Balancing Battle Born batteries in a 24 volt system

I have a 24 volt 3000 watt Growatt all in one inverter and 4 Battle Born batteries wired in a 24 volt configuration (2 groupings of 2 BB 12 volt batteries wired in series to create 24 volts.) The positive and negative cables from each 24 volt grouping are connected at a buss bar, then a 200 amp circuit breaker in the positive lead going to the inverter.

My problem is that 2 of the batteries (one in each 24 volt grouping) drain down to a very low voltage, which drains down the other batteries. This happens overnight when only a refrigerator( 1.5 KWH per day) is drawing power. I had a low voltage condition at the end of last year and Battle Born advised me to charge each battery separately to maximum voltage then reinstall the batteries. I was also advised to rotate the batteries periodically to help keep the battery voltages balanced. When I contacted Watts 24/7 (the seller of the Growatt inverter) I was told that I need to install battery balancers, but Battle Born said that was not necessary.

I think I do need to install balancers, but I don't know how to balance 4 batteries in this 24 volt 2 battery per grouping configuration. It seems to me that since I have 2 cables from each 24 volt grouping that are connected to the same buss bar, that should balance the two 24 volt groupings, and that seems to be happening. When I had the batteries fully charged with solar I had a 27.4 volt reading on the Growatt and 27.4 volt reading at the buss bar, and 27 4 volt reading at the 24 volt battery terminals. However, I did have an imbalance in voltage when I measured the voltage on each 12 volt battery individually: 24 volt grouping #1 - 13.24 volts and 14.13 volts, 24 volt grouping #2 - 13.25 volts and 14.11 volts. I am tempted to put the 2 low voltage batteries together in one 24 volt groupings, and put the 2 high voltage batteries together in the other 24 volt grouping.

So my question is: How do I install balancers to keep the individual 12 volt batteries at the same voltage on my 24 volt series system? Any advice you can give is appreciated.

tucsonjwt said:

So my question is: How do I install balancers to keep the individual 12 volt batteries at the same voltage on my 24 volt series system? Any advice you can give is appreciated.

Click to expand...

There are 24V balancers that seek to equalize the voltage between the two 12V. You would need two - one for each 12V+12V string.

Swapping/matching them based on voltage may be wise IF those are real voltages. If one of the batteries is in charge protection mode, it is taken out of the charge circuit, and the measurement across the terminals will be the difference between the total voltage of the charger minus the other battery voltage. You need to turn off the charger/voltage source and/or disconnect it from the 24V string.

IMHO, you may need to parallel all four of them and hold them at 14.2V for an extended period of time.

https://www.amazon.com/iSunergy-Battery-Equalizer-Batteries-Balancer/dp/B09MKN9MQM (these overheat sometimes)

https://www.amazon.com/Victron-BBA000100100-Battery-Balancer/dp/B01DH6B2D2 (this one has issues sometimes)

https://www.ebay.com/itm/175874775173 (haven't used)

(neeya, too expensive for me but seems solid)


HA01 - 1 balancer for 2 - 12v batteries in series (so you would need 2)

red lead to positive on either battery

black lead to negative on the other battery

white lead to where they are series connected

I have two that have worked flawlessly, the batteries stay balanced

I have one that overheated a bit and didn't work, it's replacement works fine

sunshine_eggo said:

IMHO, you may need to parallel all four of them and hold them at 14.2V for an extended period of time

Click to expand...

Yesss..

Thanks for the input. I have all batteries separately charged to 14.4 volts with Victron chargers. To connect all 4 batteries in parallel I will need to create jumper wires between all 4 positive and and all 4 negative battery terminals. What AWG wire size should I use to make those jumpers? It seems that I would have 400 amps total through all 4 wires, although there would be no load draw. I don't want to fry anything, especially myself. Thanks

Can you send us some pictures and details of the setup?

IMO for a 24 votl 3000 watt inverter, batteries should be put in series with 2/0 cable, ant then joined to a common busbar with 2/0 cable and then 4/0 to the inverter.

tucsonjwt said:

Thanks for the input. I have all batteries separately charged to 14.4 volts with Victron chargers. To connect all 4 batteries in parallel I will need to create jumper wires between all 4 positive and and all 4 negative battery terminals.

