R1T Limited Regen Warning: What's normal?

[shap]

I logged going down my hill yesterday, left a room temp garage at 75%, there's a bit of uphill to the road so it's at 73.6% user SOC at the top and only rises to 74.6% after this ten minute downhill drive.
Have a look at all the data, but to me it's just safe software limiting in the BMS, and hopefully Rivian can improve this in the future.

Awesome data, thank you!

So there were several key assumptions:
1. Battery overheating - seems not the case
2. Inverter overheating - based on what you got - probably not
3. Motor overheating - not the case.

Thank you again!

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[Electrified Outdoors]

I logged going down my hill yesterday, left a room temp garage at 75%, there's a bit of uphill to the road so it's at 73.6% user SOC at the top and only rises to 74.6% after this ten minute downhill drive.
Have a look at all the data, but to me it's just safe software limiting in the BMS, and hopefully Rivian can improve this in the future.

Yes, great data there. Would be interested to see the same test at <55% soc. Also, I see the rotor and stator on there...would be cool if we could see the inverter temps.

For the pack...it does start to limit charge rate after reaching 60% soc....so if the same test were run below that, and similar results were obtained, that would seem to lend further evidence to the inverter being the limiting factor in most scenarios.

My understanding is that the inverter is working harder when doing. Regen than it is when providing output to the motors, so it might make sense that it would more quickly generate a lot of heat and cause regen to be limited.

 

[Silver9k]

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 read through 2 pages and didn’t see this response so I figured Id make sure you’re aware that using dynamic cruise control allows the vehicle to blend in the friction brakes. It doesn’t necessarily wait until regen is maxed out and not sufficient. This is probably why you don’t have the issue when using CC.

 

[tcole]

My understanding is that the inverter is working harder when doing. Regen than it is when providing output to the motors, so it might make sense that it would more quickly generate a lot of heat and cause regen to be limited.

In the video @jwardell does call out a number of temperature related things starting about 4 minutes in. Though I don't see inverter temp on there.

I recently watched the Munro Live teardown of the quad motors, and saw that the inverter is shared for each motor pair. It made me wonder if that was the weak link for regen, or at least the thing their conservative software is trying to protect.

 

[Whataboykie!]

Strange, this has never been an issue for me. Maybe it's because Florida is flat!

 

[shap]

In the video @jwardell does call out a number of temperature related things starting about 4 minutes in. Though I don't see inverter temp on there.

I recently watched the Munro Live teardown of the quad motors, and saw that the inverter is shared for each motor pair. It made me wonder if that was the weak link for regen, or at least the thing their conservative software is trying to protect.

That is what Kyle was talking about when he was speaking about the REGEN issue. His point was that it may be that inverters reach their thermal max and then REGEN will be limited.

From what I see in the video, it is not 100% clear, but it may be that inverters are not the only ones to blame - aka there is a software limitation as well. Maybe software tries to prevent inverters to overheat based not on actual temperature but the amount of power per minute for REGEN...

 

[jwardell]

Put it this way, it's not motor or inverter temperatures, or your acceleration would be limited as well. If the inverter were too hot, it's generating heat no matter which way it's generating torque so both your regen and acceleration would have the same 70A limit, and that is most definitely not the case. At any time when regen is limited down to 70A, you can still punch it and pull 1800A.
Likewise the pack is massive and take a huge amount of time and energy to change in temperature..the pack temp is almost a flat line here.

I will definitely repeat the test around 50% SOC.
But at any time you can just look at that BMS charge current limit to know what you can regen to. Maybe I'll add that to one of my dash screens. But the question isn't so much that limit number, but how long you have till it is significantly reduced.

I have some other logs, and can look at that BMS charge limit (which seems to only apply when driving) and can look at various SOCs:
90% - 265A
80% - 300A
70% - 400A
60% - 475A
50% - 520A
40% - 570A
30% - 575A
...that said, regen is limited to a much lower current, maybe 325A max.
There are lots of performance items in an EV that have TONS of limits that define them. It's why I try to find the data to help understand how things work in various situations.

 

[Electrified Outdoors]

Put it this way, it's not motor or inverter temperatures, or your acceleration would be limited as well. If the inverter were too hot, it's generating heat no matter which way it's generating torque so both your regen and acceleration would have the same 70A limit, and that is most definitely not the case. At any time when regen is limited down to 70A, you can still punch it and pull 1800A.
Likewise the pack is massive and take a huge amount of time and energy to change in temperature..the pack temp is almost a flat line here.

