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BMW 330e pack balancing
Posted: Fri Apr 12, 2024 8:20 am
by 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 ?
Re: BMW 330e pack balancing
Posted: Fri Apr 12, 2024 9:01 am
by 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.
Re: BMW 330e pack balancing
Posted: Fri Apr 12, 2024 9:48 am
by 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 ?
Re: BMW 330e pack balancing
Posted: Fri Apr 12, 2024 10:08 am
by 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.
Re: BMW 330e pack balancing
Posted: Fri Apr 12, 2024 11:39 am
by 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 ?
Re: BMW 330e pack balancing
Posted: Fri Apr 12, 2024 11:41 am
by 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.
Re: BMW 330e pack balancing
Posted: Fri Apr 12, 2024 11:54 am
by royhen99
Cells in series per string should be 96.
Re: BMW 330e pack balancing
Posted: Fri Apr 12, 2024 12:15 pm
by 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.
Re: BMW 330e pack balancing
Posted: Fri Apr 12, 2024 12:28 pm
by 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.
Re: BMW 330e pack balancing
Posted: Fri Apr 12, 2024 12:35 pm
by 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.
Re: BMW 330e pack balancing
Posted: Fri Apr 12, 2024 1:19 pm
by tom91
FFMan wrote: ↑Fri Apr 12, 2024 12:35 pm
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.
Re: BMW 330e pack balancing
Posted: Fri Apr 12, 2024 1:31 pm
by 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

Re: BMW 330e pack balancing
Posted: Tue Apr 23, 2024 7:03 pm
by 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
Re: BMW 330e pack balancing
Posted: Fri May 03, 2024 11:30 am
by FFMan
Just by way of an update. I dropped the rest period altogether. As I have a gen1 and gen2 pack i did notice the gen1 pack occasionally stops balancing for 30 secs of its own accord and then comes back on plus it takes 50 secs to start balancing whereas the gen2 pack is instant on and stays on.