Regeneration Concerns

[Zoidz]

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.

Thanks, interesting experiment. It's something that i will give a try next week, plenty of hills in my immediate vicinity to experiment on.

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[usulio]

My pa always told me never to stand between two guys in a pissing match, but some points:

1) Some more discussion and some data from @jwardell in this thread: https://www.rivianforums.com/forum/threads/r1t-limited-regen-warning-whats-normal.16460/

2) One additional complaint is that the amount of regen limiting is unpredictable too. So not only does regen turn off unexpectedly when you need it, but the level it goes to changes every time.

3) People who have not experienced this going down a steep mountain road should try it or try to imagine it before saying it's not a big deal. And besides that, it's frustrating to be wasting energy with friction brakes.

4) The cause of the limited regen warning is very weird (except for cold battery, that makes sense). jwardell points out: usually acceleration is still not limited. How can the inverters OR the battery OR any other component be overheated if full acceleration is still available?

 

[usulio]

I guess the conclusion from that thread (linked above) is that it's probably about the battery cell chemistry, rather than temperatures directly. The battery isn't overheating, but the chemistry can only accept charge so fast. I don't understand that answer though, because it still limits regen at rates well below fast charging rates. Maybe something about how/where the inverter supplies power versus DCFC.

 

[NorthVan57]

This is a very interesting topic, would love to know the real engineering behind the limited regen, not so sure about the overheating idea, wouldn’t that apply to rapid charging as well?? My Nissan leaf that can’t charge level 3 very well or multiple times on a long road trip can regen down a 6 mile hill at our local ski mountain without any limitation on the regen, very nice as I don’t have to use my friction brakes at all, what if we put rivian on low regen or snow mode? Will the regen duration last longer?? Will have to try that next time I go to the ski hill. has anyone tested how the low regen setting or snow mode acts going down a massive mountain pass slope?

 

[Electrified Outdoors]

First the bolt EV is not a good comparison because max regen is 55kw ... I owned one for 3yrs. Max regen on the Rivian is 150kw. Above 60% Soc your going to hit a wall pretty fast on the R1.

You can try reducing Regen down to normal from high and you may be able to regain more energy. If you want to capture max energy on the downhill you need to start out with less than 60% battery and put it on normal Regen (not high).

As to why they limit it ... Well there is the charge rate... You can't put 150kw into the R1 battery for long at all if your above 60%. Much much shorter if your above 80%. The other is speculation on my part but here goes....

If the inverter heats up too much both acceleration and regen will have to be limited. I suspect Rivian is being proactive to prevent a temperature rise which would limit acceleration along with regen by taking away the regen before a spike occurs.

What you can also try to do is put it in snow mode which will put you in low Regen. In low Regen it won't stop the truck as much but you should be able to put more energy back in since it's Regen at a lower rate.

 

[CrazyOne]

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...

If they do this, there better be a very big and audible warning. I would hate to lose all braking because the brakes overheated. A friend of mine used cruise control on his Audi in mountains and it warped the rotors.

 

[HaveBlue]

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.

The rivian is limited to 220kw because of the supply equipment. Cabinets and cables are limited to 500A and since the battery is roughly 400v, you can do the math. The theorhetical 2C rate would be 250kw-300kw depending on the battery (large or max)

800v only improves the cabinet/cable thermals and gets those cars to 350kw. The motors draw much more current on hard acceleration than a gradual Regen but battery thermals on both sides of the temperature curve limit that over time along with C rate at the top and bottom of the pack. The danger is overvolting random cells at the top or having to large a voltage gap at the bottom since you can't just dump 4.2v into an empty cell.

Then there's the water cooled Bosch motors that might not cool as well as the Enduro oil cooled and overheat during long decel.

Yea Rivian needs a warning before it happens, not as it happens. I've seen a warning even at 80 battery but wasn't going down a hill.

 

[MrMusAddict]

If they do this, there better be a very big and audible warning. I would hate to lose all braking because the brakes overheated. A friend of mine used cruise control on his Audi in mountains and it warped the rotors.

So, imagine a scenario where your following a car down a mountain. Constant blind curves, no passing lane for miles, you're stuck behind this guy. Regenerative braking just became 80% limited (only 20% available).

Your options are;

1. Accelerate into them and crash
2. Ride the brakes manually out of necessity
3. Enable adaptive cruise control, which already blends friction brakes when necessary, and will ride them for you.

The brakes are being ridden no matter what, and if you're in a scenario where regen becomes limited (not just downhill on a mountain pass), you're very likely going to need to apply friction brakes when you need to decelerate.

 

[rhumbliner]

Plenty of people are seeing limited regen when the battery is showing 50 - 60 - 70 degrees.

Are you referencing the ambient air temp or the actual battery temp? Until a few releases ago we had no way of knowing the actual battery temp.

 

[R.I.P.]

Wow. Just wow. Not sure what else to say about some of these posts lol.

