Baffled by preconditioning

[EV1980]

Looking for some advice from more experienced owners about 'preconditioning'. Apologies in advance if this comes across as incoherent ramblings!

As I understand it, preconditioning warms the inside of the car and preheats the battery, meaning the car is already primed before you drive off and as a consequence this leads to increased efficiency. Am I correct?

I've read that the car should be plugged in when preconditioning - I assume this is so that the energy required to precondition is provided by the charging unit rather than the car's battery? Again, am I correct?

I plugged the car in last night and drove to work today after preconditioning and was suitably impressed by the efficiency. However, have I simply just used (and paid for) additional electricity to precondition. Would I have been any better off preconditioning without being plugged in, or perhaps not preconditioning at all?

How often do you precondition? is it all the time? Only under a certain temperature? etc... Does anyone precondition all the time in winter in the UK?

In case it makes any difference my daily commute is 28 miles each way, about 19 of which are on a motorway. I'm planning to ensure I start every Monday morning with the battery topped up to near 100% and then perhaps stick it on charge again mid week to get me through until going home on Friday evenings. I'd rather not plug it in just to precondition if i'm not actually looking to charge it but perhaps the answers to this post will educate me a little better. This week looks set to be a cold one for us Brits so it should be a good experiment for the new owners amongst us.

Thanks.

 

[MrBadger]

I plugged the car in last night and drove to work today after preconditioning and was suitably impressed by the efficiency. However, have I simply just used (and paid for) additional electricity to precondition. Would I have been any better off preconditioning without being plugged in, or perhaps not preconditioning at all?

How often do you precondition? is it all the time? Only under a certain temperature? etc... Does anyone precondition all the time in winter in the UK?

Yep. You've got it. Unless you need the extra range where paying peak home rate to get to your destination might be cheaper/more convenient than topping up along the way, its going to be cheaper (and likely better for the environment) to not/only very short precondition at off peak times.

Unfortunately, heating the car is sometimes the only way of getting inside, so if I know its going to freeze overnight, I normally unplug and pre heat the car solely from battery. I just wish there was an option to select where the car gets its preheat energy from, batter and/or car. Its also going to help home battery users who may want to preserve their home battery usage for things where there may not be an alternative cheap source of energy.

 

[Jason71]

I don't use the automated feature but I do it manually daily in winter but only to heat the cabin. I switch the heater it on 5-10 minutes before leaving the house. This is more than adequate to warm the cabin unless its actually subzero and icy.
Currently my day rate is only 13.5p so I leave it plugged in but that is about to change at which point I will be tempted to unplug the car before starting the heating.
The only time I do a full 20+ minute preheat to warm the battery is if I am doing a long journey and wish to maximise the range

 

[spooksman]

I don't use the automated feature but I do it manually daily in winter but only to heat the cabin. I switch the heater it on 5-10 minutes before leaving the house. This is more than adequate to warm the cabin unless its actually subzero and icy.

Same here since I got the car in 2020. When it is cold I normally nip out to see if the windows are icy and go from there. If the car is plugged in I unplug it, especially as peak rates on IO are high!

Having said that, I have not scraped the ice of a car for three years - bliss

 

[EV1980]

Thanks All. I can see the sense in looking out the window when I get up and choosing to warm the car manually from the app before leaving the house rather than setting a scheduled preconditioning time.

I think i'll leave it unplugged tomorrow and warm it up 5 or 10 mins before leaving the house while i'm having my breakfast and see how different my Wh/Mi reading is compared to today's trip. (I accept tomorrow's temperature and weather conditions may be more detrimental)

Possible silly question - Does warming the inside of the car also automatically warm the battery or not?

 

[Simavon]

At 7.5p/kWh overnight vs 40.9 by day, I will not precondition from mains (but yes to solar) unless I know I will be going on a long trip where I'll need to pay a much higher rate for rapid charging.

 

[qwickshot]

Thanks All. I can see the sense in looking out the window when I get up and choosing to warm the car manually from the app before leaving the house rather than setting a scheduled preconditioning time.

I think i'll leave it unplugged tomorrow and warm it up 5 or 10 mins before leaving the house while i'm having my breakfast and see how different my Wh/Mi reading is compared to today's trip. (I accept tomorrow's temperature and weather conditions may be more detrimental)

Possible silly question - Does warming the inside of the car also automatically warm the battery or not?

