Battery preconditioning in cold weather

[AndysComputer]

Before we got our EV's I was watching YouTube videos and reading blog posts and now we have our Mini and I'm messing around with testing various aspects of it my mind dimly recalled this article on here about the i3:

https://insideevs.com/news/325863/bmw-i3-how-preconditioning-works/

Given the i3 and Mini share the same drivetrain and presumably electronics I was wondering if anyone can confirm my belief on how preconditioning works:

1. If you use the app to turn on the climate, let's say a few minutes before you want to leave, it simply heats the cabin. If plugged in at the time it uses wall power to do so, if not it uses battery power. If plugged in and there is not enough power from the wall, say the level 1 EVSE, it uses what it can from the wall and mixes in a bit of battery power to make up the difference.

2. There is no battery warming function on the i3 or Mini, ie it is not something you can turn on via the app or the in-car screens.

3. If you set a charge window and departure time in the app, the car will preheat the cabin by that time and delay charging the battery such that it finishes charging just before you leave and that charging will create heat in the battery and thus pre-condition it. This is the only mechanism by which the car can heat the battery, as a side effect of charging. It has no dedicated battery heating system or logic.

4. If the car has a full battery then that cannot be heated for your departure time, only the cabin.


I can see no sources to any of this beyond Tom's article so I am assuming it is the battery charging that is in essence preconditioning the battery. This is very different than the Tesla Supercharger preheating which uses battery energy to heat it as you are driving towards a Supercharger via GPS.

Have I understood this correctly?


I ask as I am going to do a range test at 5am tomorrow morning before work as it will be 1 degree above freezing and the battery is currently at 92%. I set the charge window to 8pm to 5am (which is our free electricity period on our plan) and a departure time of 5am. So I am thinking it will start charging probably at around 4am or just after, in order that full charge is reached by 5am along with a warm battery (I don't know how much charging is needed to effectively heat the battery but I assume 45mins worth on L2 is better than nothing) and the cabin is up to temperature. At least I'm hoping this is what happens...

 

[Carsten Haase]

This document is about the i3 but a lot should be similar between the two. I don't think it directly answers your questions but should be interesting! (I posted this somewhere else previously but can't find the thread)

The heat pump diagram on page 47 shows that there is no refrigerant flow to the batteries in heating mode (only flow during cooling) so there is no preheating function other than self heating through use.

 

[methorian]

I can't say for the Mini - but for the i3 it does pre-condition the battery (even at 100% SoC) IF you have a departure time set in the app at least 3 hours in advance.

IE - You'll need to set the departure time more than 3 hours before you're ready to depart. Doing this will pre-condition both the cabin temp and the battery.

 

[Puppethead]

The SE has no battery preconditioning, the only way to warm up the battery is to charge or drive.

The climatization (cabin warming/cooling) is separate from the charge window. Climatization basically runs off the 12 V battery (like most cars), with the high-voltage system used to keep the 12 V battery charged. Climatization will do very little to heat the high-voltage batteries, as I can attest to since I had that exact scenario this morning with subzero temperatures:

• SE (in garage) finished charging at about 11pm. Outdoor temperature dropped to at least -15 ºF overnight.
• Climatization departure time set for 7:30am; cabin was nice and warm for departure.
• Vehicle was at 100% SoC, but only 70% e-power due to coldness of battery.
• By the end of my 40-mile commute the battery was up to 100% e-power, outdoor temperature climbed to -8 ºF.

 

[Carsten Haase]

The SE has no battery preconditioning, the only way to warm up the battery is to charge or drive.

Climatization basically runs off the 12 V battery (like most cars), with the high-voltage system used to keep the 12 V battery charged.

I don't think that's true... A 12V resistive heater or a 12V heat pump/compressor would require very high currents to get the required power.

From the i3 manual at least, these components are HV:


(EKK is the AC compressor/heat pump)

 

[AndysComputer]

This document is about the i3 but a lot should be similar between the two. I don't think it directly answers your questions but should be interesting! (I posted this somewhere else previously but can't find the thread)

The heat pump diagram on page 47 shows that there is no refrigerant flow to the batteries in heating mode (only flow during cooling) so there is no preheating function other than self heating through use.

