R1T Limited Regen Warning: What's normal?

[usulio]

I live on a hilltop, whenever I leave my house, it is a 1,000' decline for the first 3 miles. I leave at 85%, the regen limit light comes on at same spot every time. I wanted to harvest the power as I went down so I tried 15 MPH decent, did not work, same battery regen notice. Then I tried the min. speed for cruse control, 25 MPH. Bingo, the regen limit notice did not come on! The 25 MPH was not too fast for the curves and I gained 3 miles as I drove down.
There is one spot where the road is steep, and the road ahead is interpreted by the auto braking function as something to slow for. The truck auto slows to 17 MPH, I do not mind since the curve is sharp. I then reset the speed to 25 MPH and finish the decent!

I would guess that at the higher speed, more energy was lost to wind resistance instead of recaptured, so the battery was charging slower.

I also guess, like someone alluded to above, the battery just can't absorb more than a certain amount of power in a certain amount of time. These descents are basically like DC fast charging, for example by my math, if you descend 500 feet in a minute of driving, you could be charging at 60 kW.

(Quick calculation: if you descend 500 ft (150m) in a 7500 lb vehicle (3400 kg), that's 150*3400*9.81 = 5 MJ of gravitational energy released, divide by 3.6 to get 1.4 kWh. You lose some to air resistance and friction, so I'll make a wild guess that you can recapture 1 kWh of that. 1 kWh in one minute is a 60 kW rate.)

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[ironpig]

Ok, so maybe normal. Thanks for the reply.

I live at the base of some small foothills so the beginning of my commute every morning is a very low grade downhill. I get the warning every day now. It's annoying, but I guess it's "normal". It started after one of the software updates maybe 3 or 4 updates ago.

It happens regardless of battery state - which is strange.

I used to get a similar warning with a Tesla but only if the battery was at 90-100% which I always figured was because high state of charge limited the amount of Regen energy that could be absorbed back in to the battery. If you start at 100% on a downhill it had to reduce Regen because there was nowhere for that energy to be stored. (Or at least that's what I assumed.). It didn't happen when I was at 80% or lower state of charge.

With the Rivian, it doesn't make any sense. I am hoping it will be "fixed" in an update at some point because it didn't start out this way when I got my truck last year.

 

[Electrified Outdoors]

Full Regen in max Regen setting can Regen at a rate of up to 150kw. If you above 60% state of charge I can't imagine the truck will allow that for too long. As someone else said it's basically like fast charging but remember the motors and inverters are doing more work too.

One might also want to reduce Regen to standard as the net energy put back into the battery may be higher before Regen is limited in these scenarios. This will vary.

 

[tcole]

Full Regen in max Regen setting can Regen at a rate of up to 150kw. If you above 60% state of charge I can't imagine the truck will allow that for too long. As someone else said it's basically like fast charging but remember the motors and inverters are doing more work too.

One might also want to reduce Regen to standard as the net energy put back into the battery may be higher before Regen is limited in these scenarios. This will vary.

That’s very interesting, thanks!

most of my driving is just on all purpose in default settings, so I think standard regen.

How do you know full regen on max is 150kw? And what would standard be?

 

[s4wrxttcs]

I don't have any answers for you, but if this is a location you commonly go to then you might consider testing the following.

Use All-Purpose Mode and see how much regen you get going down when you start at 40%.
Use Conserve Mode and see how much regen you get going down when you start at 40%

I'm wondering if conserve mode is more limited because the regen is taking place with just 2 motors versus all 4. Or if something else isn't limiting it.

Back when I initially got my R1T there was a bit of a hack that allowed people to see some diagnostic screens. I'd love to see what those showed during this regen.

 

[CJdergroße]

Had the same issue, came down from lodgepole campground recently, no chargers up there. Truck got regen warning 90% of the way down, pretty disappointing. Guess the regen heats up the motors too quickly? Was better than nothing. Kept me at a safe speed, still had to use the brakes occasionally, which was the disappointing part, waste of energy.

 

[shap]

There are a couple of youtubes from Kyle about this - in short, he claims that the problem is with invertors, they overheat very quickly and regen will not work - you basically will use your regular breaks, and this will cause significant wear. Unfortunately, it is a hardware limitation, that software can not fix.

Rivian tried to optimize it several times, including in the latest updates (according to Kyle) but the result is still not what you would expect....

 

[VSG]

Full Regen in max Regen setting can Regen at a rate of up to 150kw. If you above 60% state of charge I can't imagine the truck will allow that for too long. As someone else said it's basically like fast charging but remember the motors and inverters are doing more work too.

One might also want to reduce Regen to standard as the net energy put back into the battery may be higher before Regen is limited in these scenarios. This will vary.

Yes.

In short, I don't see anything mysterious about this. Regen is just like DC fast charging - you're taking energy and trying to dump it into the battery, and the rate you can do that is limited by your state of charge, battery pack temperature, etc. whether you're fast charging or braking.

Each Rivian engine can use about 300kW of power, so when braking they can in principle generate a similar amount. Just think of it - if each engine can generate hundreds of kW via regen, that will EASILY exceed what the battery can accept, which is at max only ~220kW.

It is really no wonder that the regen is limited (by the Rivian software) in many situations, ESPECIALLY when making long descents, because the battery pack can only accept a limited amount of power. When your SoC is high, regen will be more limited, and when your battery hasn't been preconditioned, regen will be more limited.

But even in the best case, regenerative braking can generate far more power than the batteries can possibly accept.

These are enormously powerful engines, so comparing it to another EV or PHEV with a much smaller engine isn't reasonable. A Rivian generates so much more power that it's quite expected to see Rivian hit its regen limit when other cars don't. It's not an indication of bad design or anything like that, as some have spun it.

 

[Electrified Outdoors]

Yes.

