BMW 330e pack balancing

[FFMan]

I've finally got the BMS on the front pack restored to working order, and one pack of the 6 is 150mv per cell higher across all cells than the others.

I've verified the accuracy of the reading by swapping the bms module and i'm comfortable that it's correct, but i will check with a meter.

I have a version of simpbms code running on a teensy and it says its balancing but i don't think anything is happening.

Is this code known to activate balancing OK on the BMW packs ?

[royhen99]

Simpbms code balances BMW phev packs. The rate is very slow, maybe only 2mV per hour so a 150mV imbalance could take 2 - 3 days to balance.

[FFMan]

ok thats good to know.

The balance timer is running. Should the balstat numbers against each module register anything or does it just do its thing quietly ?

[royhen99]

balstat indicates which individual cells are being balanced. 1 balancing, 0 not balancing. It's one digit per cell so 0xFFFF is all 16 cells in a module balancing.

[FFMan]

thanks for that. I have my settings set to:-

and my output showing:-

which if i read it right is no balancing going on.

Should this work as configured ?

[FFMan]

i note the 'Series cells fault' note, but I can't at the moment understand what is causing that to appear as I have series cells set correctly to 16.

[royhen99]

Cells in series per string should be 96.

[FFMan]

Great - that started in balancing if i read the output below correctly.

I note it cycles balance on/balance off every minute or so. Is this intentional to let modules cool or something. Could i increase the duration here ? The modules are warm to the touch, but not hot.

I've set a low balance point so most cells are discharging, and it looks like it going to take some time, but now i know it works i can at least reinstall in car and balance as and when time permits.

[royhen99]

Cell voltage readings are only valid when not balancing so they are updated every minute. The min to max cell voltage difference is checked against the "Balance Voltage Hysteresis" setting and balancing cycle continues until this is met.

[FFMan]

thanks - i was just looking at the code and i see what you are saying.

It is actually balancing for 2 minutes, then waiting for two minutes, makes sense as you approach the cutoff but I have a long way to go, so i was wondering about altering those timers, at least whilst i'm so far off but i don't want to over-stress the discharge components.

[tom91]

thanks - i was just looking at the code and i see what you are saying.

It is actually balancing for 2 minutes, then waiting for two minutes, makes sense as you approach the cutoff but I have a long way to go, so i was wondering about altering those timers, at least whilst i'm so far off but i don't want to over-stress the discharge components.

Do what ever you want, please note you want the readings to stabilise and give the balancing circuits a time to cool down. Altering the timing can effect both of these causing unpredictable balancing behaviour.

@royhen99 - thanks for answering the questions regarding the SimpBMS.

In this case I would manual balance the modules using a 70V power supply.

[FFMan]

thank you all for the help - now i understand the capability and options i'll work something out, and then keep on top of it better

appreciate all the help

[FFMan]

So in the end i modified the code to do 12mins of discharge, followed by 30 secs of rest time and this ate into the delta much more quickly, though it still took a few days.

From the temps i can't see a need for a rest period but I'm sure there was a good reason. However i think i 'll modify the code to stay in discharge mode until balstat for each module is zero which indicates balancing is complete.

thanks for the help