JonMu
Member
All by regen issues (Regenerative braking temporarily reduced) were with the battery near 50%...
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Regen Braking Temporarily Reduced - Every time
- Thread starter HeyEph
- Start date
Srad600Volt
Member
Interesting, I wasn’t even aware of the bubbles until reading this thread. Today on a drive, during a long downhill section I noticed the bubbles for the first time in my car. Five of them that later went to four before disappearing, BUT ambient temps were in the low 70’s, SOC was around 61% and I’d been driving for over an hour?
The BMS is quite complicated and there's no easy answer as to what conditions are needed and how many bubbles there are to limit the brake regen. Originally I thought it was based upon just the battery temperature, but it's not. I've been monitoring my battery temps in the morning via the SMT app and I've seen certain temps at different driving times and the brake regen levels are different.
I've left my home with the battery packs at 70F after pre-charging and then driving for 30 minutes to see a 4F rise to 74F. The brake regen is completely removed at 72F.
I've also left my home without pre-conditioning and the battery pack at 54F. 75% brake regen is limited. After 80 minutes of driving, battery packs are 74F and there's still ~ 6 bubbles. There are other conditions that the BMS is taking into account and I haven't been able to figure out what those are, but it's not strictly the battery temps.
Also, each quarter section on the left of the power bar is about 25 kW, so if the system restricts brake regen to 1/2, you can max brake regen 50 kW. When I had the system at 75%, the most I would get is 24.xx kW of brake regen. When it was at 50%, I was getting 49.xx kW of brake regen.
The key thing, I've found, is pre-conditioning whenever possible, especially if you're plugged in at home and leaving. The brake regen limitations are completely removed or very minimal every time I've pre-charged to warm the batteries up.
TomServo
Active Member
I too have just noticed the "dots" on the right side of the power bar. My car was charged to 80% on a 40amp lvl 2 EVSE, the temp in my garage when I left home was 63 degrees, OAT was 45 degrees and SUNNY, drove 10 miles and when I got to my destination the "dots" were still visible. I parked for 30 minutes in the bright SUN and drove home. I did some UBER hard acceleration pulls followed by max regen to a full stop a few times and when I pulled into my garage after the same 10 miles all the "dots" were still present. This was the first time I have experienced this.
We have some sunny days getting bak int the 70's this week and will keep an eye on this.
We have some sunny days getting bak int the 70's this week and will keep an eye on this.
Get used to it 
As others have said, the pack is happy only over ~72F. Even if it's 60-70F outside, if it was 40F during the night the pack is at 40F and will take hours to ramp up if you're just driving. It helps to charge the car as the car will heat the battery first. Leaving the battery at lower charge has been reported as helping somewhat by some people but you won't get it all back.
Don't look at the dots for a precise value, it's a relative indicator. Even when there are no dots, you sometimes have less than the maximum 85kW of regen. You just don't get a message. In real cold you also lose power and can get dots on the right side... It'S just the BMS protecting the battery, don't worry.
As others have said, the pack is happy only over ~72F. Even if it's 60-70F outside, if it was 40F during the night the pack is at 40F and will take hours to ramp up if you're just driving. It helps to charge the car as the car will heat the battery first. Leaving the battery at lower charge has been reported as helping somewhat by some people but you won't get it all back. Don't look at the dots for a precise value, it's a relative indicator. Even when there are no dots, you sometimes have less than the maximum 85kW of regen. You just don't get a message. In real cold you also lose power and can get dots on the right side... It'S just the BMS protecting the battery, don't worry.
krcossin
Member
Thanks for posting and replying everyone, I started thinking the reduction in regen was a result of an OTA update. But it is true the season has changed and my Michigan overnight temperatures have dropped below 40°
Srad600Volt
Member
But that's the interesting bit. In the first part of my drive (going up the mountain) regen was performing at 100% (indicated on the bar). While I was driving in the canyons, regen was still at 100%. The bubbles only appeared when I was heading home (down the mountain) and had sustained periods of regen. In this case, this makes me doubt it was a low temperature issue, since the pack temps were good for most of my drive. Maybe it was an overheating issue? Is there such a thing as too much regen, even when SOC is low?
The BMS will also limit brake regen if you're going back down the mountain due to the heat generated.
Using ScanMyTesla I can see the "max regen" value change while driving. After using some regen, the max value lowers for a bit before coming back. It's like the pack doesn't want to charge at high rates too often. You know, 85kW is ~supercharger territory. If you're going mostly downhill, then engines are not producing much heat I guess. It's their heat that's circulated in the battery. If it's cold outside, the battery could technically get colder while driving although with regen you're charging it which generates some heat. Ultimately, what we need to remember is that the BMS is doing its job protecting the battery.
Srad600Volt
Member
That rings true to me. I'm betting there was so much regen, that things got too hot. Which is a bummer because I was starting to recoup most of my output until this kicked in. At one point I was at 189 miles to empty, after almost 13 miles later, I was showing 192 miles to empty. It'd be fun to be able to charge the car up by driving down a mountain!
JonMu
Member
I'll bite, how does one activate pre-conditioning? I thought user activated pre-conditioning was kinda a myth. The BMS does it's magic and none of the magic include user intervention (like pre-conditioning).
Just turn on the HVAC. In colder weather, Stator motors will warm up and coolant will pass thrift then and eventually pass through batteries.
You can also set a Tesla supercharger as a navigation destination and the batteries will warm up.
This is why you'll see Model 3 owners, in the winter, lose miles/ battery percent while plugged into a 110v charger. The pre-conditioning process takes more energy than what the electrical outlet can provide.
@HeyEph, I ran into a similar issue and had a SC appointment to look at it. They ended up replacing the Battery System Control Unit.
Essentially I was getting the Regen dialogue non stop once the temperatures got colder. At one point my regen was weak sauce and never got any stronger as the drive progressed. The regen performance degradation and dialogues were pretty consistent and constant.
All is good after the fix!
Essentially I was getting the Regen dialogue non stop once the temperatures got colder. At one point my regen was weak sauce and never got any stronger as the drive progressed. The regen performance degradation and dialogues were pretty consistent and constant.
All is good after the fix!
What was the battery percentage and outside temperature when you started down the hill? And what was the battery percentage and outside temperature when you got the regen limited message? Assuming that long of a downhill trip meant an increase in outside temperatures which might factor into cooling.
Since regen did work at the start, we can assume that battery temperature was adequate and battery level was low enough to accept charging from regen. So if regen did work and then went away over time, that's probably because:
- the battery temperature changed to something too cold or too hot for accepting that much charge, so BMS reduced regen, and/or
- the battery charge level was too high to accept that much current, so BMS reduced regen, and/or
- it was a thermal issue and cooling of the motors was needed after a prolonged regen period.
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