I will definitely repeat the test around 50% SOC.
But at any time you can just look at that BMS charge current limit to know what you can regen to. Maybe I'll add that to one of my dash screens. But the question isn't so much that limit number, but how long you have till it is significantly reduced.

I have some other logs, and can look at that BMS charge limit (which seems to only apply when driving) and can look at various SOCs:
90% - 265A
80% - 300A
70% - 400A
60% - 475A
50% - 520A
40% - 570A
30% - 575A
...that said, regen is limited to a much lower current, maybe 325A max.
There are lots of performance items in an EV that have TONS of limits that define them. It's why I try to find the data to help understand how things work in various situations.

This is awesome info. I think its great all the work your doing for the Rivian community. I used scanmytesla quite a bit. I know with Tesla power output was limited but didn't necessarily show the end user anything to indicate such.

The scanmytesla would show available power in kw which of course indicated the amount of power you were able to pull out of the battery at that time. Do you think Rivian has any such signal available on the CAN? The inverter may have limitations when its acting as a rectifier vs a converter?

I think your correct that there are a lot of different limitations and the Rivian engineers have to account for all of them while also making sure there are no drivability issues with the truck. With that said its likely there are multiple limiting factors at play here.

 

[usulio]

One Q, jwardell: it looks like you got battery pack temp, rotor temp, and stator temp (some of those possibly estimated), but you don't have access to inverter temps, right?

 

[jwardell]

Sorry for the delay, here is new data, taken at 50% SOC. As you can see you get a few more seconds before it derates, but more significantly it seems to derate to 200A instead of 75A limit. Similar to when you're DC charging.
I also included IGBT temps, which stay reasonable. Again if motors or inverters were overheating, you would be limited on acceleration just as much as regen.
I also switched between High, Standard, and Low regen and showed they do in fact each have maximum sustained regen power. That's an easy test you can do and feel yourself.

 

[shap]

Thank you @jwardell! Very useful data, that clarifies many assumptions

 

[Electrified Outdoors]

Sorry for the delay, here is new data, taken at 50% SOC. As you can see you get a few more seconds before it derates, but more significantly it seems to derate to 200A instead of 75A limit. Similar to when you're DC charging.
I also included IGBT temps, which stay reasonable. Again if motors or inverters were overheating, you would be limited on acceleration just as much as regen.
I also switched between High, Standard, and Low regen and showed they do in fact each have maximum sustained regen power. That's an easy test you can do and feel yourself.

Great data here! In looking at what I said ...sometimes what I say doesn't come out right.

So it looks like it's related to soc. To put this a different way on the inverter, is it possible Rivian is limiting Regen also for the very reason you mention (before temps reach a certain threshold)? My thoughts is Rivian doesn't want temps to rise and have to reduce acceleration/Regen...something driver's complained about with Ford products. My line of thinking was that by limiting Regen more they prevent higher temps which would result in both reduced Regen and reduced acceleration as you correctly point out.

Better to limit one then to limit them both right? Maybe also part of their thermal management strategy? Many drivers would see reduced acceleration/torque as a drivability issue.

 

[Dark-Fx]

I'm guessing the regen limitations are related to cell specifications rather than any temperature limitation. Should be verifiably different with the max pack battery if that's the case.

 

[jwardell]

I'm guessing the regen limitations are related to cell specifications rather than any temperature limitation. Should be verifiably different with the max pack battery if that's the case.

This is the point. It's charge rating of the cells and chemistry. Most have a much higher C rating for discharge than charge. It's got nothing to do with temperature at normal temps. Rivian is just playing it safe and trying to track and limit how quickly energy goes into the cells, and is more restrictive the closer you are to the top. With a tesla, it needs to be over 90% SOC before you see any limitation but Rivian limits much lower. The next experiment is how it is given back...as you can see I do have some positive pulses that do not bring back the regen right away, but I do know once I get out to the flat road it does come back quickly with less than a minute of break. I'll have to think of some way to test and classify that.

 

[usulio]

This is the point. It's charge rating of the cells and chemistry. Most have a much higher C rating for discharge than charge. It's got nothing to do with temperature at normal temps. Rivian is just playing it safe and trying to track and limit how quickly energy goes into the cells, and is more restrictive the closer you are to the top.

Hmm. What voltage comes out of the inverter? For example, 200A at 240V would be 48kW, a lot less than a fast charger. Or is it only amperage that matters here?
Edit: I see you discuss kW in the video, but curious where those kW numbers come from. And I still wonder why Rivian would limit regen kW to much less than DC fast charge kW...

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