Departure Time, Battery precon and off-peak charging

[psquare]

I've just read again through Tom M's great post on "How preconditioning works".

Temperatures are currently high enough here in the UK to not precondition the battery in the morning. However we do use the off-peak charging almost every night and I have noticed the last few mornings that about 1h before departure time the car was back at 96%, although I am sure the charge must have been completed on 100% earlier in the night. It seems the car is performing a battery precon.

The settings are as follows:

Departure time: 8:15am
Preconditioning: Off
Off-peak charging: 2:00am - 8:15am

The last 2 nights I plugged the car in with around 50-55% charge left, which should easily be recharged within 2-2.5h, which means the car should have completed charging at 4:30-5am. However, as I mentioned above, at 7:15am the car was charging and SOC at 96%.

Have I misunderstood something? Or is there a setting in the car menu that the app can't influence?

 

[LMOR]

Tom's description might be correct for US and 110V standard charger, but it is not correct for an European car.
The precondition selection only affects the cabin. Preconditioning the battery is linked to departure time.
The statement that it is only working if you set it 3 hours before is also not true.
I have a lot of measurements around this. Preconditioning the battery at around 2-6 degrees, Celsius uses around 1+kWh, or 5-6%. Around 8-12 (night temperature), less the than 1kWh.

 

[janner]

LMOR - Can you give us a similar pre-condition procedure for outside of the USA?

 

[LMOR]

What do you want to know?

It simple. Select departure time to precondition the battery. It is a good advise to do it more than 3 hours before, but the car will anyway do it's best.
It needs to be connected to precondition the battery, and the more Ampers the better. (Less effect drawn from battery. At 12A normally the first cycle is drawn directly from the wall, and the 2 next/last ones, drawn from the battery, and then it is recharged. Last one normally recharged before cabin precondition starts)

Preconditioning the cabin, will happen around 20-15 minutes before departure time if selected or activated through the app or remote.

 

[jadnashuanh]

Once the battery reaches 100%, the car doesn't turn the EVSE back on until the percentage drops at least a few percentage points. Now, if you've set a departure time, preconditioning the cabin (if you've checked that box) and the battery pack will drop it enough to cause it to recharge. If you depart earlier than the programmed time, it might not get back up to 100%, and if it needs to (depends on the temperatures of all bits involved), it may do that outside of your low-cost window.

 

[barrychan]

Do we need to select the temperature for it to precon?

 

[Sparky]

No, the temperature is fixed at something around 72F.

 

[Jeffj]

The cabin always pre-conditions to 72F degrees, whether that requires heat or cooling. You can't adjust that setting.

The battery pre-conditioning brings the batteries into the "optimal" operating temperature range. I believe that BMW states the optimal range is 77F to ~100F. There is not an easy way to tell what temperature the batteries are at. You can see this by activating the hidden service menu, but that'd difficult to do while driving (requires holding the trip computer reset button down for 10 seconds to activate menu, then entering a code to expose the hidden portions of the menu. The option to show battery temp is 14.05

 

[LMOR]

The battery is heated to 10 degrees Celcius. Above that it only "conditions" the battery. I have not yet measured when pre-cooling starts.
When you drive, the temperature rises, and the highest I got was during a day with between +3 and +8 degrees outside, pre-heated to +10, and then at the end of the day driving upwards, I reached +27 degrees Celsius. Then its clear that pre-heating to optimal temperature around +22, would reduce range because you would need to cool the battery instead.

 

[RJSATLBA]

Returning to psquare's question, I use the off-peak functionality to try and get as much charging as possible whilst my solar panels are active, so at the moment my off-peak setting is 8am to 4pm. What I sometimes see is that it doesn't start charging at 8am but waits and starts at a time that will have the car fully charged at 4pm, which happens to be both the end of my 'off-peak' and also the earliest of my daily departure time settings. So what the OP may be seeing is the same, off-peak charging starting later than the start of the window if the car doesn't need the whole window to achieve a full charge, with the charge slowing right down as the departure time approaches.

In my scenario this may not be what I want, especially if the weather is sunny at the start of my 'off-peak' window but likely to deteriorate, in which case I have to use iRemote to switch to 'Charge Immediately'.

 

[psquare]

Thanks, RJSATLBA. I had actually contemplated the same idea as I haven't been able to check at night when the charging starts. If this is the case then I do question the logic behind it. As it means that cars are left with less than 100% charge if you have to leave earlier.

I've also had a think about the general link between Departure Time and Off Peak charging and it is actually not that clear to me. In fact, I think it should be kept separate. Why not have 2 different settings for both?

 

[LMOR]

So why do you not set 2 departure times. One 1 hour before end of off-peak, and one at departure time. Then you will also use less energy the second time, and then limit the risk of leaving with less than 100%.

 

[psquare]

So why do you not set 2 departure times. One 1 hour before end of off-peak, and one at departure time. Then you will also use less energy the second time, and then limit the risk of leaving with less than 100%.

Yes, I guess this could work, but is workaround at best. Why combine 2 bits of functionality (precon and off peak charging), which aren't really linked?

 

[LMOR]

I am not convinced that they are linked, more than it needs to know when you will be leaving to optimize the charging, because you might need to start charging before the off-peak window. But all these things would work better at 32A.
You could make sure that you charge inside the off-peak period, and precondition will draw directly from the wall.