In short, I don't see anything mysterious about this. Regen is just like DC fast charging - you're taking energy and trying to dump it into the battery, and the rate you can do that is limited by your state of charge, battery pack temperature, etc. whether you're fast charging or braking.

Each Rivian engine can use about 300kW of power, so when braking they can in principle generate a similar amount. Just think of it - if each engine can generate hundreds of kW via regen, that will EASILY exceed what the battery can accept, which is at max only ~220kW.

It is really no wonder that the regen is limited (by the Rivian software) in many situations, ESPECIALLY when making long descents, because the battery pack can only accept a limited amount of power. When your SoC is high, regen will be more limited, and when your battery hasn't been preconditioned, regen will be more limited.

But even in the best case, regenerative braking can generate far more power than the batteries can possibly accept.

These are enormously powerful engines, so comparing it to another EV or PHEV with a much smaller engine isn't reasonable. A Rivian generates so much more power that it's quite expected to see Rivian hit its regen limit when other cars don't. It's not an indication of bad design or anything like that, as some have spun it.

A hot inverter will shut off Regen too. This is one of the difference between a DCFC and Regen.

 

[jwardell]

I got my R1T on June 7th, and I live in Tahoe and pretty quickly noticed I was getting the "Regen Limited' warning.

We just took a long weekend to Mammoth Lakes, and the road into town from where we're staying turned out to be a pretty good and consistent regen test.

We are staying at Tamarack Lodge, which is at 8500 feet, and it's about 2.4 miles from the first stop light in Mammoth Lakes at 7,800 feet. Every time we go down the hill, I get the "limited regen" warning near the bottom. This about matches my experience in Tahoe.

It seems I can only do about a 600 - 700 foot vertical drop before the regen warning comes on, and I can see the limited regen indicator.

I got here with a 49% State of Charge and got down to about 29% before I went and charged. Every time we went down the hill I got the warning. So this is NOT an issue of the battery being too full.

I did have a brief conversation with someone at the Rivian service number, but they didn't know if this was normal or not, and we were mostly focused on addressing another issue.

Is this normal? Or should I try to get Rivian service to take a look?

It sure seems pretty annoying. My Volvo C40 certainly doesn't do this.

This is sadly normal. Of course it's much worse if your charge is in the top 20% or pack is cold, but even at room temp and 70% SOC I will only get about 1/3 down my hill till regen drops to about 30kW. It very much depends on how steep and sustained your hill is, in my case very steep for the first half. I still play a game to see if I can make it to the bottom without using brakes, but I lose if I catch up to anyone not doing 70 through tight turns...

 

[Electrified Outdoors]

That’s very interesting, thanks!

most of my driving is just on all purpose in default settings, so I think standard regen.

How do you know full regen on max is 150kw? And what would standard be?

Taken from Tom article from September of 21. Eventually I would like to be able to pull data from the truck to see what it's doing.

Yes inverters will heat up and shut off regen. There are a lot of things that will affect it. Kyle was also talking about throttled charging speeds as well.

My opinion is that Rivian is being very conservative with these trucks. Having a bunch of failures could ruin the brand. I hope that Rivian is able to tweak things some more once they have more data to work with.

https://insideevs.com/reviews/536129/2022-rivian-r1t-first-drive-review/

 

[domoplaytime]

I get the limited regen warning coming down the slope of Haleakala from 1800' to 80' over 9 miles. The temperature has ranged from the 70s on departure to high 80s on arrival closer to sea level. My SoC was 70% on departure today. Typically the limited regen is still good enough to honor the posted 55 mph speed limit without touching the brakes, and it sure beats sailing downhill at 80+ mph in neutral, or riding the brakes the whole way down like all ICE vehicles do.

 

[shap]

Yes.

In short, I don't see anything mysterious about this. Regen is just like DC fast charging - you're taking energy and trying to dump it into the battery, and the rate you can do that is limited by your state of charge, battery pack temperature, etc. whether you're fast charging or braking.

Each Rivian engine can use about 300kW of power, so when braking they can in principle generate a similar amount. Just think of it - if each engine can generate hundreds of kW via regen, that will EASILY exceed what the battery can accept, which is at max only ~220kW.

It is really no wonder that the regen is limited (by the Rivian software) in many situations, ESPECIALLY when making long descents, because the battery pack can only accept a limited amount of power. When your SoC is high, regen will be more limited, and when your battery hasn't been preconditioned, regen will be more limited.

But even in the best case, regenerative braking can generate far more power than the batteries can possibly accept.

These are enormously powerful engines, so comparing it to another EV or PHEV with a much smaller engine isn't reasonable. A Rivian generates so much more power that it's quite expected to see Rivian hit its regen limit when other cars don't. It's not an indication of bad design or anything like that, as some have spun it.

Rivian regen is 150kW max. I do not think the battery can not handle that, so it is probably more about overheating the inverters.

But anyway, hope they will tweak it a bit, but full solution will not be possible without new hardware IMHO

 

[AxelR]

Same issue here.
Experienced it going to Santa Cruz as well as coming bank back from Bear Valley. Various states of charge (as low as 24% and as high as 95%).
Extremely different experience from our Tesla and will be hard on brakes.

 

[Greg Chick]

This is sadly normal. Of course it's much worse if your charge is in the top 20% or pack is cold, but even at room temp and 70% SOC I will only get about 1/3 down my hill till regen drops to about 30kW. It very much depends on how steep and sustained your hill is, in my case very steep for the first half. I still play a game to see if I can make it to the bottom without using brakes, but I lose if I catch up to anyone not doing 70 through tight turns...

I too have tried to not use the brakes and gone a bit too fast downhill. But keep in mind, tire wear on 21" tires is very expensive! So, I stay in the speed/safe limits and save tire wear, and brake when needed.

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