Bms issue or not?

[Greg5972]

I just finished building a 72 volt 24s headway pack using 40152s Cells. I have a BMS with part# PCM-L24S60-622. According to my Alloy Shell 1200watt charger the batteries are charged. The charger is now at the balancing stage. I am new too this and am uncertain of a few details about this process. My main concern is that I can see some cells (with charger on) reaching 3.9 volts. With the charger off they are at about 3.80volts. The majority of the remaining cells are anywhere from 3.42 volts to 3.63 volts. It has only been balancing for about an hour. I have since unplugged the charger until I get confirmation that these voltages are ok. Any info would be appreciated.

Thanks,

Greg5972
Trek 3500
Crystalyte 3540
24s 15ah Headway.

 

[dnmun]

did you balance the cells before you wired them in series?

without a picture of your BMS there is no way to know which one you have.

3.9V is normal for the HVC on lifepo4 BMSs.

the charge is turned back on when the cell drops to 3.8V on most BMSs.

it just takes a long time to make it balance when it starts out unbalanced.

 

[999zip999]

The 3.45v one could use a single charger on the low cell, but if it dosn't stop at 3.65v. I wouldn't use one. Because everyone walks away and forgets. On the new battery.
Or take 12v car brake light to help bleed down the high cell. Or just let the bms bleed it down. 3.45v is pretty full like 82% maybe. Where did you buy the bms ?
I guess you didn't parelle all the cells first and charge to 3.6v for balance.
I would do a couple light cycles and time on the charger for balancing and don't try and find the bottom. The 1200 watt charger throws a lot at it making it harder to balance. Light cycles after balance.
Don't let the cells go above 3.9v. because after 3.6v they run for the sky.
Why not take it off the charger and let the bms bleed it down it should bleed down to 3.6v on the high cells with time.
I would put 4- 6s sense wires on it for easy checking and balance with a small 6s charger or one of hyena's bc168 balanace charger thru the extra set of sense wires. Or.

 

[Greg5972]

Thanks for the replies,

No, I didn't balance the cells prior to assembly. I have a hobby charger that does lifep04. I think I will charge the low cells with that. I attached a picture of the BMS. How long would it normally take for the cells to balance?

 

[dnmun]

sometimes it takes days and days.

 

[dogman dan]

Yep, an hour won't balance a pack that is very far out of balance. Cool that you have the RC charger, perfect for bringing up those lower cells, or bringing down the high ones one by one, or two or three at a time if they happen to be two in a row both high or both low.

I'd break out the charger and bring up the low ones, then put it back on the regular charger overnight.

As my pingbattery was in it's last few months, I added some parallel jst plugs to the balance wires. Now able to watch the bms working with a cellog 8, I was quite amazed to see how high a cell could get while the bms worked. 4v for a lifepo4 cell is pretty high, but I was seeing it all the time. Soon after, I'd see the bms bleed it back down, but once that charger turned on again, it would bounce back to 4v immediately.

This was a tired old pack, so I don't know if that was normal or not, but I was pretty surprised to se 4v.

 

[999zip999]

Getting voltage in a cell seams weird as how much and how fast you push it and how fast it will take it. Some old cells you push volts, amps at it and it can't hold it and some old cells just over fill like a rocket. It seams in most lifepo4 packs there is some cell that has alittle differents. Still 3.4v is close to full. Or end of charge.

 

[Greg5972]

Ok brought some of the lower cells up with my other charger. Left main charger on overnight and now all cells are within .05 of each other. As suggested I will give the pack some light cycles and hopefully it will get even closer.

Thanks,

Greg

 

[dnmun]

you can just leave it on the charger but .05 is as close as they will get imo.