Huge thanks for that document, it explains it all very well and I'd be surprised if the Mini operate differently given that BMW wanted to recover their engineering budget from the i3 through re-use in the Mini.

Preheating/Precooling of the passenger compartment and optionally the high-voltage battery unit during the charging procedure at the departure time terminates

Dodgy English aside, that statement combined with the flow diagram and description of the same convince me that your statement is correct, the only form of battery pre-conditioning possible is a side effect of charging which of course heats it up.

 

[AndysComputer]

I can't say for the Mini - but for the i3 it does pre-condition the battery (even at 100% SoC) IF you have a departure time set in the app at least 3 hours in advance.

IE - You'll need to set the departure time more than 3 hours before you're ready to depart. Doing this will pre-condition both the cabin temp and the battery.

Do you have any source for the pre-conditioning at 100% SOC? That document provided above doesn't seem to show how that could be possible. It doesn't go into battery charging details so unless there is a way to pull power from the battery (where would it go?) and thus charge it to keep it at 100% s it were while heating it up...

 

[AndysComputer]

The SE has no battery preconditioning, the only way to warm up the battery is to charge or drive.

The climatization (cabin warming/cooling) is separate from the charge window. Climatization basically runs off the 12 V battery (like most cars), with the high-voltage system used to keep the 12 V battery charged. Climatization will do very little to heat the high-voltage batteries, as I can attest to since I had that exact scenario this morning with subzero temperatures:

• SE (in garage) finished charging at about 11pm. Outdoor temperature dropped to at least -15 ºF overnight.
• Climatization departure time set for 7:30am; cabin was nice and warm for departure.
• Vehicle was at 100% SoC, but only 70% e-power due to coldness of battery.
• By the end of my 40-mile commute the battery was up to 100% e-power, outdoor temperature climbed to -8 ºF.

It's great you are in extreme cold because I cannot test for that!
If I am following correctly your car had charged up to full by 11pm instead of waiting to charge with a view to finishing by the departure time. Hence your battery was not pre-conditioned and thus the power bar issue you saw.

Do you have a charge window configured together with a programmed departure time? I'm curious why it finished charging at 11pm instead of waiting until later to even begin charging? Mine normally starts at 8pm because my smart EVSE dictates that, but I don't use pre-conditioning. Now that I want to, I have added a charging window (which starts a minute after the smart EVSE allows it) AND a departure time of 4:59am so in theory I should not see the Mini start charging at 8:01pm like I normally do, it should wait until the early hours of the morning and *if* that happens then I'll have my nicely warm battery in addition to the cabin.
Your experience has me concerned that it won't happen that way though. So let's see what happens tonight...

 

[FrankinCarp]

Before we got our EV's I was watching YouTube videos and reading blog posts and now we have our Mini and I'm messing around with testing various aspects of it my mind dimly recalled this article on here about the i3:

https://insideevs.com/news/325863/bmw-i3-how-preconditioning-works/

3. If you set a charge window and departure time in the app, the car will preheat the cabin by that time and delay charging the battery such that it finishes charging just before you leave and that charging will create heat in the battery and thus pre-condition it.

...

Sorry but the charging is not delayed to just before your departure time. That seems to be a commonly held belief.

My charging slot is set for 7 pm to 7 am. Even if I set a departure time of 6:00 am, my MINI will start charging at 7 pm and will complete to 100% without a delay to match my departure time setting.
I get an alert on my iPhone (and Apple Watch) when the 100% charged level is reached. That is generally some time around 9:30 pm.
At 6:00 am , Mike Wazowski is nice and toasty warm with the climatization having started about 15-20 minutes beforehand.
Typical temperature these days in the unheated garage is between -8° to -19°C


Sent from my iPad using Inside EVs

 

[AndysComputer]

That's good to know.
Therefore I expect to see the Mini start charging at 8:01pm when the slot opens, it'll be done probably 8:45pm, and at 5am when I head to the car the cabin will be at 21degC but the battery will not be pre-conditioned however I may not see any power bar drop because here it will be 0degC and maybe that's not cold enough to be a problem...
Will report back!

