Loosing main battery charge during parking

[Esparza]

Interesting, but is normal for a lithium battery to reduce the voltage a bit after charge. You can test it with a spare cell without bms. For me going from 3.958V to 3.952V is not due to balancing but tempertarure changes and the resting of the cell, is just 6mV. Passive balacing when the battery is not full have no sense as you are not going to win anything.

 

[elm70]

I'm using lithium battery , with manual charging and manual balancing since early 2000 in the RC Car/Airplane/Drone scope

Yes ... after a battery is fully charged, it tent to lose voltage .. but I have not much experience on partial charge of lithium battery ... so I did not notice if there is any voltage reduction in this specific scope ... also normally I'm charging at between 1C to 0.5C level, my hobby batteries .. while the PHEV with car charger get charged at 0.2C level .. which should not rise much the voltage of the cell

Anyhow ... I agree that numbers are not 100% clear ... but some indication are quite relevant:

After usage my car had: 3.802/3.816v .. so 0.014v difference
On the next day , with car parked and unused: 3.847/3.852 ... so only 0.005v difference

I don't believe this difference happen in natural way ... I bet it has been due to balancing.

Same after charging : from 3.958/3.966 to -> 3.952/3.958 .. so from 0.008 down to 0.002 difference

As well .. nobody report to have unbalanced pack ... even for quite aged pack ... for me the car is always balancing the main battery
And balancing with current technology is always about discharging the high voltage cells

Both PHEVwatchDog and EvBatMon report the "Target Voltage per Cell" , which is looking to me to which voltage each cell need to be "aligned" by balancing

 

[Esparza]

I still think its not cause by balancing. Sometimes the Ah increases 1-2 after some ours parked, and that must be software related, so if you loose some Ah maybe its also software.

 

[GreyBigFoot]

From my experience and testing I find there are actually two kinds of balancing procedures used by the PHEV.

My usage involves full charging every day the PHEV leaving in the morning with less than half an hour after charging.

I do 25km to work, leave the car parked there for about 9,5h and by the end of the day I'll do 25km back.

Roughly every once in five the PHEV charges just under 100% of the capacity. Mostly it will charge up to 105-106% of the reported capacity.

When it charges over 100%, I'll lost about 1.5 to 2.5Ah after parking.
When it charges above 100% (which is most of the time) I'll loose nothing or actually gain about 1Ah of charge.

And this is happening every time.
As it will loose rapidly the charge when full, you'll have to measure the readings just after charging, or at least in the next half hour to see it going over 100%.

So with this, I suspect that for the times it charges under 100% it has done a balanced charging, targeting the estimated capacity of the pack.
For all other times it has just charged with no balancing involved, which explains why it is going over 6% of the estimated capacity of the pack.

After arriving at work if I check the min/max and target cell's voltage, target value is always under min value.
When getting back to the car after the 9,5h parking, target is always between min and max value.

Which I think is due to passive balancing from the CMU while parking.

Effectively I won't see differences in EV range, since it's leaving home with an extra 6% and loose those later, or don't loose anything/gain a little.

Still, not the smartest way of dealing with a battery if you'll ask me.