Battery preheat released

[Big Earl]

This preheating thing is strange to me. My car is garage parked, but by garage is only partially insulated so today, the car's temp was at +1. I started to preheat at 7:40am. I preheated until 8:25am. Car was plugged in the entire time.

Got in the car and I only had about 1/2 regen permitted. I just figured after 45 minutes of preheating, it would have warmed up sufficiently to allow for full regen. I also figured that it wasn't that cold inside the garage.

I then drove to work which is only a short 10 minute drive and I never got to full regen. Not really a big deal, but I figure I might be doing something wrong.

A couple of observations:

1.) Preheating will only warm the battery enough for about 1/2 regen, which can take up to 45 minutes in very cold weather
2.) You are consuming a huge amount of energy to heat up your car for a 10 mile drive to work

Full regen is nice to have, but it isn’t necessary on a short commute. You will save a lot of energy if you preheat just long enough for the cabin to be comfortable. I see no reason to preheat the battery for such a short trip when it’s just going to cold soak again at your destination.

 

[MorrisonHiker]

A couple of observations:

1.) Preheating will only warm the battery enough for about 1/2 regen, which can take up to 45 minutes in very cold weather
2.) You are consuming a huge amount of energy to heat up your car for a 10 mile drive to work

Full regen is nice to have, but it isn’t necessary on a short commute. You will save a lot of energy if you preheat just long enough for the cabin to be comfortable. I see no reason to preheat the battery for such a short trip when it’s just going to cold soak again at your destination.

I agree. My commute is also only about 10 miles and I see no need to warm the battery and cabin for an hour if I have a 10 minute drive. Unless it is really cold, I don't even bother heating the car up since the seat heaters do a good job of keeping me warm on my brief commute.

 

[IT Geek]

Indeed. The Chevy Volt has had this capability since 2012.

Someone needs to Tweet at Elon then the next time he's drinking wine or taking suggestions. ( I don't use Twitter, but maybe I should )

 

[wayner]

It would be nice if the App allowed you to schedule the recharge so that the car was finished charging at a given time each day. Some might want to start their charging at 4:00 in the morning all the time, but I'd rather see it finish at 7:30. Yeah, I know there's an App for that..but I think this should be a Tesla feature.

I agree. I wrote some code in Python to do this a year or two ago although I am not running it currently. The issue is that you have to know your charge rate to be able to accurately forecast how long it will take. Plus you need to add in extra time in very cold temps.

Here is my charge curve from TeslaFi for this morning. You can see that it takes about 17 minutes until my car starts fully charging (orange line flatlines) - I guess that is due to the cold temps. (I currently have my HPWC set at 70A). It doesn't show on this graph but the "outside" temp (the temp in my garage) was -1.5C.

It would be interesting to know how to calculate this delay - it is 17min at -1.5C - how long at colder temperatures? Can you come up with a linear approximation like (time to warm)= -1*(temp-15) - so you need 1 minute of warmup time for each degree below 15C.

 

[wayner]

( I don't use Twitter, but maybe I should )

You just lost Geek cred points there IT Geek

 

[mknox]

IHere is my charge curve from TeslaFi for this morning. You can see that it takes about 17 minutes until my car starts fully charging (orange line flatlines) - I guess that is due to the cold temps. (I currently have my HPWC set at 70A). It doesn't show on this graph but the "outside" temp (the temp in my garage) was -1.5C

That is really interesting. My garage is around the same temperature. I don't use TeslaFi, but I do have a sub-meter on the circuit to my car. It just jumps to the full 40 amps I have my HPWC set at and stays flat until charging completes. Presumably, some of that energy is going to heat the battery before it actually starts charging the battery in that 17 minutes. Too bad you can't see where all of the energy coming in the charge port is going to determine how much is being dedicated to heating (but I guess you could calculate it).

EDIT: But then, why is the "charger current" tapered like that? I would think that any HVAC energy has to go through the on-board chargers as well???

