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Pre deparure battery pre heat. What temperature? Best way to preheat?
- Thread starter exlatccatsa
- Start date
MrBadger
Badger out
If you charge during a low carbon and/or cheap rate period, the energy is consumed from that period. If you pre-heat, the energy consumed is from the time just before the journey.
If you watch the climate screen in the app, or have something like TeslaFi, you can see how quick the car charges and how hot it gets, however its not the full story due to the location of the interior temperature sensor. But even so, its a small space with a lot of energy being put into heat it so it is very quick space heating. 5 minutes in any temperature will get the cabin nice and toasty. But it won't unfreeze the windows if frozen.
As for increasing efficiency for driving, imho, for a journey where range is not important, warming the battery is not important. I would much rather use energy stored when it was low carbon/cheap rate (5p plus charge losses) than use potentially high carbon at 14p/unit. The two identical journeys below done in similar conditions, the difference was negligible. Top journey, no pre heat, bottom journey cost us 7% battery pre heat and probably 2kWh in electricity, around 30p - we only charge at 10A - so if we charged at say 7kW, battery use would have been less, but electricity potentially twice the amount. Ordinarily, we would have pre heated at that temperature for 5-10 minutes, but went longer early morning because of risk of potentially frozen doors.
Putting that into context, below is the exact same drive as the bottom one but a week later and a bit warmer. No pre heat at all.
So for these journeys, the advantages of pre heating the battery was negligible and in the case of the pre heat, it cost nearly 30p and lost 7% battery. All for a real world benefit of less than a mile additional loss in range over the 14 mile journey (~7% range loss in this case).
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I used pre-heating a lot last winter, but my commute was well over 100 miles round trip with a long time for the battery to go cold again during the day. It made quite a difference to the amount of charge I returned home with on the commute leaving plenty of flexibility for the evenings. I was also really glad of the increased range on even longer journeys.
I understand wanting to work out the trade off between cost of preheating and efficiency return. I’d have to watch Nyland’s videos again to check the facts, but IIRC the preheating draws about 11kW for about 10-15 mins to heat both cabin and battery. After that it drops to about 6-7kW thereafter to continue warming the battery and the time it takes depends on how cold the battery was to start with and the outside temperature. In his tests it was 30-50 minutes I think, but it is a lot colder in Norway than the UK during the winter. For a crude estimate, let’s say it was 7kW for an hour or 7kWh. At @Jibjab’s 12.6p/kWh that’s under £1. If it were a short journey, I’d just pre-heat the cabin for 10 minutes. If range were a consideration, I’d pay the £1.
I understand wanting to work out the trade off between cost of preheating and efficiency return. I’d have to watch Nyland’s videos again to check the facts, but IIRC the preheating draws about 11kW for about 10-15 mins to heat both cabin and battery. After that it drops to about 6-7kW thereafter to continue warming the battery and the time it takes depends on how cold the battery was to start with and the outside temperature. In his tests it was 30-50 minutes I think, but it is a lot colder in Norway than the UK during the winter. For a crude estimate, let’s say it was 7kW for an hour or 7kWh. At @Jibjab’s 12.6p/kWh that’s under £1. If it were a short journey, I’d just pre-heat the cabin for 10 minutes. If range were a consideration, I’d pay the £1.
Thanks Vanilla and Jeeves. Max of 20mins ore heat unless it’s a road trip scenario 
My current energy provider have been horrendous and I’m still trying to sort the SMETS 2 gas meter out after 6 months. Once that’s done I might get more organised and look at Octopus Go/Agile etc. I have a hot tub that arrived at the same time as the car, so need to look at option as the next bill is going to be fun!
My current energy provider have been horrendous and I’m still trying to sort the SMETS 2 gas meter out after 6 months. Once that’s done I might get more organised and look at Octopus Go/Agile etc. I have a hot tub that arrived at the same time as the car, so need to look at option as the next bill is going to be fun!
> just depends when I remember
If it helps: You can use TeslaFi to schedule turning the HVAC on/off at set times. I appreciate you might not know precisely when your other half will leave - but it works pretty well here for a school run that can be +/- 15m. You can tweak the start time based on cold/warmer snaps too. 10-20m is the range I’ve used so far.
I noticed TeslaFi can also set the Max Defrost On (HVAC to HI?) if you expect the need to e.g. unfreeze the door handles.
HTHs
If it helps: You can use TeslaFi to schedule turning the HVAC on/off at set times. I appreciate you might not know precisely when your other half will leave - but it works pretty well here for a school run that can be +/- 15m. You can tweak the start time based on cold/warmer snaps too. 10-20m is the range I’ve used so far.
I noticed TeslaFi can also set the Max Defrost On (HVAC to HI?) if you expect the need to e.g. unfreeze the door handles.
HTHs
A couple of points about preheat that don't seem to be that common based on this and other similar threads:
1) I can easily achieve 0C => 28C cabin temperature in 5 minutes or less and do this multiple times a day. Why would I need to preheat for a longer period? I usually charge for around 30min before the first departure of the day in order to warm the battery a little.
2) When my 2020 M3 SR+ is plugged in and I do what is described above the battery % goes down 1-2 %. Isn't the car supposed to take the electricity from the outlet in this situation? Also, there is phantom drain during the night even when the car is plugged in, but that's normal, right?
3) If temperature is around 0C, do the batteries need to be warmed before driving for any other reason than to have the maximal range available?
1) I can easily achieve 0C => 28C cabin temperature in 5 minutes or less and do this multiple times a day. Why would I need to preheat for a longer period? I usually charge for around 30min before the first departure of the day in order to warm the battery a little.
2) When my 2020 M3 SR+ is plugged in and I do what is described above the battery % goes down 1-2 %. Isn't the car supposed to take the electricity from the outlet in this situation? Also, there is phantom drain during the night even when the car is plugged in, but that's normal, right?
3) If temperature is around 0C, do the batteries need to be warmed before driving for any other reason than to have the maximal range available?
As I understand it, the car runs inefficiently when the battery is cold i.e. it uses more energy to go the same distance. Charging the battery does cause it to get warmer, but the cabin preheat makes the front rotors run in some sort of way to warm up the battery coolant and so the pack temperature. I think this is a more significant warming effect than you get from charging alone and something unique to Tesla cars. I think it is the same thing as preconditioning for supercharging.
It might help to watch Bjørn Nyland’s videos, but as I understand it, the cabin heater and the rotors come on and draw about 11kW. Don’t know what supply you have in Finland, but most of us have only 7kW so it would represent a net loss for a bit.
Yes phantom drain is normal, but I don’t think that is really contributing to the 1-2% loss you’re describing.
Related, but regenerative braking is significantly reduced when the battery is cold.