It only takes 2-3 mins to heat the cabin from cold but that energy is not taken into account on the ‘trip computer’ so the efficiency will probably be the same.

It does start warming the battery but in reality you don’t need it to unless it’s stone cold and you are planning some drag races.

I’d also not charge to 100% daily, you don’t need it and if you are at 100% regen is reduced and you are leaving efficiency on the table (more so in the spring-autumn period where regen is t also limited by battery temperature).

Charge it to 80% daily and then once a week to 100% if you have an LFP battery or if you need the extra range.

 

[EV1980]

It only takes 2-3 mins to heat the cabin from cold but that energy is not taken into account on the ‘trip computer’ so the efficiency will probably be the same.

It does start warming the battery but in reality you don’t need it to unless it’s stone cold and you are planning some drag races.

I’d also not charge to 100% daily, you don’t need it and if you are at 100% regen is reduced and you are leaving efficiency on the table (more so in the spring-autumn period where regen is t also limited by battery temperature).

Charge it to 80% daily and then once a week to 100% if you have an LFP battery or if you need the extra range.

Thanks qwickshot, i agree with your advice on charging and the App also says to charge to 100% just once a week. The rest of the time i'll just keep the battery within the 25%-80% range.

 

[Ashdeman]

At 7.5p/kWh overnight vs 40.9 by day, I will not precondition from mains (but yes to solar) unless I know I will be going on a long trip where I'll need to pay a much higher rate for rapid charging.

This. I like getting into a nice toasty car in the morning (especially on my early shift pattern) but I let it use the battery which has the cheap electrons from the overnight rate. If I was going on a trip where I needed to maximise range then I'd precondition from mains.

 

[Astrape]

This. I like getting into a nice toasty car in the morning (especially on my early shift pattern) but I let it use the battery which has the cheap electrons from the overnight rate. If I was going on a trip where I needed to maximise range then I'd precondition from mains.

Hi waiting room / spec buddy

Warming the battery on the RWD / LFP car also reduces the time before reduced regen stops showing. I know this because on leaving my house the first couple of miles may be downhill to the river dodging around parked cars all through the village. With preconditioning doing this on lift off regen braking works, without I will be using the disc brakes sometimes to pull in behind a car as someone comes up. I just take it as an opportunity to clean up the discs, but it does feel odd to feel the brakes bite each time. One pedal driving becomes so comfortable.

 

[Astrape]

Possible silly question - Does warming the inside of the car also automatically warm the battery or not?

In RWD cars only slowly. There is a limited amount of heat generation available from one motor about 3kW. I dont know what the exact times are, but it takes only a few minutes to warm up the cabin, but much longer to see the green regen warning due to cold battery go away.

I was with a colleague with an MYLR last week and he commented when he had a try of my car that after we were at a customer for a couple of hours, with 6 degree outside, my M3 RWD showed the green warning sign, whereas at that temperature the LR would not. This shows how LFP batteries are fussier about the cold.

 

[EV1980]

Thanks Astrape, so are you saying that RWD cars benefit more from preconditioning than LR cars, as a result of it aiding regenerative braking? If I've read that right, maybe the energy used to precondition is offset by more efficient braking/driving?

Any idea at what temperature preconditioning becomes null and void?

 

[Ferret]

I precondition with the car plugged in for convenience. I guess I could automate turning the AC on 15 mins before departure, but I definitely wouldn't bother doing it manually to save some pence at certain times of the year.

 

[SageBrush]

OP, I suggest you clarify what you are seeking. "Efficiency" means different things to different people

Comfort ?
Convenience ?
Money savings ?
Range ?
Performance ?
Energy reduction ?
Pollution reduction ?

You correctly guessed that these parameters are trade-offs. And as for Wh/mile, keep in mind that pre-conditioning from shore power is not counted by the car when calculating Wh/mile.

My personal version of juggling these things was to turn on seat heating a couple of minutes before I used the car in the winter. If the windows have snow/ice I would turn on defrost, manually scrape, and turn it off once the windows were clear.

 

[NickFie]

"Efficiency" means different things to different people

Efficiency-there is power loss when charging the battery from mains. There is additional power loss pulling the energy from the battery. Thus, pre-conditioning from mains spins the utility meter less for a given amount of heat.

Also, a pre-conditioned battery recaptures more regeneration energy, reducing net utility power consumption.

