question

@nigelb100

Your wiring has to be balanced for the same discharge or perfect current sharing from all batteries. Almost impossible with a 48v bank made from 4 x 12v batteries.

The end ones will discharge and charge faster - OHMS law. See the book wiring unlimited for more information.

Did you do an initial full charge of each individual one before install? What happens when they have not had a good initial charge is you get cell imbalances. and battery imbalances. With a 48v system you should also look at getting battery balancers. (also covered in the book)

What dimension are your DC links between each battery? I find people tend to under-size and it makes bank balancing worse.

You could try hold them for over a day at 100% to see if they do balance out a bit, then try your discharge again. But really each one should be individually charged.

Thanks for the answers.

Yes, batteries were charged individually before installation as per instructions using a Victron charger prior to putting them into the power pack so I don't' see that as the issue.

Stefanie - the BMS is a Victron VE.Bus BMS hooked up to the inverter.

It is a simple set-up: four batteries wired in series. The positive of the inverter is connected to battery one and the negative of the shunt is connected to battery four. The other side of the shunt then goes to the negative of the inverter.

I can see the SoC of each battery using the Victron Connect App. I have had the inverter plugged into the power overnight to see if it balances out. Coming in this morning what I can see now is:

BMS red light is on.

The issue seems to be with battery three. Looking at the Victron App this battery is much too hot and is overcharged (probably why the BMS red light is on).

Readings for each battery as follows:-

Battery one (positive to inverter) - "Ready for use". 13.21V/17 degree C/Balanced. Each cell roughly 3.30V

Battery two - "Ready for use". 13.21V/18 degree C/Balanced. Again each cell roughly 3.30V

Battery three - "Ready for use". "Charging disabled". 14.34V/32 degree C/Balanced/ Each cell roughly 3.57V

I have a spare battery and this was previously installed in battery position three with the same issues.

I subsequently charged this battery using a Victron charger and it behaved correctly.

Alexandra - I had a battery balancer in the system in the past but I took it out as I thought with the BMS & the battery BTV system it wasn't needed.

Size of the cables might be something worth looking at....I think they are 50mm

Thanks again both..

Well In would think that the batteries are NOT balanced and may have NOT been balanced at the start, all cells have to be at 3.65v to be balanced. . all batteries should be the same voltage.

when connected in series the same amount of amps is taken from ALL batteries, at ALL times

to fix this you have a few options

1. leave the system on bulk charge for as LONG as it takes for the other 3 batteries to raise to the same voltage as battery 3 (make sure that NO cell goes over 3.65 volts ) if you choose this option slowly increase the charge voltage to 56 volts and set the bluk and float to the same voltage until balancing is finished - once there slowly raise it to 58.4 to get all cells to 3.65v in all batteries. then return to normal charge level of max 56volts bulk and 54 float or the normal lithium setting and ( NOTE they will get hot - well the cell balancers inside will so having a fan blowing through the cooling slots would be helpfull) its not the batteries getting hot its the cell balancers. Doing this option depending on how unbalanced they are - this could take a LONG time even 1 month or longer without doing any discharging..

2. take all batteries OFF line and charge one at a time so that ALL cells are at 3.5 volts or 14. volts in the balancing process some cells may rise to a higher voltage, (do not go over 3.65v) in each and then all batteries you must do the same - then and only then reconnect them in series and bring the system back online ( this would be my preferred option.)

of note bring all cells to 3.5 volts - then once they are all at 3.5v on each battery - slowly raise the battery voltage until all cells are at 3.65 volts 14.6volts (again do not let any cell go over 3.65 volts)

once you do this the battery will then be in balance.

there are many ways to do this balancing but the main area is do not go over 3.65 volts on any one cell.

of note the cell starts being balanced at 3.5 volts and then the cell balances inside will get warm to hot.

Thankyou very much Paul....I'll try it out

I set the battery charger so it charged each cell on my spare battery to 3.65V and it has now settled back down to 3 cells @ 3.63V and one @ 3.64V (14.53V). I guess this is optimal now so I just need to do the other three.