Balancing multiple batteries in parallel

[bds70]

What's the best way to maintain balance and soc between 4 320ah 12v batteries wired in parallel. The cells will have all been top balanced correctly prior to creating each battery.

One of the recurring problems I had with the commercial batteries that have basically proven unsuitable, was maintaining the same soc but frequently finding one being much lower than the others.

So is there an efficient way to keep all batteries balanced?

 

[upnorthandpersonal]

If they are connected properly with same length cable and good connections, they should keep themselves in balance and you don't have to do anything (even with different capacities). Are you sure the state-of-charge indication is correct?

 

[shvm]

If they are connected properly with same length cable and good connections, they should keep themselves in balance and you don't have to do anything (even with different capacities). Are you sure the state-of-charge indication is correct?

Precisely.

You shouldn't depend on SOC to judge balance of the batteries. Rather voltage after a full charge. And discharge.

 

[bds70]

If they are connected properly with same length cable and good connections, they should keep themselves in balance and you don't have to do anything (even with different capacities). Are you sure the state-of-charge indication is correct?

It was, but as I said, from the get go, these batteries were a flop. I have just finalised a settlement with them for 95% refund as they are not (under Aussie trading law 'fit for purpose') so much of the problem I may never see again.

I thought I would ask in case there were any tips n tricks.

Thanks for taking the time to respond

 

[bds70]

Precisely.

You shouldn't depend on SOC to judge balance of the batteries. Rather voltage after a full charge. And discharge.

Agreed and hopefully once I build my new batteries that will b the case.

Thanks for taking the time to respond

 

[upnorthandpersonal]

It was, but as I said, from the get go, these batteries were a flop. I have just finalised a settlement with them for 95% refund as they are not (under Aussie trading law 'fit for purpose') so much of the problem I may never see again.

Yeah, might have missed or forgotten that.

You could still salvage the cells (if they're prismatic). Otherwise, if these batteries are defective, no matter the amount of balancing you would do would just lead to lost energy.

 

[740GLE]

What BMS is in these batteries?

Some have found swapping out poor BMS for a quality one is a solution. Others have added active balancers.

Sounds like you got more your money back so I’d say hack into them.

 

[bds70]

What BMS is in these batteries?

Some have found swapping out poor BMS for a quality one is a solution. Others have added active balancers.

Sounds like you got more your money back so I’d say hack into them.

I was hoping that might b the case, but unfortunately the company insists the batteries are returned in original condition.
Despite their claims I now believe the cells were probably B grade. Which would explain why they are the cheapest lifepo4 in Australia by a fair margin.

 

[squowse]

What's the best way to maintain balance and soc between 4 320ah 12v batteries wired in parallel. The cells will have all been top balanced correctly prior to creating each battery.

One of the recurring problems I had with the commercial batteries that have basically proven unsuitable, was maintaining the same soc but frequently finding one being much lower than the others.

So is there an efficient way to keep all batteries balanced?

The problem is different internal resistance of the cells. So one battery will drop voltage under load more than another and give less current compared to the stronger one (with less internal resistance). They can also have different SoC/voltage curves even with no current flowing.

 

[bds70]

The problem is different internal resistance of the cells. So one battery will drop voltage under load more than another and give less current compared to the stronger one (with less internal resistance). They can also have different SoC/voltage curves even with no current flowing.

Is there an answer to the internal resistance issue,?

 

[bds70]

What BMS is in these batteries?

Some have found swapping out poor BMS for a quality one is a solution. Others have added active balancers.

Sounds like you got more your money back so I’d say hack into them.

Hmmmm. When I am researching new stuff and get tired, my head explodes at night with strange & wonderful ideas. 'some' of them turn out to be good, the majority just dumb. LoL

Anyway last night I suddenly thought, is it possible to have 4 12v batteries in parallel, but 1 16s BMS attached to all the individual cells? (Or maybe 2 8s, because of the amp draw being high in a 12v scenario)

Smart or dumb? And why?

 

[740GLE]

The BMS has the current flowing through the string of cells. It can only interrupt one string.

Bad things will happen if you try what your proposing.