Regen Brakes Auto Disable on steep road?

[Kacey3]

I've seen regen reduced both for cold and for "excess regen." They had different icons and different warnings. As I understand it, the truck can only regen energy so quickly so if you are descending for an excessive amount of time, then you will get limited regen braking until you level out or go back uphill. When we visited Pike's Peak, we hit the regen limit pretty darned quick when we were coming back down the mountain.

It wasn't until a day or too later that it was so cold out that we suffered limited regen again, but this time it was the snowflake icon and a warning about the battery being too cold.

And then, of course, there's the third reduced regen, which comes from having a battery charged to over 80%.

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[s12dxer]

This happens to me in the mountains, both warm and cold temperatures. If I regen for too long, it's almost like it needs to relax or cool down a bit before I get full regen back. It always comes back in a few minutes. I get some, just not full. The regen gauge on the righthand side will actually show a portion of the top end of the range as "crossed out" and thats how you can tell your regen is limited.

My truck's behavior is identical to what you've described...

 

[EzMev]

I get reduced regen in 3-5 minutes going downhill at 45-65 degrees ambient every time...I was really surprised how little it takes. In fact I thought there might be an issue w/ my R1S regen ability, but from the forums here is said to be normal. Seems pretty odd to be, but I am guessing some sort of heat/inverter issue?

 

[Cosmacelf]

I just experienced this today coming down from Big Bear Lake. Annoying. My Tesla Model X does not do this at all. I suspect it has to do with the single cooling/warming plate that is sandwiched between the two battery layers. Top layer gets too warm while the bottom gets too cold since it is exposed to the cold air, and the Rivian can’t heat the cold layer since it would warm up the hot layer too much.

Similar to what’s happening with DC fast charging when the Rivian’s can’t charge fast and yo yos between fast and slow charge rates in cold temperatures.

Regardless of WHY, it is most definitely a design problem.

 

[WSea]

In my experience, each update has made it a bit worse. With the latest update it seems much better and haven’t received any low regen warnings

 

[VSG]

And then, of course, there's the third reduced regen

Again, no such thing as multiple types of reduced regen. Regenerative braking works by charging the battery. The battery has a charging curve. You can only "regenerate" as much energy as the battery will accept at that time. You're familiar with the charging curve - the maximum rate of charge is when the battery is less than about 60%. Above that, charging rate is reduced. So is regen, for the same reason. Likewise, when the battery is cold, charging rate is reduced. So is regen, for the same reason. And when going down a steep road, the regen braking can generate FAR more power than the battery pack can accept. So regen is reduced.

It all comes down to how much energy the battery pack can accept. Generating more than that through braking is a problem, because where would all that current go if it can't go into the battery?

 

[boredcleaner]

This happens to me often. I live in a hilly area and going downhill I'll get the regen reduced notice and will need to use the brake.
I don't what's happening behind the scenes, but my assumption (pure speculation) is that regen dumps power into a holding area that gets fed into the main battery. When that holding area fills faster than it can dump into the main battery it stops regen.
Would like to know if someone with more facts has info.

I experience this situation every day. I live on a hill and cannot make it to the bottom without the warning. It clears quickly on my few minutes of flat, but comes back almost immediately on my next sustained (a minute tops?) downhill. There is something wrong with either the regen algorithm or something in the Bosch inverters. Battery warm, cold, hot makes no difference. Battery full, mid, or empty makes no difference. A few moments of regen and the warning comes on. I hope they are looking at this issue, it seems like an obvious bug.

 

[Riviot]

It all comes down to how much energy the battery pack can accept. Generating more than that through braking is a problem, because where would all that current go if it can't go into the battery?

Flux ...

Capacitors.

 

[VSG]

You know, I *was* thinking that ... it takes energy to go back in time .... but that only happens at 88 mph IIRC.

 

[Rivan]

The only thing I can think of is this, since the truck is heavy, coming down hill, will generate more than what the Regin can handle and causes heat. I was watching youtube of someone who was testing "tow charging".. according to him, the rate of charge is very high if the truck is pulled and let it regenerate.. It is possible they auto set that to reduce it and protect the components..? other than that i am still confused, but it looks most of us have seen this ..

 

[Kacey3]

Again, no such thing as multiple types of reduced regen.

All I was saying is that there are three different errors that will warn you that the truck will exhibit reduced regeneration.

 

[MoreTrout]

Good question. I'm probably making stuff up from watching too much Star Trek as a kid or something.
I definitely don't have a good understanding of what goes on "under the hood" in an EV.

First time I read through this thread I thought a capacitor or something functioning like it was extremely unlikely, but I had something odd happen the other day. I came down what is probably the steepest hill I occasionally drive up and down. It probably isn't even a mile, and I don't expect to make it halfway before regen becomes limited, but I'll add at least 1% and 2 or 3 miles to the GOM on the way down. What was odd was the next 4 or 5 miles of flat 60mph driving. The efficiency meter on the left remained completely pegged at the top and not a single mile or % decreased. I was actually getting worried it might have failed and was stuck. I know the efficiency meter isn't immediate, but I always drive with it and it is pretty responsive with changes in slope or speed minute to minute. It sure acted like that steep hill produced regen that continued for the next several miles on a flat surface.

 

[WSea]

First time I read through this thread I thought a capacitor or something functioning like it was extremely unlikely, but I had something odd happen the other day. I came down what is probably the steepest hill I occasionally drive up and down. It probably isn't even a mile, and I don't expect to make it halfway before regen becomes limited, but I'll add at least 1% and 2 or 3 miles to the GOM on the way down. What was odd was the next 4 or 5 miles of flat 60mph driving. The efficiency meter on the left remained completely pegged at the top and not a single mile or % decreased. I was actually getting worried it might have failed and was stuck. I know the efficiency meter isn't immediate, but I always drive with it and it is pretty responsive with changes in slope or speed minute to minute. It sure acted like that steep hill produced regen that continued for the next several miles on a flat surface.

I've noticed the same thing. Not sure which recent update made this change. Assuming it is showing the regen charge as part of the efficiency

 

[Deleted member 11292]

Hopefully this is a software fix, because not having access to any "engine braking" while towing down hill is a very bad thing.

 

[rhumbliner]

This happened to me with the battery warm and SoC at 63%. The message said regen reduced due to high SoC. I punched the emergency flasher to mark the log and then called support and asked them to analyze the log. I was told it was due to the battery overheating as it was being re-charged. Apparently the BMS can’t cool the battery quickly enough. When I asked why the message doesn’t explain it’s an overheating issue she said this was a catch-all message.

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