Battery degradation driven by aging, charge cycles and charge current

[jadnashuanh]

If you did tick the preconditioning box as well, the battery should have been warmed up to 10-11C. The system just won't warm it any further (at least according to my observations), so the temperature gain may depend on your starting temperature as well.

Preconditioning on the check box is related to the cabin. Setting a departure time is what warms the battery.

 

[Oleksiy]

You mean the car always preconditions the battery whenever a departure time is set? I'll test this in spring once my car is charged outside and I could monitor the current draw via my OpenEVSE. I charge using my OUC in the garage now, and the power meter is too far away from my house to check the draw.

My understanding was that the battery warm-up / cool down was launched if the preconditioning box is ticked (which works in the conjunction with the departure time only anyways), and also in case the car is plugged in. When not plugged in, the car will precondition just the cabin. But again, I got this understanding from here https://insideevs.com/bmw-i3-preconditioning-works/, the owner's manual is notoriously silent on the subject, or I may have failed to find the relevant info.

 

[Kristian]

Battery preconditioning only works with a set departure time and the car is plugged into a charger. Cabin heating will still trigger even if the car is not plugged into a charger.
Supposedly for battery preconditioning to work the the departure time needs to be at least 3 hours in the future. By using a physical timer on the trickle charger socket and only giving power 2 hours before the set departure time I've managed to get some battery heating. Today I want to go out in a couple of hours. If I set the departure time for 2 hours time will it warm the batteries or will the car decide that 2 hours is not enough time and not bother at all?

 

[Oleksiy]

I believe it may depend on the available kW capacity of your charger.

 

[Kristian]

I believe it may depend on the available kW capacity of your charger.

That as well - 2kw cabin heater and 1kw battery heater from a 2.4kw charger!
If only there was a button to just warm the battery or prioritise one requirement over another.

 

[Oleksiy]

Hmm... I wonder how my car was able to pull 5.5 kW while preconditioning and at 100% SOC if the heaters were only 3 kW together. That's based on the graph provided by OpenEVSE charger.

Anyway, you could always verify if it does attempt to pre-heat the battery by checking the before and after temperature of the pack (it may warm up a bit due to the charging itself though, so the experiment would show more if you start the pre-heating at 100% SOC). I wish we had a more convenient way to do it though. Like Leaf owners do.

 

[Kristian]

Hmm... I wonder how my car was able to pull 5.5 kW while preconditioning and at 100% SOC if the heaters were only 3 kW together. That's based on the graph provided by OpenEVSE charger.

Anyway, you could always verify if it does attempt to pre-heat the battery by checking the before and after temperature of the pack (it may warm up a bit due to the charging itself though, so the experiment would show more if you start the pre-heating at 100% SOC). I wish we had a more convenient way to do it though. Like Leaf owners do.

You are right - Just checked in the book by David Bricknell - cabin heater can do 5kw bursts for short periods when very cold which will be drawn from the battery if I'm using my trickle charger.

 

[jadnashuanh]

The battery heating element is a 1Kw device. Depending on whether you have a BEV or a REx, if it's cold enough, both may use resistance heaters to warm the cabin, but that's the only way the REx can provide cabin heating. The heat pump, if it's not too cold is far more efficient.

So, other than the secondary heating of the batteries when you're charging them, the only way to request them to be heated while plugged in is to set a departure time. During that, cabin preconditioning is optional. You can request immediate cabin preconditioning even if not plugged in, and, if you're not plugged in and set a departure time, since it won't warm the batteries unless plugged in, you could delay the cabin preconditioning, so you do have some flexibility as currently implemented. While it may not be all that clear, that's what's happening.

To get full effect, the OUC won't cut it...you need a larger capacity EVSE. While the car will try, you will NOT leave with full battery capacity unless the EVSE is large enough when you select a departure time and cabin preconditioning unless the temperatures are fairly mild. You'll get a bit more range with the BEV, because of its multiplier effect at outputting heat verses the REx's resistance heating. I've seen my EVSE pulling more than 20A while in the cabin preconditioning phase of a departure time function. A 12A EVSE won't cut it and let you leave with a full battery, but, your total range available will still probably be better than if you didn't when it's cold out.