 

[methorian]

Do you have any source for the pre-conditioning at 100% SOC? That document provided above doesn't seem to show how that could be possible. It doesn't go into battery charging details so unless there is a way to pull power from the battery (where would it go?) and thus charge it to keep it at 100% s it were while heating it up...

This section of the linked article in the OPs post explains it:


It’s always been mentioned that way on all the i3 forums/etc and based on how early I see my i3 start pulling power from my EVSE of a morning (while at 100% SoC) I’m led to believe it’s true.

 

[AndysComputer]

The 3 hour thing…

So you see the car start drawing power 3 hours before departure even with a 100% state of charge? I can’t understand what it would be doing though to heat up the battery? The diagram shows only cold coolant flow to the battery and the use of the heat exchanger to get it…
I’ll keep an eye on that power draw on my EVSE to see how much it pulls and when it starts pulling it!

 

[methorian]

The 3 hour thing…

So you see the car start drawing power 3 hours before departure even with a 100% state of charge? I can’t understand what it would be doing though to heat up the battery? The diagram shows only cold coolant flow to the battery and the use of the heat exchanger to get it…
I’ll keep an eye on that power draw on my EVSE to see how much it pulls and when it starts pulling it!

Here’s some info from my EVSE integration into Home Assistant. It’s not perfect cause of the integration not always updating but the left bit is me plugging in after getting home and the i3 immediately starting to charge to 100%. It reaches 100% SoC around 9PM (disregard the gaps, it was charging the whole time). No more power is delivered until 2:45AM for a short period and then more power at 5:07 which is constant until my departure time of 5:45AM. You can see it even pulls up to 6kW at one point.



Car was outside in 20-25F temps and departure time of 5:45AM with pre-conditioning on.

I don’t think all that power was going just to cabin conditioning.

 

[Puppethead]

I don't think that's true... A 12V resistive heater or a 12V heat pump/compressor would require very high currents to get the required power.

You are likely right, I made an assumption (clearly wrong) based on how ICE cars heat/cool. I now realize the two errors in my assumption: 1) when the A/C kicks in on an ICE car you can feel it drawing on the engine, and 2) gas engines make their own heat as a waste byproduct.

 

[Carsten Haase]

The 3 hour thing…

So you see the car start drawing power 3 hours before departure even with a 100% state of charge? I can’t understand what it would be doing though to heat up the battery? The diagram shows only cold coolant flow to the battery and the use of the heat exchanger to get it…
I’ll keep an eye on that power draw on my EVSE to see how much it pulls and when it starts pulling it!

Is it possible that it's doing the model 3 thing and just stalling the motor? As far as I know that's unique to Tesla but might be something similar?

 

[MichaelC]

Sorry but the charging is not delayed to just before your departure time. That seems to be a commonly held belief.

My charging slot is set for 7 pm to 7 am. Even if I set a departure time of 6:00 am, my MINI will start charging at 7 pm and will complete to 100% without a delay to match my departure time setting.

That's interesting. When I use the time slot charging, my SE definitely delays so it completes charging shortly before my set departure time. When I plug it in, the app notifies me that charging is paused and it will be finished by ~<departure time>.

However, I do not activate the climate control.

I wonder if activating the climate control feature causes the SE to start charging immediately? Possibly to make sure the climatization doesn't accidentally prevent the SE from achieving full charge by the departure time?

 

[Puppethead]

It's great you are in extreme cold because I cannot test for that!
If I am following correctly your car had charged up to full by 11pm instead of waiting to charge with a view to finishing by the departure time. Hence your battery was not pre-conditioned and thus the power bar issue you saw.

Do you have a charge window configured together with a programmed departure time? I'm curious why it finished charging at 11pm instead of waiting until later to even begin charging?