Click to expand...

Yes. This is easier said then done. What gauge wire would you hook them with? I would not want to use 24 gauge jumper wire.

Might be able to use the cables you've cut already. I parallel cells during top balancing using busbars and I have accumulated enough to be able to do this. I place the positive end on one side, and the negative end on the opposite cell on the other side.

Might be able to get away with one Victron Battery Balancer for a 24 volt bank. Victron has wiring diagams in the manual for using one balancer in a 24 volt bank built with 6 series-parallel 12 volt batteries.

My last question was only in reference to paralleling the 4 batteries temporarily only for the purpose of equalizing the voltage on all 5 batteries. I can't post a picture of my system because I get a message that the file size is too large. I am using 4/0 AWG wire to connect the batteries in 24V configuration, from the batteries to the common busbars, to the 200 amp circuit breaker. I had to go down to 4 AWG from the circuit breaker to the inverter and from the negative busbar to the breaker because the Growatt lugs will not accept a larger size wire.

I am just wondering about rigging up temporary jumpers to hook the 4 batteries temporarily together to equalize the voltage. I have some 6 AWG jumper cables I could cut up to make the jumpers but I don't know if that wire is large enough. Any thoughts?

6 AWG will be good if the cells if the batteries are equally charged.

OK. I will go with the 6 AWG battery cables. Thanks

What current are you charging them with? 30a or less? You could prob use 10awg seeing it’s a temp set up.

Also you dont really need to have all the batteries in parallel and charging (it is easier to set it a forget it), you can always just do one at a time.

The size of cable question was only relating to the parallel wiring of all 4 batteries when they are all fully charged and disconnected from the system. Technically, I have 4 batteries wired in parallel at 100 amp hours each, so it seems that I have a total of 400 amp hours which, from a pure wire size ampacity perspective, would mean 2 ga wire for 4 feet of conductor length, per the table below. With no load on the system other than the minor bleeding of voltage from one battery to the other, I think I am OK with 6 GA wire.


I have already charged each battery separately to 14.4 volts when the Victron 30 amp charger went into float, so I think they are fully charged, but I will check the charge again before I connect them in parallel for disconnected "equalizing." Once I get all of the ring terminals in my hands I will start making the jumpers and test out the plan. Thanks

tucsonjwt said:

The size of cable question was only relating to the parallel wiring of all 4 batteries when they are all fully charged and disconnected from the system. Technically, I have 4 batteries wired in parallel at 100 amp hours each, so it seems that I have a total of 400 amp hours which, from a pure wire size ampacity perspective, would mean 2 ga wire for 4 feet of conductor length, per the table below. With no load on the system other than the minor bleeding of voltage from one battery to the other, I think I am OK with 6 GA wire.

https://www.qualitypowerauto.com/Wire%20Sizing%20Chart%2012V%20DC.htm

I have already charged each battery separately to 14.4 volts when the Victron 30 amp charger went into float, so I think they are fully charged, but I will check the charge again before I connect them in parallel for disconnected "equalizing." Once I get all of the ring terminals in my hands I will start making the jumpers and test out the plan. Thanks

Click to expand...

I used 6 ga wire at first just to balence, using the same charger you have , about any thing 10 ga and up wire will work for thst…on the permanent set up I went a lot larger ..

I did buy a 24v 16a Victron charger for when I went to 2 series wiring ..so as to be able to charge and experiment with stuff without disconnecting the batts ..

Hint….After you get ( 14.4ish) ,Seperate them …remove the float ..see if they hold a close value as they slowly fall over a day or two or three …they should stay pretty close …if not or they act odd then investigate why..

Run em up and run em down too.. cycle em good …especially after ya go to 24 volt.

In parralell you probably won’t have any trouble at all with those batts…

It’s when you switch over to series and 24 volts , and paralleling the 2 pairs , it will get a bit trickier ….

PS… I’m hoping you have a good shunt… you will need it…

J.