, it seems like the regenerative zone is smaller than when it is functioning correctly. After stopping, it acts normally while driving slowly but the same issue occurs again a few minutes later. During these episodes, I get no warning about the regenerative breaking not being available in cold weather. And, in fact, this is occurring long after I’ve begun driving when the car is completely warm. Any ideas as to why this is happening and what it means?

Is it icy on the road where you are? If so, the Air is trying to save you from a downhill skid. This isn’t limited to Lucid; it happens in any car when traction control prevention kicks in. When the car detects a loss of traction, torque commands diminish drastically to make sure traction is recovered, to permit steering inputs. In acceleration, the torque reapplication happens quite quickly, but in regen, the torque reapply takes a longer time, because the system used is an off-the-shelf system developed for combustion engine vehicles which don’t have regen.

The Sapphire and RWD Pure don’t have this problem, as they use Lucid’s in-house traction control system instead. My understanding is that this will eventually come to other Airs too, but they want to perfect it first. Don’t quote me on that last part.

 

[GratefulMed]

This is occurring on parts of roads that have no snow or ice (though there is plenty around) and I don’t think I’m seeing any traction control warning signal - but it’s possible there’s minor ice I’m not noticing. Once it gives up, it doesn’t kick back in until I’ve hit the accelerator or fully stopped. Just coasts. And mine is a 2024 Pure RWD. I guess traction loss must be the culprit, but it is interesting that I have not seen the low temperature regenerative warning despite the low temperatures outside. Made me wonder if it is a sign that something more serious is going on.

 

[borski]

This is occurring on parts of roads that have no snow or ice (though there is plenty around) and I don’t think I’m seeing any traction control warning signal - but it’s possible there’s minor ice I’m not noticing. Once it gives up, it doesn’t kick back in until I’ve hit the accelerator or fully stopped. Just coasts. And mine is a 2024 Pure RWD. I guess traction loss must be the culprit, but it is interesting that I have not seen the low temperature regenerative warning despite the low temperatures outside. Made me wonder if it is a sign that something more serious is going on.

That’s unusual. If it’s not happening where there is any loss of traction, something else may be going on.

 

[SaaSManKS]

I have this exact same thing happening to me, and I notice it most when I'm coming out of my garage in the morning onto a flat no ice driveway...I thought ti was a weird assimilation with the unusually cold weather too, but my car is going in (shocking I know) so I added it to the ticket for them to look at it while it's there.

 

[segbrk]

This happened to me while slowly reversing yesterday. Like you said, regen didn't kick back in until I had fully stopped with the friction brakes. I was definitely on snow/ice, but I've never experienced that before.

 

[Electrified]

This is occurring on parts of roads that have no snow or ice (though there is plenty around) and I don’t think I’m seeing any traction control warning signal - but it’s possible there’s minor ice I’m not noticing. Once it gives up, it doesn’t kick back in until I’ve hit the accelerator or fully stopped. Just coasts. And mine is a 2024 Pure RWD. I guess traction loss must be the culprit, but it is interesting that I have not seen the low temperature regenerative warning despite the low temperatures outside. Made me wonder if it is a sign that something more serious is going on.

What state of charge is the battery at when this happens? I ask this because I notice that the regen braking in my car isn't as aggressive as it when temps are above freezing, I attribute this to how the regen gets weaker when the battery is charged above 80% in warmer weather.

 

[mraschko]

This sounds like an issue I've been dealing with for two years now. In November, I restarted a dialog with service about the issue. Here is my description I gave to them:

First, let me explain that this is not a new issue. I complained about this last fall/winter/spring but we were not able to come to any resolution. The problem stopped occurring shortly before the regenerative braking warning was rolled out. There definitely is a temperature element to this as I did not encounter it all summer. That said, this does not happen all the time nor is it as simple as "below temperature x, it will occur".

When it does occur, here is what currently happens. Backing out of my garage, I will see the warning that regenerative braking is reduced. This is the text warning that occurs briefly. I charge my car to 80% over night and to the best of my recollection, this is the state of the vehicle when this occurs. I have been having a reliability issue with scheduled charging (sadly not fixed by 2.5) so it is possible that it might have occurred with a lower state of charge and I'm just not remembering.

My neighborhood is relatively flat. As I drive out of the neighborhood, I don't typically notice any reduction in regenerative breaking, but I can't say for certain that I have not ever noticed any reduction. There are 1 to 3 stops (depending on traffic lights) that I need to make before the problem occurs where I could have a reduction. This portion of the drive is several minutes long and about 2.5 miles.

After this, I have an approximately 1 mile descent. Near the end of this descent, I will encounter NO regeneration. I am completely reliant on the brake pedal to slow and stop the vehicle. Since the indicator of regenerative braking has been released, I've watched it shrink to nothing while this occurs. It starts with something like half available and by the time I'm at the bottom of the plateau, it is completely gone. This is what I was attempting to show in the picture. I can't take a video for safety reasons and as I stated earlier, this does not happen every time so I don't just have someone ride along with me to video either. Within a few minutes (maybe as much a 5 - 10 but often less), regenerative braking is restored.

I think I have the temperature in the vehicle set to either 68 or 69 degrees, so as you say, it's likely the heater was active and based on the picture the car is using some power.

After a few exchanges here is what service came back with:

My apologies for the delay in response time but I wanted to follow up on this. After careful review of the data with field service engineering, this looks like it might be temperature related. Not so much ambient temperature but the temperature of the battery and drive units. With what you described, it sounds like it is happening after the vehicle has been sitting for an extended period of time. Do you normally pre condition the vehicle prior to your drives? Has it been occurring on a more consistent basis recently now that the temperature has dropped significantly?

Would you be okay with trying preconditioning your vehicle for about a week to see if the issue persists? Please let us know at your earliest convenience, thank you!

This has mostly worked for me but I've had a few cases where it hasn't. I've shared this with Lucid and am waiting to hear back.

 

[Pragmatic]

I wrote about similar experiences last year. Of course then there was no warning about limited regen. But the times I've lost it it was after 5 - 10 miles with heavy use if regen, cold battery, cold drivetrain. I have nor made many trips yet this year so I have nothing more to add.

Post in thread 'Regenerative braking'

P

Post in thread 'Regenerative braking'

May 9, 2024

I have lost regeneration twice, both in roughly the same place.

When I go skiing I stay at a house near the base of the hill. Twice when leaving, temperatures in the mid 20s F, SOC around 50%, I lost regeneration approximately 6 - 8 miles after leaving to go home.

The drive is up ~10% grade for a gain of about 700 feet over ~ 1.5 miles, then down grades between 0% and 13% for a total loss of 2000 feet over ~6 miles. During maybe the fifth downward pitch I would lose all regeneration. I drive in swift with minimum regeneration to limit braking on slick surfaces.

I've taken it as a cold...

• Pragmatic

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[SaaSManKS]

What state of charge is the battery at when this happens? I ask this because I notice that the regen braking in my car isn't as aggressive as it when temps are above freezing, I attribute this to how the regen gets weaker when the battery is charged above 80% in warmer weather.

I've noticed it happening multiple times after unplugging my car from charging at home to 80%