Why is limited regen in cold weather a thing?

[Daniel in SD]

So I got the limited regen warning for the first time the other day (in coastal San Diego!) and I was wondering why they don't just use the regen energy to heat the battery.
I suppose you'd have to run a huge volume of coolant over a 70kW resistive heater to keep it from melting or maybe it's bad for the battery to heat it up too fast.
The lows here are about 45 degrees right now and it takes about 15 miles to get full regen.

 

[ModelNforNerd]

So I got the limited regen warning for the first time the other day (in coastal San Diego!) and I was wondering why they don't just use the regen energy to heat the battery.
I suppose you'd have to run a huge volume of coolant over a 70kW resistive heater to keep it from melting or maybe it's bad for the battery to heat it up too fast.
The lows here are about 45 degrees right now and it takes about 15 miles to get full regen.

Our hearts up North ache for you. What can we do for you, in this, your darkest hour??

 

[Doctor X]

Up here in Canada we loose full regenerative breaking from October to May... we deal with it!

 

[chronopc]

I don't even know if I can tell the difference. I'm getting those dots on a daily basis during these cold months but the car seems to drive the same for me. Range is also similar.

 

[Daniel in SD]

Our hearts up North ache for you. What can we do for you, in this, your darkest hour??

Thanks! We'll be ok. It looks like warmer weather is coming. It should stay above 50 over the next week.

Seriously though it's so simple to convert electricity into heat. I wonder why they don't do it.

 

[ModelNforNerd]

Seriously though it's so simple to convert electricity into heat. I wonder why they don't do it.

Cost.

 

[Daniel in SD]

I don't even know if I can tell the difference. I'm getting those dots on a daily basis during these cold months but the car seems to drive the same for me. Range is also similar.

Yeah it only ends up limiting at high speeds.

 

[M3BlueGeorgia]

Do an extra little charge for your battery just before you leave. That'll warm up the battery and prevent the "limited regen" issue, unless you also charge close to 100%.
It'll also help with range and with acceleration.

But, quite honestly, so long as you have some regen, it's probably not worth the trouble at 45F.
Definitely worthwhile if the car is parked near or below freezing, though.

 

[DdotRoq]

That one moment where having 90 degree weather year-round is a good thing. We had one of our coldest days last week and it was about 70 degrees. Everyone was wearing winter clothing, jackets, sweaters, etc.

South Florida.

 

[strider]

Thanks! We'll be ok. It looks like warmer weather is coming. It should stay above 50 over the next week.

Seriously though it's so simple to convert electricity into heat. I wonder why they don't do it.

Cost and weight. You'd have to drag around an extra heater all the time and still people would complain about not having regen when the battery is full. Plus regen is very peaky - tons of electricity, then zero, then tons of electricity, then zero. Resistive heating elements don't do well with wildly changing power inputs.

They should just automatically blend the brakes so you get the same decel rate until the battery warms up/discharges enough.

But in the meantime, just start your charge later so it's still warm when you leave in the morning.

 

[Daniel in SD]

Just put this under the seat: EcoSmart 36 kW 240-Volt Self-Modulating 6 GPM Electric Tankless Water Heater-ECO 36 - The Home Depot
Make it part of a cold weather package and charge $1k for it. I'm sure people would pay.
To be clear, this is not a problem that affects me personally. I saw the warning for the first time ever and I was wondering why the car is designed that way.

 

[voip-ninja]

Do an extra little charge for your battery just before you leave. That'll warm up the battery and prevent the "limited regen" issue, unless you also charge close to 100%.
It'll also help with range and with acceleration.

But, quite honestly, so long as you have some regen, it's probably not worth the trouble at 45F.
Definitely worthwhile if the car is parked near or below freezing, though.

You might not get the limited regen message on the screen but regen is still going to be limited. I can pre-heat my car for 20-30 minutes while charging it at work when it's 30F outside and the car still has 5 or 6 dots on the regen bar.

For us in mid-west looks like regen will be limited from about October till May, at least in the morning.

Maybe this will motivate me to insulate my garage.

 

[M3BlueGeorgia]

You might not get the limited regen message on the screen but regen is still going to be limited. I can pre-heat my car for 20-30 minutes while charging it at work when it's 30F outside and the car still has 5 or 6 dots on the regen bar.

For us in mid-west looks like regen will be limited from about October till May, at least in the morning.

Maybe this will motivate me to insulate my garage.

As you noticed, and has been discussed many times, heating the interior of the car on the Model 3 doesn't warm the batteries.
Only way to do this, without a heated garage, it to either drive the car a bunch of miles, or charge the car shortly before you leave.

 

[voip-ninja]

As you noticed, and has been discussed many times, heating the interior of the car on the Model 3 doesn't warm the batteries.
Only way to do this, without a heated garage, it to either drive the car a bunch of miles, or charge the car shortly before you leave.

As mentioned in my post the car is plugged in while it's cold and while I am pre-heating it. I actually do the cabin preheat before going out to get it from the office car park and it's still charging when I kick off the climate activation.

 

[SSedan]

In the S and X the battery heater will actually trigger with the interior preheat, since the 3 doesn't have that.....................
Yes they play games with the motor to generate some heat when needed but I suspect this is not as efficient nor effective as a dedicated heater. Warming the battery with either system is not a 5 minute process and it takes a long time for the battery to actually drop to ambient temp, a lot of mass involved.

Try parking outdoors in a windswept area when the high is going to be 0F and then tell us about your regen issues......

Regen is very aggressive recharging I don't know about the other models but my old RWD S regens at up to 60kw, that is half supercharging rate 175miles per hour for my S. Charging alone wont get rid of regen reduction unless done at a high rate for some time. I am unsure if active heating cuts out at half regen or if it warms enough to handle the available charge rate. I do know that if I charge my S at 60amps I can warm the battery enough to have no regen reduction but I don't know if the active warming does it or if the battery naturally getting warm during charging gets it above the half regen limit.

 

[insaneoctane]

Southern California has experienced temperatures that are about 10 degrees below our December average and it's very noticeable- and, yes, we are spoiled. Certainly nothing to complain about relative to other parts of the country, but the difference between never seeing the regenerative limit dash lines and finally seeing them. I have personally been seeing them in the morning for a couple of weeks and my car sits in the garage. My sympathy to the folks with actual cold weather because the limited regen is for the birds!

 

[SSedan]

Here with no prewarm or recent charging Regen can regularly be disabled entirely

 

[TeeEmCee]

Up here in Canada we loose full regenerative breaking from October to May... we deal with it!

The inability to spell “lose” and “braking” is as American as apple pie from Costco ... and now you’re taking even that away from us!

Build the (Northern) Wall!
USA! USA!

 

[ebmcs03]

In Los Angeles just last week. After driving 30 miles i still didn’t get full regen. The battery was like 40%

 

[brucet999]

Thanks! We'll be ok. It looks like warmer weather is coming. It should stay above 50 over the next week.

Seriously though it's so simple to convert electricity into heat. I wonder why they don't do it.

Think about that a little more.
First you would have to get the regen energy captured before it gets to the battery, so there would have to be some sort of high voltage switch placed in the cable between motor and battery with some kind of sophisticated controller that limits heater input to a safe amount of power.
Then there would need to be a heater that can take high voltage, or an additional DC/DC voltage reducer installed in front of the heater.
There would have to be an additional loop in the battery cooling/warming pipes.
That heater would have to somehow operate with non-continuous power supplied at odd intervals.
And where would they find the space for these additional components?

Maybe not "so simple to convert electricity into heat" after all.