 

[ShawnA]

Sorry for the question in the wrong forum...
I have seen repeatedly that the heater for the Model S is 6 Kw.
What size is the battery heater for the Roadster 2.X ???

Thank You, Shawn

 

[Doug_G]

Hmm... I honestly don't remember clearly. Something in the 3-4 range I believe.

 

[ThosEM]

Late to the party; just tried this out for the first time: Interesting!
Car was at 5C indicated interior temperature, charged to 90%/368 km in my garage, connected.
Turned on climate, set to 20C, and it started ramping up quickly.
When it hit about 8 or 10C, the red battery heating indicator came on.
Interior temp overshot a bit to 22C, then settled back to 21C.
The battery heating indicator remained on for about 5 more minutes, then went out.
I turned off the climate and the interior started cooling back down.
There was no appreciable change in the charge state (indicating 368 km rated range).

It would be better to have separate actuators for the cabin and the battery heaters and of course we'd like to see a battery temperature indicator (beyond the regeneration limit) to match the cabin temperature indicator. I suppose the Tesla attitude is to prevent one from being troubled by things that are supposed to be automatically taken care of. But if they carried that to the logical conclusion, we would simply indicate to the app our desired departure time, and the car would be managed to a state of readiness by that time. Or we would take off in it before it was fully ready.

I guess there is no question that an EV is best warmed up before departure in cold weather?

 

[wayner]

I guess there is no question that an EV is best warmed up before departure in cold weather?

No question - but the best way to do this is by charging. @Doug_G wrote an excellent blog about this a couple of years ago.

I had no regen limits on my car this morning when I left as it had been charging for 3.5+ hours at 70A and just stopped charging 10 minutes before I left for work. (See above graph - I left at 7:45)

 

[Doug_G]

No question - but the best way to do this is by charging. @Doug_G wrote an excellent blog about this a couple of years ago.

FYI, Cold Weather Driving

 

[David99]

This preheating thing is strange to me. My car is garage parked, but by garage is only partially insulated so today, the car's temp was at +1. I started to preheat at 7:40am. I preheated until 8:25am. Car was plugged in the entire time.

Got in the car and I only had about 1/2 regen permitted. I just figured after 45 minutes of preheating, it would have warmed up sufficiently to allow for full regen. I also figured that it wasn't that cold inside the garage.

I then drove to work which is only a short 10 minute drive and I never got to full regen. Not really a big deal, but I figure I might be doing something wrong.

Nothing wrong. The battery allows zero charging and zero regen when it is 0 deg Celsius. It is important to distinguish between outside temperature, inside temperature and battery temperature. What matters for pre-heating and regen is the battery temperature. The battery temperature is not visible to the user.

The new preheating feature warms up the battery to aprox 12 Celsius using the battery heater. Before that feature was implemented, the battery heater would warm up the battery to only 8 Celsius.
Regenerative braking is disabled at 0 Celsius or lower and is fully available at 20 Celsius (again battery temperature, not ambient nor inside the car). So this new feature just gives you a little more regen by warming up the battery a little warmer than before. That's really all it is. The only other thing is that the app will now show when the battery heater is on.

 

[Big Earl]

I guess there is no question that an EV is best warmed up before departure in cold weather?

I would say it depends on what you’ll be doing with the car. I’ve come to the conclusion that the only reason to heat the battery is to recover “trapped” range (due to cold temperature), provide regenerative braking and to charge.

If your destination is a short distance away, perhaps 20 or fewer miles, the energy required to heat the battery will provide little benefit. If you’re embarking on a longer trip where regenerative braking is desired or you plan on supercharging, it makes sense to preheat the battery, as that energy will go to good use.

 

[David99]

It would be interesting to know how to calculate this delay - it is 17min at -1.5C - how long at colder temperatures? Can you come up with a linear approximation like (time to warm)= -1*(temp-15) - so you need 1 minute of warmup time for each degree below 15C.

