Downhill regen limiting -- capacity, temperature, etc.

[bxr140]

(mod note: separate topic split from the Multi-gear EVs are probably the future thread)

Since you can set the slider in 1% charge increments, you should be able to set it to something eg. 96% that allows you to capture all or most of the regen on the way down.

Unfortunately, it doesnt exactly work that way. If you immediately start a long descent you'll get regen limiting regardless of starting SOC. Cooler temps seem to result in regen limiting kicking in soone so i think its a thermal thing triggering the limiting, but that's just a guess.

Somewhat related, any soc higher than 90% limits my regen even though I don't get the yellow line.

 

[ggr]

Unfortunately, it doesnt exactly work that way. If you immediately start a long descent you'll get regen limiting regardless of starting SOC. Cooler temps seem to result in regen limiting kicking in soone so i think its a thermal thing triggering the limiting, but that's just a guess.

Somewhat related, any soc higher than 90% limits my regen even though I don't get the yellow line.

Yes, there are also thermal limits to regeneration, and I guess it gets cold on a mountain top. But if you're prepared to pre-heat the bottom of the car, as people do with airplane engines in cold climates, maybe you could get around this. A cheapo 1kW radiant heater under the car, timed to turn on an hour before you leave?

 

[bxr140]

Yes, there are also thermal limits to regeneration, and I guess it gets cold on a mountain top. But if you're prepared to pre-heat the bottom of the car, as people do with airplane engines in cold climates, maybe you could get around this. A cheapo 1kW radiant heater under the car, timed to turn on an hour before you leave?

To be clear, I'm not talking about extreme weather here. I live at 1500 ft in the Bay Area. Extreme cold is low 40s or (GASP!) high 30s. Today, for instance, my car was cold soaked at 66 deg in my garage, and on the way down the hill I saw a low of 49 deg. My regen limiting kicked in at -0.4kwh today, which is pretty typical unless its really cold (when it kicks in more around -0.2kwh). Summer mornings I can sometimes get to -0.5 or -0.6 before limiting, but only if its really hot or I had recently been driving can I make it down my hill without any regen limiting.

From today:

 

[Saghost]

To be clear, I'm not talking about extreme weather here. I live at 1500 ft in the Bay Area. Extreme cold is low 40s or (GASP!) high 30s. Today, for instance, my car was cold soaked at 66 deg in my garage, and on the way down the hill I saw a low of 49 deg. My regen limiting kicked in at -0.4kwh today, which is pretty typical unless its really cold (when it kicks in more around -0.2kwh). Summer mornings I can sometimes get to -0.5 or -0.6 before limiting, but only if its really hot or I had recently been driving can I make it down my hill without any regen limiting.

From today:
View attachment 79053

Have you tried changing the charge limit?

I suspect the regen limiting has a lot more to do with the total battery state of charge than it does the distance above the last wall charge. Assuming it won't be a problem for your commute, try charging to 80% instead (or 70%) and see if the limiting still occurs.

 

[ggr]

Have you tried changing the charge limit?

I suspect the regen limiting has a lot more to do with the total battery state of charge than it does the distance above the last wall charge. Assuming it won't be a problem for your commute, try charging to 80% instead (or 70%) and see if the limiting still occurs.

As you can see from the pic, he's already nowhere near full. At this point I'm at a loss to explain it, unless the fairly significant regen is actually overheating the battery. Does the air conditioner come on? That would be a clue. On the roadster I can look at the temperatures, but I don't think you can do that on the Model S without enabling the debug mode.

 

[JRP3]

I would think regen level to SOC ratio should be similar to the supercharger level to SOC ratios.

 

[brianman]

Since you can set the slider in 1% charge increments, you should be able to set it to something eg. 96% that allows you to capture all or most of the regen on the way down. I can't understand how they would not be able to figure this out on the spot.

The settings for charging are [50,90]% (in 1% increments) and [100]. There is no ability to set values in the (90, 100) range IIRC.

 

[green1]

I would think regen level to SOC ratio should be similar to the supercharger level to SOC ratios.

Not a good idea, tapering while charging is ok, tapering while driving would lead to horribly unpredictable braking, I want my pedal inputs to always have a predictable result.
Tesla's current setup where they chose a middle of the taper curve 60kW makes mores sense than having it 120kW when you're almost empty and 5kW when you're closer to full, you would never know what to expect when you lift off the pedal. The only way they could improve it right now would be to find a way to bleed off that 60kW somewhere when the pack is too cold or too full to accept it so as to maintain that regen at a predictable level in the few cases they haven't already (when the pack is too cold, I think 60kW of heat would be a good place to send it...)

 

[Saghost]

As you can see from the pic, he's already nowhere near full. At this point I'm at a loss to explain it, unless the fairly significant regen is actually overheating the battery. Does the air conditioner come on? That would be a clue. On the roadster I can look at the temperatures, but I don't think you can do that on the Model S without enabling the debug mode.

I would think regen level to SOC ratio should be similar to the supercharger level to SOC ratios.

My thinking was along the same lines as JRP3's. If you look here, Bjorn crossed the 60 kW threshold at something like 60% charged at about 3:05 into the video and ~245 kilometers rated? (I think - though some early videos he used ideal) range - the earlier post looks to be somewhere over 80%, much higher.

(At ~80% in the video, somewhere around the 5 minute mark, the Supercharger is down under 40 kW - not much more than the limit shown in the picture.)
Walter

 

[bxr140]

Have you tried changing the charge limit?

Yup. I've left my house charged to everything from 50-100% SOC, and not-charged (as in, it sat overnight not plugged in) to everything between 20 and 80% SOC. I've reset the charge limit to a higher level after unplugging in the morning, and I've pre-heated the car (I never use range mode). I get limiting in basically every situation, and the only real pattern I see is that cooler weather makes the regen limiting kick in sooner. Again, only if it's hot out or the car has been operated recently (and so presumably is at "operating temp", whatever that means) can I make it down my hill without triggering the regen limiting.

 

[Saghost]

Yup. I've left my house charged to everything from 50-100% SOC, and not-charged (as in, it sat overnight not plugged in) to everything between 20 and 80% SOC. I've reset the charge limit to a higher level after unplugging in the morning, and I've pre-heated the car (I never use range mode). I get limiting in basically every situation, and the only real pattern I see is that cooler weather makes the regen limiting kick in sooner. Again, only if it's hot out or the car has been operated recently (and so presumably is at "operating temp", whatever that means) can I make it down my hill without triggering the regen limiting.

That's interesting - and very much not what I would have expected from what little I know of the physics involved. Hopefully someone else can shed some light on it.
Walter

 

[JRP3]

Not a good idea, tapering while charging is ok, tapering while driving would lead to horribly unpredictable braking, I want my pedal inputs to always have a predictable result.
Tesla's current setup where they chose a middle of the taper curve 60kW makes mores sense than having it 120kW when you're almost empty and 5kW when you're closer to full, you would never know what to expect when you lift off the pedal.

I should have been clearer, I meant the taper starting from the current 60kW level.