Battery warming speed

[abasile]

I park outside and today it's -4.6 C. All I do is insure the charge stops close to when I'm ready to leave, and preheat the car for two or three 15 minute cycles with range mode off. This will allow close to 30 kW of regen (about 50% or maximum) for the first few miles on more or less level ground. If you were going downhill, the regen would warm the battery up even faster than it does for me as the motor would be creating heat. If I lived where you did, I'd probably still have to use the friction brakes a bit, but not that much.

This is good to know.

However, if it's below freezing, the car was already charged 24 hours prior, and you just get in the car and start driving, how much regen do you typically see? How long before the regen reaches a "reasonable" level?

I ask because our family routines vary considerably, I don't have a regular commute, and I can't expect other family members to do a lot of prep work to warm up the battery before driving. I think they'll be willing to preheat the car for 15-30 minutes from the app, though not necessary on "shore" power. I know from LEAF experience that timing the end of charging to coincide with departure is good to do, but that's been sort of hit and miss for us. So we end up charging to 80% whether we need to or not, and the car sits at that level of charge until it gets used at some point each day or maybe not until the next day.

 

[jerry33]

However, if it's below freezing, the car was already charged 24 hours prior, and you just get in the car and start driving, how much regen do you typically see? How long before the regen reaches a "reasonable" level?

This is a kind of "it depends" and YMMV question. There are several possibilities:

1. Range mode is off and you can preheat the car (usually that's not a problem as everyone wants to get in a warm car). If you do this and switch to range mode on when driving, it takes about ten miles before the line is totally gone. The yellow bar will be at about 30 or between 30 and 60 when you start. I've found for most urban and suburban driving, once the bar is at about 30 kW, it really feels like you have full regen. You would notice the difference going 50 mph (80 km/h) or faster.

2. Range mode is off and you can preheat the car, and you start driving with range mode off. This will heat the battery quicker. I don't do this as a rule, so I don't know the exact time.

3. Range mode on (because I forgot to turn it off when I parked) and you can preheat the car, and you start driving with range mode on. In this case you'll start with the yellow lines at about 15 kW. Driving takes about ten miles to move the bar to 30 kW.

4. Range mode on and you can preheat the car, and you start driving with range mode off. This will be faster than #3, but it's not something I generally do.

5. No preheating. You start out with zero regen. I don't have a good value for this one.

The colder it gets, the longer it will take. I've heard that you need 6-8 15 minute cycles if it's -20.

I'd strongly recommend leaving the car plugged in every time you park at home--especially in cold weather. It's fine for it to stay plugged in for days.

 

[abasile]

This is a kind of "it depends" and YMMV question. There are several possibilities ...

Thank you so much for the detailed response. This puts my mind at ease regarding the regen. As long as the regen is in the 15-30 kW range when we start our mountain descent, I think we'll be more than happy. And we'll have a warm car! (That is, when we're finally ready to make a Tesla purchase.)

As an aside, I'll add that descending a mountain in an EV with adequate regen is a very pleasant experience. (Given a low SoC and/or a high battery temperature, our LEAF's regen can be very good.) It is so nice not to have to listen to the racket of engine braking all the way down, and controlling speed with regen is very smooth. Of course, ascending a mountain in an EV is also quite nice...

 

[bxr140]

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Thank you so much for the detailed response. This puts my mind at ease regarding the regen. As long as the regen is in the 15-30 kW range when we start our mountain descent, I think we'll be more than happy.

So...the problem is that constant regen may work against you.

I live at elevation (for the bay area, anyway...about 1500') and other than a hundred foot or so uphill to get out of my neighborhood, the first four miles of my commute has me decend 1200 feet. While I'm rarely pegging regen, I'm also rarely in the orange. Even on summer mornings I'll get regen limiting toward the end of the decent. Winter mornings are worse, but not by too much--I'm not sure if the fact that the cabin heater is on has anything to do with it? I park in my garage and sometimes ill also get limiting right off the bat in the winter, but that usually goes away by the time I get out of my neighorhood. The most limiting I think I've seen is to about 15kw, but I can't recall the conditions. Typically limiting gets down to 30kw or so. Obviously, its never horribly cold here.

