Regeneration Concerns

[joesiple]

I've been an EV driver for 10 years and love my new "max pack" R1T. However, I have serious concerns about the break regeneration system. Specifically, the fact that regeneration is decreased so frequently and so suddenly.

For example, on a drive down the mountains from Summit County to Denver last weekend, my R1T had "decreased regeneration" for almost half the drive. It seems like a huge waste! And when I was doing 70 mph down a 7% grade and the truck sped up out of the blue, while simultaneously beeping a warning at me that the brake regeneration was decreased, it was actually dangerous.

There's also reduced regeneration basically any time the battery is over 80%. For comparison, I put 100,000 miles on a Chevy Bolt and never had any of these issues. There was decreased regeneration when the battery was at 100%, but it would be back to normal at 99% and never decrease again...even on the entire drive down I-70 from Summit County. It would gain miles and miles of range...many more than the R1T. Does Chevy just have a better battery? Better technology of some sort? Why can't Rivian accomplish with the R1T what Chevy has accomplished with the Bolt?

I'd love to see much better overall regeneration...and at the very least, a 2-second warning before decreased regeneration happens so it's not so jarring. I actually felt out of control when the truck sped up without warning (or simultaneous warning, which feels the same when driving).

Anyone have similar experiences? Any idea what can be done about it? Maybe an OTA update of some sort?

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[evguy]

I think regen is typically going to be weaker/more limited in the winter, but if the truck isn't warning you at the start of your drive, that's a problem that could be worth a service ticket. That's typically when mine issues the first warning.

As for the Bolt comparison, I'm no expert on battery chemistry. But given the extremely higher mass of the Rivian, it might never be apples to apples.

 

[rhumbliner]

This problem has been discussed in another thread. Rivian explained that the battery overheats during prolonged regen and has to turn regen off. The result of an inadequate battery thermal management system.

 

[Dark-Fx]

Chevy Bolt and never had any of these issues. There was decreased regeneration when the battery was at 100%, but it would be back to normal at 99% and never decrease again...even on the entire drive down I-70 from Summit County

Lol, bullshit. I say that as a previous Bolt owner.

 

[DevSecOps]

I experience the same issues and yes they are more prominent in colder climates/times. I've owned 4 different EVs and the other ones haven't had the same behavior as the R1 when it comes to regen. In my experience it's unique to Rivian. As you've mentioned other vehicles might have it at the start or high SOC, but it doesn't randomly happen when driving.

I would agree with the OP that it's disturbing especially when it happens unexpectedly when you're slowing down. I wouldn't be surprised if it's subject to a recall at some point because unintended acceleration and braking events have been a part of many recalls in the past with EVs.

You should however be receiving an alert at the beginning of the drive and it should also alert you if it changes while driving. Admittedly, most of the time it doesn't get my attention so it's easy to miss when driving.

 

[Zoidz]

SInce it is all software, Rivian could do anything they want to with regeneration. The current behavior isn't by accident, it's by design. I assume they have specific engineering beliefs/ideas/reasons/rationale. We don't know what that is so we compare it to something we know.

The problem with comparing it to your Bolt (or any other vehicle) is the obvious - the Rivian not a Bolt. It's got four 200+ hp motors, it weighs 7000 lbs, etc. The physics of the regen characteristics are way different. Those 4 big motors are generating a lot of power during regen (over 4 times your Bolt regen) but the inverters can handle only so much heat and the battery can recharge at only a certain rate. It's fair to assume that Rivian engineers know a wee bit more about it than we do, and have thought about this quite a bit, and arrived at what they believe is optimal for the vehicle. It's not something we are going complain about and get a drastic fix via OTA for something that isn't broken.

I have experienced it. My commute goes from 920 feet to 250 feet elevation. It does not bother me, I am used to it. But I do agree that if you have full regen, and they are cutting it dynamically, the alert could be displayed a few seconds before it cuts back.

 

[joesiple]

Makes sense, and thanks for your reply! It's a little disappointing to realize the regen situation is sub-par when compared to the Bolt...but I completely understand that Rivian is a different beast with different physics (which I don't make any claim to understand) and we're getting a lot more overall than from the Bolt (obviously). I'll just have to live with the regen situation. But a 2-second warning would take the "dangerous" part out of the equation.

 

[dleepnw]

i agree that they need to provide more early warning. its not helpful or useful if the warning and the lack of regen happen at the same time and i could see someone getting rear-ended due to this. for me, its always happened when going downhill, the temps were in the 30s/40s and the battery was not "warm enough" (id say the battery temp was roughly below 45 degrees F).

the low battery temp/ reduced regen warning rarely comes on when i first start driving even though the temps have been pretty much the same for 6-7 week. id say over that time period, i got the warning 3-4 times when i started my drive and the sudden lack of regen 7-8 times. which means i was ready 3-4 times while going downhill and the other times i wasnt. in other words its inconsistent at multiple levels.

my issue isn't lack of regen when its cold or hot. totally get that. its the way they designed the warning system. its inconsistent and not early enough.

