Is this how regen is supposed to work?

[(crunch)]

I've had a MY for a couple of weeks now, and took it on a trip to a snow mountain yesterday. Regen on the way down various mountains/hills didn't quite work how I was expecting.

On the drive to the snow mountain, I got about halfway there and started up a different mountain (or at least a large hill). I’d been driving a good hour so I assume the battery wasn’t cold, and I was probably on about 80% battery. On the way down the other side I was using regen a lot obviously and it started to give me the dots and the limited icon. I didn't think too much of that at the time, but in retrospect I'm not sure why it was limiting me.

Then on leaving the snow mountain at the end of the day, I guess the battery was coldish (though it was about 8C outside so no colder than a typical morning here lately), but the limited regen really only started after I’d been going downhill and using it a lot, maybe 10 mins into the drive (it wasn't limited at all when I set off). The more I used regen, the more dots i got and the less I could use it. After I’d levelled out and driven a bit, I got the full regen bar back but again it started shrinking the more I used it on the next downhill stretch. I had to use the actual brakes (which weren't great I must admit) for most of the way down.

Is that how it's supposed to work? I understand it'll be limited if the battery is cold, and I'd perhaps put the second part of the above (leaving the mountain at the end of the day) down to that, but then I'm not sure why it also limited me when going down the first mountain after I'd been driving a good hour or so.

 

[GtiMart]

It's not an on/off flag with the battery temperature. What you describe makes sense to me based on my experience. When the battery is a bit cold it will still accept high regen but the "max regen" value will slowly go down as you regen. If you go down a long hill eventually you'll feel the reduction. As you accelerate afterwards the max regen value will creep back up. (as seen in ScanMyTesla).
Said another way, the car accepts more power in regen than it would accept if you plugged at a supercharger for a given battery temperature, but only for a short time. It's all about protecting the battery for longevity. Regen can go as high as 65kW or even more.

Cars with a heat pump (2021 and later) can scavenge heat from the battery to heat the cabin. It's very efficient but it means your battery will not necessarily be very warm even after one hour of driving.

 

[ewoodrick]

Regen amount is based on temperature and battery state of charge (SoC). If temp is low or state or SoC is high, regen will probably get limited. If they are both at their extremes, it will get limited.

So 80% battery and cold temps and you will have limited regen.

At 8C, at 50 mph, the battery isn't going to get a lot of change to warm up. That's why Tesla now has the precondition capability before departure.

You'll also be seeing about 30% degradation on range right now, that happens when the temps get cold. You'll get them back when spring rolls around.

 

[(crunch)]

Fair enough, thanks to you both. As long as it’s normal then that’s fine

 

[dafish]

Well you can color me surprised. 46f, about what 8c is, ain’t what I’d call cold.

 

[ewoodrick]

Well you can color me surprised. 46f, about what 8c is, ain’t what I’d call cold.

It's below 65 isn't it? That battery is going to start to get cold and not able to deliver all of it's energy.

 

[archae86]

Regen amount is based on temperature and battery state of charge (SoC). If temp is low or state or SoC is high, regen will probably get limited. If they are both at their extremes, it will get limited.

In addition to those two things, currently available regen max is heavily affected by recent power flow.

I get to watch this on Scan My Tesla, helped by the fact I have a steady 1000 foot descent over about 4 miles distance in one of my regular paths.

On my model 3, the ultimate max regen is 85 kW. But if I am starting with a pretty high SoC and not high battery temperature, Max right at the start can easily be 65. That means every slight change shows.

Use of regen steadily lowers the max available. Going down my 1000 feet can easily lower max from 65 down to 15 or 20 WITHOUT sufficient change in battery cell temperature of SoC to explain more than a tiny part of the reduction. And 15 or 20 is NOT enough to stop at a stoplight on that hill with standard deceleration without friction braking (65 is enough).

While just waiting gives a slow recovery of regen-impaired level, use of propulsion power gives rapid recovery. Just accelerating from a stoplight to 55 mph cruise gives a substantial recovery in available max regen.

Too few of our frequent contributors here live with substantial elevation change for the impact on regen max of recent power flow to get discussed frequently.

 

[GtiMart]

That is what I was saying higher up, thanks for backing that up with your experience.

 

[ewoodrick]

In addition to those two things, currently available regen max is heavily affected by recent power flow.

I get to watch this on Scan My Tesla, helped by the fact I have a steady 1000 foot descent over about 4 miles distance in one of my regular paths.

On my model 3, the ultimate max regen is 85 kW. But if I am starting with a pretty high SoC and not high battery temperature, Max right at the start can easily be 65. That means every slight change shows.

Use of regen steadily lowers the max available. Going down my 1000 feet can easily lower max from 65 down to 15 or 20 WITHOUT sufficient change in battery cell temperature of SoC to explain more than a tiny part of the reduction. And 15 or 20 is NOT enough to stop at a stoplight on that hill with standard deceleration without friction braking (65 is enough).

While just waiting gives a slow recovery of regen-impaired level, use of propulsion power gives rapid recovery. Just accelerating from a stoplight to 55 mph cruise gives a substantial recovery in available max regen.

Too few of our frequent contributors here live with substantial elevation change for the impact on regen max of recent power flow to get discussed frequently.

I've got a hill near me that's 4000 ft up and 4000 ft down. It takes about 20 minutes to climb and 20 minutes to decend.

It's fun watching the energy gauge going to -999 for over 15 minutes and then +999 for over 15 minutes.