Regeneration Concerns

[mtberman]

There is so much BS in this thread. If you don’t know why regen is limited, please do not post your theories.

Fact: The regen is limited to a ridiculous degree because the Rivian inverter overheats because it has a poorly designed cooling system. That’s it. That’s the problem. It’s not the battery and it’s not anything else.

My Audi e-tron uses zero friction brakes on the descent into Denver, be it on on I-70 or on Hwy 285. It returns massive amounts of electricity back into the battery and its thermal management system pulls heat out of the inverter as needed to avoid the sort of nonsense that happens with Rivians. Our Bolt behaves similarly. Because GM and Audi tested their car to ensure consistent, repeatable performance.

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[Zoidz]

Here’s the previous thread: Regen Disabled .

I disagree with the “blended brake” approach. I’d rather they fix their battery management system. As @Cosmacelf pointed out, having a single cooling plate just doesn’t cut it.

I'm not convinced that the person at Rivian knew exactly what caused it and just used "overheating" as a generalization. Plenty of people are seeing limited regen when the battery is showing 50 - 60 - 70 degrees. Clearly the battery is not overheating - they are limiting regen for other reasons, one of which could be so they do not exceed the safe charge rate, inverter heating, etc.

 

[Zoidz]

There is so much BS in this thread. If you don’t know why regen is limited, please do not post your theories.

Fact: The regen is limited to a ridiculous degree because the Rivian inverter overheats because it has a poorly designed cooling system. That’s it. That’s the problem. It’s not the battery and it’s not anything else.

My Audi e-tron uses zero friction brakes on the descent into Denver, be it on on I-70 or on Hwy 285. It returns massive amounts of electricity back into the battery and its thermal management system pulls heat out of the inverter as needed to avoid the sort of nonsense that happens with Rivians. Our Bolt behaves similarly. Because GM and Audi tested their car to ensure consistent, repeatable performance.

You tell everyone to not post theories. And then you post a "fact" that it is strictly due to the inverter overheating (which it may be) and nothing else. You apparently have evidence to prove that fact? Please share it. Otherwise, yours is just a theory too.

 

[jackson4w]

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.

as someone getting ready to take delivery on blue r1s with a similar commute (1000 feet over two miles down driveway) any tips for that? Do I charge to a lower level overnight? Approach the drive down in any particular setting or way?
Thanks for any advice!

 

[Zoidz]

as someone getting ready to take delivery on blue r1s with a similar commute (1000 feet over two miles down driveway) any tips for that? Do I charge to a lower level overnight? Approach the drive down in any particular setting or way?
Thanks for any advice!

I don't do anything different at all. It's just in the back of my mind that regen might be lower so I am ready for it if it happens. I think this reduced regen affects people to varying degrees. It does not bother me at all.... ?‍

 

[Opiate]

I make the same drive in my R1t its just like yours My tesla didnt do that It’s annoying as hell. Hope riv fixes it.

 

[teartags]

When I'm on my way down out of the mountains, I switch to regular regen (instead of high). Seems like it "lasts" longer and when it changes, it's not as abrupt.

 

[Thedude]

I can't tell if this is being sarcastic with the assumption that the gauge already gives this.

Or if this post is about wanting a better gauge.

Sarcastic since the gauge already exists with all that information.

 

[mtberman]

You tell everyone to not post theories. And then you post a "fact" that it is strictly due to the inverter overheating (which it may be) and nothing else. You apparently have evidence to prove that fact? Please share it. Otherwise, yours is just a theory too.

Do an internet search. If you can’t find it quickly look for the term Rapidgate. There are some videos that are worth watching.

The problem can be reproduced as follows: Find a steep uphill grade and accelerate up it. The rapid discharge will heat up the inverter. Next, descend a very steep hill. The regeneration similarly heats the inverter and the limit will kick in within a few miles.

 

[s4wrxttcs]

Sarcastic since the gauge already exists with all that information.

That was my initial reaction.

The issue I have with the gauge is it doesn't always tell you ahead of time. What good is a gauge if it only partially works?

As an example there is moderate hill that I go down on the way to work. Before the hill the gauge doesn't show any significant loss of regen. But, then suddenly going down the hill will trigger the gauge to change and the limited regen notification to come up. It doesn't always do this, but some of the time it will.

The gauge does seem to be fine for State of Charge limitations, and low battery temp limitations. The gauge can't do much to solve the bigger problem of the regen capability being really limited.

I can agree to disagree with Rivian on limiting regen to such a low SOC. I think it should not even begin to limit it at 90%, but Rivian has it around 85% or less.

