Battery discharge

[Julianna]

I have a battery bank set up of 4 100ah LIFEPO4 batteries hooked up in both series and parallel to make a 24v system, when I hooked them up I tried to have them all pretty close to the same charge, but as time goes on they keep getting further and further from each other. The ones that are being depleted the most are the ones that have the wire coming from its terminal to the Growatt AIO system. This is my first time working with solar or electricity so my basis of knowledge is limited, and I'm not sure what it could be, any information is appreciated.

 

[rmaddy]

Two things.

First, you need to separately charge each battery to 100% SOC. Do not base it on voltage. If they don't all start out at the same SOC they will never be balanced.

Second, you need to ensure you are wiring the batteries correctly to help keep them balanced. Take two batteries and connect them in series. Do the same with the other two batteries. Make sure the 2 series connection wires are the same length. Now wire the two series strings together in parallel. Those two wires do not need to be the same length since one is negative and one is positive. Now connect your battery bank to your system. You must connect the system to the correct batteries. Connect the positive system wire to one battery. Now connect the negative system wire to the opposite battery of the other string. This is important for proper balance.

Do not connect both system wires to one battery. Do not connect both system wires to the batteries of just one series string. Do not connect both system wires to the batteries on the same side of the parallel strings.

Connect the system wires on opposite corners so the two are on different series strings and on the opposite side of each string.

 

[joanna_lannie]

The battery is probably not balanced. It seems that you have performed the initial balancing of the battery, but there is no follow-up. This situation can be solved by balancing the battery. If you don't mind the trouble, you can choose manual balancing, but this means that you need to operate the battery every once in a while. ; but if you want to save a little, a balancer is recommended, but it will cost you some money. Of course you can also just rely on the balance function of the BMS, but this is only a minimum balance. So it mainly depends on your thoughts.

 

[Hedges]

Make sure the 2 series connection wires are the same length. Now wire the two series strings together in parallel. Those two wires do not need to be the same length since one is negative and one is positive. Now connect your battery bank to your system. You must connect the system to the correct batteries. Connect the positive system wire to one battery. Now connect the negative system wire to the opposite battery of the other string. This is important for proper balance.

I think those two do need to be same length (the two stitching positive to positive, and negative to negative). Because current to one string goes through one wire, and to other string through other wire.

"Connect the positive system wire to one battery. Now connect the negative system wire to the opposite battery of the other string. This is important for proper balance."

Agreed, and it is these two wires that don't need to be same length. Because current to both strings goes through both of them.