Economy-if utility power is relatively costly during pre-conditioning, then power “arbitrage” - buy low, sell high - makes sense. Disconnect/disable charger before pre-conditioning. Then you consume low-cost power from the battery.

 

[SageBrush]

Efficiency-there is power loss when charging the battery from mains. There is additional power loss pulling the energy from the battery. Thus, pre-conditioning from mains spins the utility meter less for a given amount of heat.

I don't think so. That is time-shifted metering since the energy taken from the battery is replenished later from the mains.
I agree that regen performance is improved with a warmer battery. As OP figured out though, a driver can often decide to coast more instead of brake. That is how I drive, and it is around 50% more efficient than regen. Moreover, regen is usually not in play on the motorway.

Disclaimer: I use "efficiency" in an engineering sense, meaning useful_work/energy_consumed

 

[NickFie]

don't think so. That is time-shifted metering since the energy taken from the battery is replenished later from the mains.
<snip>

Disclaimer: I use "efficiency" in an engineering sense, meaning useful_work/energy_consumed

We agree about the definition of efficiency.

Less than 100% of mains power reaches the battery during charging. There is small energy loss traversing the vehicle’s onboard AC-DC charger and in the battery’s charge chemistry process. Since this occurs well before or after departure, the lost energy performs no useful work. Teslafi.com shows charge efficiency in the mid-90s percent for our S & 3 during home charging.

In this scenario we can overlook the energy lost to chemistry and internal resistance when the battery discharges during conditioning since that energy directly heats the battery.

Thus, conditioning while on mains power consumes fewer KWh of mains power than conditioning from the battery’s stored power.

Conditioning from mains power is less expensive if one is on a flat-rate plan. If off-peak discount is available, then it is less expensive to condition with inexpensive stored power.

 

[avs007]

It does start warming the battery but in reality you don’t need it to unless it’s stone cold and you are planning some drag races.

Actually, warming the battery is important, if you need the regen, like if you live on a hill like I do... Where even if its 50 degrees outside, I'll have reduced regen, unless I pre-warm the battery... I don't really care about the extra "efficiency" with a warm battery... I care about not having to stand on the brakes when descending a 12% incline.

 

[starharbour]

Thanks to to the OP and the responders for the info on this topic. Since getting my M3 a month ago, I've been slowly learning all the ins and outs of the battery. I've long too been debating the cost/benefit of preconditioning the battery versus not.

What i've concluded is the follows:

- Preconditioning is important to me, because it drives me mad to have reduced regen-braking, even for relatively short journeys
- However, it is not worth it if my car is preconditioning from the mains at peak hours. My peak rate is 45p/kwh and offpeak 10p/kwh. I'm much happier to have my car charge at off peak times and then eat a couple of percent from the battery to precondition rather than paying 2-3kw at .45p every time I want to leave the house in the morning.
- I thought there was a fault with my M3 with the "battery status bar" at the top. It NEVER reaches far left - e.g. there's always about an inch of . . . . . . before the line turns solid. From reading this forum, my understanding is that this is normal and no cars ever get 100% full regen braking... am i correct here?

Thanks!

 

[Ashdeman]

Thanks to to the OP and the responders for the info on this topic. Since getting my M3 a month ago, I've been slowly learning all the ins and outs of the battery. I've long too been debating the cost/benefit of preconditioning the battery versus not.

What i've concluded is the follows:

- Preconditioning is important to me, because it drives me mad to have reduced regen-braking, even for relatively short journeys
- However, it is not worth it if my car is preconditioning from the mains at peak hours. My peak rate is 45p/kwh and offpeak 10p/kwh. I'm much happier to have my car charge at off peak times and then eat a couple of percent from the battery to precondition rather than paying 2-3kw at .45p every time I want to leave the house in the morning.
- I thought there was a fault with my M3 with the "battery status bar" at the top. It NEVER reaches far left - e.g. there's always about an inch of . . . . . . before the line turns solid. From reading this forum, my understanding is that this is normal and no cars ever get 100% full regen braking... am i correct here?

Thanks!

100% regen has been rare in my RWD M3 over the winter months unless I've been on a long journey. Once the outside temp gets to around 15°C though I've seen 100% regen on my 12 mile commute, that's with a couple of mins preconditioning to warm the cabin.

As I understand it the motor is what generates the heat for the battery so LR and Performance models will heat the battery quicker since they have the additional motor.