I'm going to be one of the more extreme cold weather testers, I believe .

I do have a charge window set, but in this particular instance I plugged in after the window started so the SE started charging immediately.

Sorry but the charging is not delayed to just before your departure time. That seems to be a commonly held belief.

It is delayed until departure (at least on my 2021 SE). There are a couple of caveats, however:

1. The SE will start charging immediately if connected after the start of the low-cost window.
2. If the departure time is 30 minutes or more after the end of the low-cost window, the SE will charge immediately in the window.

For #2, I ran a series of tests to determine the 30-minute threshold, since I want my car to start charging at the beginning of the low-cost window. Except in these cold winter temperatures I moved my window close to my departure time and it delays until I leave.

 

[AndysComputer]

So I will add last nights experience to this…

12 hours before I wanted to depart I configured the charge window and departure time. A key thing may be that the car was already plugged in at this time?
Why?
It started to charge at 8:01pm, ie as soon as the charge window opened.
No delay to finish by the departure time.

However the message in the app notification was different to when I did not have a charge window and departure configured.
Without the window the app says charging has started and gives me an estimated completion time.
With the window the app says charging has started and “charge in time slot mode is active”. This is instead of a predicted end time. Even though in this case the predicted end time that would have appeared is comfortably (by hours) within the window.

The second point is that it charged the car to 100% at the normal rate in the normal amount of time.
It finished many hours before departure time.

30 minutes before I was due to leave I checked the EVSE and no further activity was happening.
At some point after that, maybe 10 mins before departure time, I can’t be sure, it started to pull down 2.5kW.
When I went to the car a minute or two before departure time the gauge cluster said the battery was at 99% and charging would be complete several minutes later. I unplugged the car regardless and the display said the battery was 100% full…

I need an OBD2 scanner to verify this but what I think is going on is:

1. The car does not delay charging to ensure a pre-conditioned battery by departure time.
2. It does not use electrical power from the wall to heat the battery in any way.
3. If the comfort climate is set to ensure a warm cabin for departure time it uses the heat pump, which pulls up to 2.kW to heat it. If you live in an even colder environment it may supplement with resistive heating thus you will see a greater power draw. When I did this the car was in the garage and a few degrees above freezing so I saw 2.7kW on my EVSE which would be the 2.5kW heat pump plus charger losses.
4. I don’t believe the car draws the power from the wall to power said heat pump or resistive heater. That would be extra wiring and redirection that would not be justified. I believe it pulls the power from the battery just as it does when you’re driving and the charger sees the drop in battery level and charges it at the same time. 2.5kW leaves the battery and 2.5kW enters the battery. This would explain the 99% batt level display while it was heating the cabin (which is probably super close to 100 give it take based on voltage sag or not).

This movement of energy in and out of the battery will give some level of pre-conditioning, not much. If the car is in a very cold place then it’s also using resistive heating to it will move more energy in and out of the battery causing it to warm a little more. But in the grand scheme of things it’s not much and that is probably why in very cold places you still lose your power bars as the battery isn’t even close to warm enough from this activity, albeit slightly better than nothing. At some temperature it might make the difference between losing a bar or not.
This also tallies with what BMW/Mini say, or rather what they don’t say. They don’t say the battery can precondition.

Thats my current belief anyway.

 

[Puppethead]

Here's my charging session this morning. As you can see, my charge window is 21:00-07:30. It did start when I plugged in at 18:14 because I forgot I was in charge immediate mode. After I changed to charge in window it paused. This morning when I checked it was still charging, having started the charge at 02:51. It completed the charge at 06:45.

 

[AndysComputer]

Interesting…

that is not how mine behaved.
It started charging immediately the slot was open and finished within 45mins.
But the car was warmed up inside ready for departure time of 4:59am.
So something very strange is going on as the cars are seemingly behaving differently…




It says "plugged in" but what it means is the EVSE woke up at that time as it has its own 8:00pm to 5:00am window as I normally have the Mini set to charge immediately and just added a charge window to that for this experiment.