At first I thought the phenomenon was some sort of overcharge protection, similar to the regen limiting you get near 100% soc. My energy consumption is always negative at the bottom of the decent (I finally flip back to positive consumption around mile 7 of my commute) and I've postulated that its simply the car not wanting to go 'more negative'. Unfortunately I have yet to find a convicing pattern linked to weather, soc, whether the car was plugged in the previous night, the charge limit setting, or any particular value of negative consumption to explain the "I dont want to regen anymore" theorem. I do know I wont get limiting if the car was recently driven or if its hot out, so that suggests it may have something to do with the fact that everything is cold. That's just a guess though, and not very convincing since its a relative cold, not a true winter cold. Ive also done other longer/steeper decents without tripping regen limiting, so that's at least a little more data to support the warming up theory.

I have no idea whether or not you'll see the same thing...hopefully someone smarter than me can essplain more.

 

[jerry33]

Thank you so much for the detailed response. This puts my mind at ease regarding the regen. As long as the regen is in the 15-30 kW range when we start our mountain descent, I think we'll be more than happy. And we'll have a warm car! (That is, when we're finally ready to make a Tesla purchase.)

15 will be a bit skinny. You really want close to 30. Understand I don't have a mountain descent, so my numbers are for more or less flat land.

 

[svp6]

So what do you guys do before leaving in very cold weather but are not connected to a charger. I have a commute where I need to leave the car outside, looks like ~0F. Any merit pre-heating the car from the car battery (other than feeling warm when I start driving)?

 

[apacheguy]

If you need the range, I wouldn't preheat without being plugged in. Better to use the heat from the motor as you drive.

 

[jerry33]

So what do you guys do before leaving in very cold weather but are not connected to a charger. I have a commute where I need to leave the car outside, looks like ~0F. Any merit pre-heating the car from the car battery (other than feeling warm when I start driving)?

Switch to range mode before driving*. Don't preheat unless plugged in.

* Some owners report that if you have a very long commute--more than 50 miles one way--there isn't any noticeable difference between range mode and not range mode. My commute is 25 miles one way and there is a noticeable difference.

 

[Andyw2100]

So what do you guys do before leaving in very cold weather but are not connected to a charger. I have a commute where I need to leave the car outside, looks like ~0F. Any merit pre-heating the car from the car battery (other than feeling warm when I start driving)?

Switch to range mode before driving*. Don't preheat unless plugged in.

* Some owners report that if you have a very long commute--more than 50 miles one way--there isn't any noticeable difference between range mode and not range mode. My commute is 25 miles one way and there is a noticeable difference.

jerry33--Are you giving the advice not to preheat unless plugged in because of range concerns? I ask because my wife just started taking the new P85D to work, which is about a 50 mile drive each way. It's been very cold, and for her trip in to work in the morning I'm trying to have the overnight charge end shortly before she's leaving, and I'm also having her pre-heat etc. But I've also suggested she pre-heat from battery power before she leaves work so that she has some regnerative braking when she first starts driving, and because I thought that was slightly better for the overall health/longevity of the battery. Range is not an issue, even in the cold, as she'll be setting out with about 225 miles of range to drive about 100 miles.

Have I been giving her bad advice, or is it fine for her to pre-heat from battery power before her trip home?

Thanks!

 

[jerry33]

jerry33--Are you giving the advice not to preheat unless plugged in because of range concerns?

Yes. Basically preheating from the battery lowers range more than letting the battery warm up from driving. As far as I know, there is no difference in battery life with either strategy because the car won't let you draw/regen so much power that the battery degrades.

Most times the lows here are from 0 C to -10 C. If it's colder where you live, preheating from battery increases driver comfort.

 

[Andyw2100]

Yes. Basically preheating from the battery lowers range more than letting the battery warm up from driving. As far as I know, there is no difference in battery life with either strategy because the car won't let you draw/regen so much power that the battery degrades.

Most times the lows here are from 0 C to -10 C. If it's colder where you live, preheating from battery increases driver comfort.

OK, good.

So the advice I gave her is fine, then.

If she's not at all concerned with range, and wants to have some regen available as soon as she starts driving, she should, in fact, do as I suggested and pre-heat the car, with range mode off, on battery power, and this will not cause any harm, battery degradation, etc. The only downside is loss of range.

Thanks.

 

[invisik]

So you're seeing running HVAC heat with Range Mode ON warms the battery to 15kw regen limiter? (versus 30kw limited with Range Mode OFF)

 

[jerry33]

So you're seeing running HVAC heat with Range Mode ON warms the battery to 15kw regen limiter? (versus 30kw limited with Range Mode OFF)

That's what I see. In Minneapolis, if you are parking outside, you aren't likely to see those numbers when it's very cold (-10C and below). The cold weather here is much closer to freezing. 0C to -5C is a pretty typical low for the day during a cold spell.