What matters is only the battery temperature, not the ambient or car's inside temp. If your battery is warm and you park it over night in cold weather, the battery might still warm enough to not even need the battery heater on in the morning. A car that has been driven little in days and parked in the same weather conditions will have a much colder battery thus needing significant battery heater in the morning.

You cannot compare based on ambient temperatures. The battery temperature is all that matters and it's unavailable to the user, thus it can't be used to calculate the extra energy needed to warm up the battery in the morning. I did some tests looking at the CAN bus (where battery temp and lots of other things are available) and it took about 7 kWh to warm my battery up from -8 C to 12 C (that's the point where the battery heater stops).

 

[Big Earl]

What matters is only the battery temperature, not the ambient or car's inside temp. If your battery is warm and you park it over night in cold weather, the battery might still warm enough to not even need the battery heater on in the morning. A car that has been driven little in days and parked in the same weather conditions will have a much colder battery thus needing significant battery heater in the morning.

You cannot compare based on ambient temperatures. The battery temperature is all that matters and it's unavailable to the user, thus it can't be used to calculate the extra energy needed to warm up the battery in the morning. I did some tests looking at the CAN bus (where battery temp and lots of other things are available) and it took about 7 kWh to warm my battery up from -8 C to 12 C (that's the point where the battery heater stops).

Very interesting. Does that 7 kWh include cabin heat or did you set the cabin temp to LO so that it wouldn’t consume as much energy?

 

[wayner]

What matters is only the battery temperature, not the ambient or car's inside temp. If your battery is warm and you park it over night in cold weather, the battery might still warm enough to not even need the battery heater on in the morning. A car that has been driven little in days and parked in the same weather conditions will have a much colder battery thus needing significant battery heater in the morning.

You cannot compare based on ambient temperatures. The battery temperature is all that matters and it's unavailable to the user, thus it can't be used to calculate the extra energy needed to warm up the battery in the morning. I did some tests looking at the CAN bus (where battery temp and lots of other things are available) and it took about 7 kWh to warm my battery up from -8 C to 12 C (that's the point where the battery heater stops).

I agree totally with what you are saying but I can't get the battery temp from the API. On weekdays my car generally sits idle in my garage from 6:10 pm until 7:10am. I only drive a short while to the train station and back. So I am making an assumption that the ambient temperature in the garage is good enough to use as an estimate for a formula like that to estimate warmup time. In very cold weather I don't think the battery will stay warm sitting for 13 hours - certainly that is not my experience in three years driving a Tesla in Canada.

My previous algorithm did not have any adjustments for temperature - I just added a 5-10 minute buffer. Most days that was fine. I like my charging to end at 7:00 as that is when a higher electricity rate kicks in here in Toronto. (today was an exception as I left home late and let the car charge later).

 

[claudelaval]

just was an update to my Tesla app: battery preheat is now available provided your car has v.50 or better.

I’m still on v46, so I’ve gotta wait to test it.

v.50 or better what is that?

 

[claudelaval]

It ask to start preheat in the car 1 hour before driving.

I thought it stops after 30 minutes

 

[David99]

Very interesting. Does that 7 kWh include cabin heat or did you set the cabin temp to LO so that it wouldn’t consume as much energy?

It does include cabin heating. Total time I measured was 45 min.

Energy consumption for Preheating

 

[Doug_G]

I would say it depends on what you’ll be doing with the car. I’ve come to the conclusion that the only reason to heat the battery is to recover “trapped” range (due to cold temperature), provide regenerative braking and to charge.

That sounds like a silly idea. It takes more power to warm the pack than you recover. In fact most of the time there is no "trapped" range showing on the display to be recovered, and it still takes a bunch of kWh to heat the pack.

I thought it stops after 30 minutes

It used to. I think since they implemented "Camper Mode" it may continue running the heat until you turn it off, or drive off and then park again, or the car gets down to 20%.