 

[Zoidz]

This problem has been discussed in another thread. Rivian explained that the battery overheats during prolonged regen and has to turn regen off. The result of an inadequate battery thermal management system.

Can you point to where Rivian specifically said that?

There's more to it than that. Rechargeable batteries have something called the C Rate (Charge Rate) that should not be exceeded or it will damage the battery. As the battery charges, the rate must be reduced. Those 4 Rivian motors acting as generators can pump a heck of a lot of power into the battery pack, easily exceeding the C Rate, so Rivian has to limit regen. The graph below illustrates a typical charge curve (dashed line). If the temperature is higher and the SOC is low, the battery can take a higher level of charge. If the battery is cold, or it has a higher level of charge, the rate must be limited so as not to dmage the battery.

 

[VSG]

Regenerative braking has the same limitations as charging. When you use regen, you are actually using the motors to generate electricity and dumping it into the battery pack. So just like charging, if your battery pack is pretty full, it can't accept a high rate of charge OR a high rate of regen. Likewise if it is cold, etc.

A Rivian has four motors which can produce more electricity than the battery pack can take under most circumstances. If you change to Conserve mode with just two motors, then there is less electricity produced and you won't run into the limitations as often. Comparison to a Bolt is silly because that has less than 1/4 the HP of the Rivian and I doubt that the Bolt's one little motor can ever generate enough electricity to exceed the Bolts charge capacity.

Yes it does seem like a waste at times. The way to improve it would be to improve the Rivian's charge rate, which is best-case about 220kW. It this were increased then a lot more of that regen energy could be used. 800V will help, improved thermals will help, decreased HP (e.g. in the Dual motor) will help. But these are future improvements. I think Rivian has done an exceptional job with their first model of balancing all the variables and costs, and their next iterations will only be better.

And when I was doing 70 mph down a 7% grade and the truck sped up out of the blue, while simultaneously beeping a warning at me that the brake regeneration was decreased, it was actually dangerous.

IMO that was just your perception. The vehicle is not speeding up - the braking was reduced just as if you had eased up on the brake in your ICE vehicle while heading down the hill. You FELT this and it SEEMED like you sped up, but I doubt you changed speed by more than 1 mph before you reacted. I would guess that mostly you were taken by surprise, having not encountered this before, and next time you will recognize the beep and the feeling and not think twice about it. You natural reaction was probably to start braking, which is exactly what you would do with an ICE if you felt it going faster as a down hill grade increased, so your Rivian isn't asking you to do anything you wouldn't have instinctively done anyway. I don't see this as anywhere near a safety issue.

 

[MrMusAddict]

What I don't get is why they don't blend the friction brakes to simulate regen when normal regen is limited. Genuine safety concern when I barrel down a hill and all of a sudden I ACCELERATE towards the car in front of me. The first time that happened, it was unnerving. They normally hide the weight of the vehicle really well, but with regen limited it felt like I was in a tank about to careen off a mountain road at 50 mph...

 

[joesiple]

I guess we'll have to agree to disagree on some of this (and that's okay!)

If I'm expecting the vehicle to act one way (to continue it's current regeneration) and it doesn't, it's dangerous, in my opinion. Maybe it actually speeds up, maybe it doesn't. But when a vehicle changes the way it's behaving without advanced warning, I consider that dangerous.

As for the regeneration issue overall, I should clarify that with the max pack, there are only 2 motors, not 4. And all the technical explanations might make perfect sense (let's be honest...I'm not smart enough to know) but they don't change the fact that regeneration simply doesn't work as well with the Rivian as it has with my other, smaller, EVs. Period. Are there good reasons for that? Sure. But it doesn't change the fact that it's true. Obviously, I've gained a TON by getting the R1T, and I love it overall. I'm very happy I bought it...but the regeneration sucks. It just does.

 

[HyperionMark]

I agree with the blending of the brakes. Yet another example of "please just copy Tesla".

Are we sure it's not more a function of the motors overheating than the battery? Next time this happens please note the temps on each. I know for Tesla's the limitations tend to be at the motors first when regen-ing down hills.

 

[teartags]

So here's one...
On My DUAL version, when it's regenerating, I see the "green bars" (for regen, not blue for accelerate) on the FRONT wheels. Not the rear. Do you quad people see green bars on all 4 wheels?

 

[Dark-Fx]

So here's one...
On My DUAL version, when it's regenerating, I see the "green bars" (for regen, not blue for accelerate) on the FRONT wheels. Not the rear. Do you quad people see green bars on all 4 wheels?

YES we do. Set your traction control to Reduced if you want front and back to regen on the dual.

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