I can completely understand limiting regen with cold battery temps. Now I do think Rivian is being way more conservative then the Tesla's I had previously, but again its their choice.

But, there seems to be something more problematic going on which is limiting regen on the fly. Either something is getting too hot or there is some bug.

 

[Oldsmobile_Mike]

I've had my Rivian since March and never seen any issues or alerts with Regen. Maaaybe one time when I charged to 100% as a test, but that's to be expected. Then again, I live on flat terrain and spend most of my life sitting in traffic. Not driving down any mountains in Northern Virginia / DC area traffic. ?

 

[VSG]

Separately, I don't see how the number or power of the motors would make a difference. If the same mass vehicle is changing speed at the same rate, I would think the energy to the battery is the same no matter how many motors are sharing the task of converting kinetic energy to potential energy.

Yes, but that's not the issue - the question is where the limitation kicks in. The number of motors and the power of the motors tells you the maximum amount of energy that can be produced, and as long as that maximum is less than the battery can accept, there will be no limitation.

Let's say just for the sake of an argument that 1 motor can produce 50kW when braking. Then 4 motors can produce 200kW. Since 50kW is well within the battery pack's capacity over most of the charging curve, you will rarely if ever see regen limited when only braking with one motor. But when braking harder, 4 motors can generate up to 4 times as much energy as 1 motor, and a Rivian can only take that much energy over a fraction of the charging curve. Likewise with the power of the motors. If you had 4 motors that could only generate 10kW each, then you would again rarely see a limitation because the battery pack can take more than that over most of the charging curve.

 

[VSG]

There is so much BS in this thread. If you don’t know why regen is limited, please do not post your theories.

Fact: The regen is limited to a ridiculous degree because the Rivian inverter overheats because it has a poorly designed cooling system. That’s it. That’s the problem. It’s not the battery and it’s not anything else

I guess you're talking about me, even though you don't say what you think is BS. So let me ask you this: What is it I said that is BS?

You happen to believe that the regen limitation is entirely due to the inverter temperature. OK, but wouldn't you say the same about the Rivian's charging curve - that it's limited by the inverter temperature? And isn't that EXACTLY what I'm saying? That is, the charging curve reflects how much energy can be put back into the pack at any given time/condition. It doesn't matter if that energy is coming from a DCFC or from the motor regeneration. Whatever is limiting the charge rate (which DOES include the inverter temperature) will also limit the regen. So if you "fix" the cooling, then that will improve regen AND it will improve the charging curve.

But you're clearly wrong about the inverter temperature being the only thing that limits regen. State of Charge limits charge rate at higher SoC when the inverter isn't stressed at all, for example. It's not just one thing, nor did I claim any one thing was the main cause.

The only claim I made is that the regen energy is going into the battery, and the amount you can put into the battery at a specific time and under specific conditions is called the charging curve.

If you heat up the inverters with your so-called "rapidgate" maneuver, then try to immediatly DCFC, you will see your charge rate is reduced, just like the regen is reduced if you heat up the inverters. 100% consistent with what I said.

And as for your Audi example, that only has a fraction of the Rivian's horsepower and the etron has a charging curve that is almost 150kW until about 75%. That means it can generate less than 1/2 the regen power as the Rivian and yet can charge at 3/4 of the Rivians rate and over a greater range of SoC. That means the Audi has at least 50% more headroom than the Rivian and has that headroom over a greater range of SoC. So yes, it's obvious the Audi will be far less likely to hit the limitation in regen. This is 100% consistent with everything I've been saying.

You can't avoid physics - if you're generating energy through regenerative braking it has to go somewhere. If your battery pack can't accept that energy due to temperature, SoC, inverter limitations, etc, you can't just drop electrons all over the road. Instead, you have to stop generating energy - i.e. limit regen.

 

[mtberman]

I wasn't referring to anyone specific but my gosh that’s a lot of words. All to say the inverter overheats.

The point: No legacy carmaker has put out a higher end EV that overheats on mountainous downhill grades in this manner. This flaw is a real miss for Rivian.

 

[VSG]

Maybe *you* could use your words - grunts aren't especially useful over the internet. If you think the Rivian is "overheating" all the time you're not paying attention. I'm not inclined to use smaller words or fewer words just to convince you.

220kW max charging for a 400V vehicle is not bad at all. Most others can't reach that high, including your Audi, because they have some limitations somewhere in their charging system. If the Rivian cooling system is "poorly designed" that would indicate your Audi charging system is also poorly designed, because Rivian bests it significantly over the first 40-50% of the charge curve.

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