Balancing a prepackaged LFP battery that I don't think has a balancing BMS

Picked up a Weize 6AH LiFePO4 12V battery to use with my QRP ham transceiver. Charged it with a bench supply set to 14.6V with the current set at 2A max. Noticed the current draw is dropping to zero when the battery loaded supply was about 14.06V. To me this means one of the cells internally reached the upper limit for the BMS before the whole pack got to 14.6V.

So I'm thinking this pack doesn't have a balancing BMS. How best should I use this pack to not increase the imbalance between cells? Is there a way to get the cells in better balance without cracking the case open and either replacing the BMS or manually balancing the cells?

Thanks

Set up a charge voltage at 13.9 volts. It's probable the BMS has a balance function, usually this is set to function under charge once the cell volts exceed 3.4 volts. Hopefully overtime the cells will get more in balance and you can increase the charge volts.
It's very unlikely you will ever get a balanced battery at 14.6 volts.
There is little to be gained charging at high volts, 14.0 or 14.2 volts is more than enough.

Without knowing the BMS parameters it hard to tell what's up. The BMS could be cutting out for battery overvoltage rather than cell overvoltage. Sneaking up on a charge with 13.9V is a good idea. A few charge/discharge cycles may even things out.

AlpineJoe said:

I'm thinking this pack doesn't have a balancing BMS

Click to expand...

More likely the passive balancers are working but being overwhelmed with the charging current. It is common for balancers to siphon off tiny amounts of charging current, less than 100mA. It can take many cycles to balance at that rate.

Reducing charging voltage, as @mikefitz wisely suggests, tends to keep radical imbalance from happening in the first place.

This is what I do to get a pack fairly balanced:
1. Discharge your battery a bit (say 13.6v)
2. Set your charger/power supply to 14.6v (or less, but at least 13.9v).
3. Set your PSU current to 100 to 200 miliamps and start charging.

This might take a while, but this slow charging at the top of the battery SOC will allow the BMS to balance the cells, while not letting them charge further.
As mentioned, most passive balancers are only a few 10s of mA per cell. So you need to charge at a rate slower than that to allow a good top balance.

You may need to repeat this procedure a few times, if the BMS still cuts out.
I suppose that once you do this, the cells will be balanced well. As long as you don't discharge or charge at a high C rate, they should stay pretty well balanced (given that they are of moderate quality and matched capacity).

Thanks everyone! I'll perform some low current, low voltage setting charging and see if it helps.