A gift horse.... how to match Calb 180ah LeFePo4 cells

[CapnGil]

A gift horse... best method to match used LiFePo4 Calb 180ah cells?

Summary; I was gifted 46 Calb 180ah cells that came off a dock yacht; owner upgraded to entire Victron package. My vessel runs on 24v, so I set them up in 8s5p (using 40 cells) with each bank having its own Daly 200a BMS. They are charged by six 285w solar panels in 3s2p configuration, feeding a Growatt 3000w hybrid solar charger. The cells were given to me individually so I initially did a mid charge to 3.3v each and parallel connected all of them for two days to equalize them and then matched them up by internal resistance: I thought it was a good way to match them.
However, after a few days the voltage have strayed between cells by more than .2 volts.

So my questions are as follows:

1. What would be the best way/method/procedure to match up these cells in groups of 8? Top balancing, bottom balancing, capacity testing (thats gonna take a while), etc....

2. Upon doing so, how could I manage/maintain the voltage between battery banks, once matching of individual cells are done?

Any suggestions would greatly be appreciated.

Be well
Gil

 

[sunshine_eggo]

A gift horse... best method to match used LiFePo4 Calb 180ah cells?

Summary; I was gifted 46 Calb 180ah cells that came off a dock yacht; owner upgraded to entire Victron package. My vessel runs on 24v, so I set them up in 8s5p (using 40 cells) with each bank having its own Daly 200a BMS. They are charged by six 285w solar panels in 3s2p configuration, feeding a Growatt 3000w hybrid solar charger. The cells were given to me individually so I initially did a mid charge to 3.3v each and parallel connected all of them for two days to equalize them

This does absolutely nothing except equalize voltage. It actually masks issues that might be detected due to voltage loss of weak cells.

and then matched them up by internal resistance: I thought it was a good way to match them.

Better than nothing or random.

However, after a few days the voltage have strayed between cells by more than .2 volts.

Because they weren't balanced.

So my questions are as follows:

1. What would be the best way/method/procedure to match up these cells in groups of 8? Top balancing, bottom balancing, capacity testing (thats gonna take a while), etc....

The ONLY way to actually match them is to test all 40 cells. High effort, low reward unless you have major outliers.

You've matched on IR, so just top balance each battery individually.

Charge all 5 to full until BMS trips, break one out, charge each individual cell to 3.65. Rinse and repeat.

2. Upon doing so, how could I manage/maintain the voltage between battery banks, once matching of individual cells are done?

After each charge/load each battery to within 0.2V of each other then parallel. The individual BMSs will manage the cells, and the parallel connections will keep them the same total voltage. Important with so many batteries in parallel that they be connected properly.

See Victron's Wiring Unlimited in Resources.