Anyway, for those interested in information vs forum combat, this stuff is pretty old news. The inverters are the thermal bottleneck, and they compare quite poorly to the competition when pushed; see the OoS & TFL head-to-head towing tests on the Ike.

The Enduro's inverters are better cooled, don't hit the limits as soon as the Quad's do, but they are still the bottleneck.

 

[CrazyOne]

So, imagine a scenario where your following a car down a mountain. Constant blind curves, no passing lane for miles, you're stuck behind this guy. Regenerative braking just became 80% limited (only 20% available).

Your options are;

1. Accelerate into them and crash
2. Ride the brakes manually out of necessity
3. Enable adaptive cruise control, which already blends friction brakes when necessary, and will ride them for you.

The brakes are being ridden no matter what, and if you're in a scenario where regen becomes limited (not just downhill on a mountain pass), you're very likely going to need to apply friction brakes when you need to decelerate.

That's why the driver is driving the car. All cars have phantom braking and I often press go pedal to get it to move and prevent some one from rear ending me. I know Rivian sees see phantom lanes and steers me out of lane. Most cars will have these problem. If one is not ready to hit brakes in a second, they shouldn't be driving. Car tell that regen is reduced, it can be felt and most importantly we can see that the car ahead is closing.

It's also the reason why it is recommended not to use cruise control in mountains. These should not be a surprise to people who tow large loads or to semi drivers. Cars may get away with them, but will still have warped rotors. Is extreme cases they can burn up the pads. I even know a specific places where this happens. Mild continuous breaking will overheat brakes much more than intermittent harder use. This is because pads don't get a chance to cool down.

 

[Zoidz]

Are you referencing the ambient air temp or the actual battery temp? Until a few releases ago we had no way of knowing the actual battery temp.

Battery temp from the .38 OTA.

 

[KootenayEV]

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.

Tesla doesn't actually blend the brake pedal with regen. They did add a mode where one-pedal driving works more consistently and the car applies friction brakes for you (which appears to be coming in the next OTA). My Leaf actually blended the brake pedal with regen; it wasn't always the smoothest, but it was a much easier car to coast in.

 

[KootenayEV]

My pa always told me never to stand between two guys in a pissing match, but some points:

1) Some more discussion and some data from @jwardell in this thread: https://www.rivianforums.com/forum/threads/r1t-limited-regen-warning-whats-normal.16460/

2) One additional complaint is that the amount of regen limiting is unpredictable too. So not only does regen turn off unexpectedly when you need it, but the level it goes to changes every time.

3) People who have not experienced this going down a steep mountain road should try it or try to imagine it before saying it's not a big deal. And besides that, it's frustrating to be wasting energy with friction brakes.

4) The cause of the limited regen warning is very weird (except for cold battery, that makes sense). jwardell points out: usually acceleration is still not limited. How can the inverters OR the battery OR any other component be overheated if full acceleration is still available?

Thanks for the link to that other thread - excellent info @jwardell dug up and posted over there and in his videos, particularly the second one from 50% (link).

I don't have his technical expertise so can't contribute anything, but did want to say that based on all of my observations over the last few months, this explanation seems the most likely.

On one hand, Rivian is less conservative than my Tesla Model 3 (2018 RWD); at cooler ambient temps with a cold-soaked battery, I'll get more regen out of my R1T than my M3, though not for very long; it fairly quickly reduces. But, I'll often have essentially zero regen in the M3 with a cold-soaked battery, and I haven't experienced that yet in my R1T.

On the other hand though, longer periods of consistent regen reach what appears to be largely a software limitation (likely related to how they infer the cells handle the regen) sooner than my M3 does in ideal conditions.

Having said that, I do still see regen limitations on my M3 sometimes during long mountain pass descents (I have two 1100m descents nearby, one at low speeds around 50-60km/h, and another at highway speeds 100km/h), and I did on my 2014 Leaf before that. The Leaf actually gave you a meter with a few dashes with numerical values - it maxed at 30kW!

Rivian seems to unlock as much regen as they feel comfortable depending on the situation - but it sure would be interesting to know what that is. I think they could choose to improve actual regen amount (not just blend in the brakes like the forthcoming .50 OTA), but they may not in order to provide more battery longevity.

Lastly, I agree with other posters that a warning a few seconds ahead of regen reduction would be helpful.

 

[runningdenver]

I drove up and back to Leadville this week on I-70, my first time using my new R1S in the mountains. A couple of times on long descents, I got a warning that regenerative braking was reduced, and so had to use the regular brake pedal more, but there was always a warning. And it only lasted a few seconds, and then regenerative braking seemed to be back to normal.

Certainly leads to pretty nice efficiency graph. I came down from the tunnel through Idaho Springs averaging 80-85 mph, but was still able to get a 4+ efficiency. Going the other way up the hill was not quite as impressive...

(had to slow down to take the photo)

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