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Balance on Series connected string


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Hi Guys,

I am getting a weird issue after running fine for a few weeks.

My 3rd and 4th battery in series from positive side are becoming unbalanced.

I noticed that the 3rd batt was always around 0.5v lower than the rest, and could see it cause issues as it drained much faster, but would pick up quickly aswell, causing the whole setup to switch between grid and battery modes a few times a day.

I changed the batteries (3rd/4th) which we're the lowest, with new ones on Saturday. Made sure the SOC was close across all 4 batts. And hooked it up.

It was much better, as it ran most of the day off Batt mode, until it kicked back to grid at 48v. I thought it good to recharge from grid overnight to 54v then.

They we're happy and at 54v and around 13.5v each on Sunday morning.

I switched back to SBU mode, and immediately battery mode, with a little input from solar as it was still early. This drained the batts to 48v again over 2 hours.

I charge solely off Solar from here on out, but noticed it only charged for 10mins, before kicking back to batts off 58.8v.

Load was 1.5kw average (washing day), Solar 900-1200w, and batts drainging between 5-10amps.

It would only be able to sustain the load for 20mins, and then charge 10mins, rinse and repeat. That is definitely not enough time to chage

3 cycles before 12pm, and the batts are way out of sync again.

1. 13,7v

2. 14.5v

3v 12.5v

4. 12.5v

So it's back to the drawing board, as the new batts are now behaving similarly. I swopped the front pair and the back pair, and withing 2-3 cycles, it would again change the charge around.

Front pair high, and back pair low.

I don't have a BMV yet, so I went according to the good old manual multi-meter, writing down the readings every few minutes.

Any ideas?












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Voltage is a poor measure of state of charge. The lower voltage on the new ones mean nothing. Often a dead battery shows a very healthy voltage until you try to do something with it, while a good battery might show a lower starting voltage (12.8V even) and stay there when tasked with some work. So unfortunately none of this means anything... other than that you mixed batteries of different ages and have now ended up with an imbalance, which is entirely to be expected.

Forget the BMV for now. Get a battery balancer. I have mixed feelings about the HA02 at the moment, some recent results (Gabriel's string that went out of wack despite having them in, and another result showing very low balancing currents, much less than advertised) make me wonder if they are as good as I used to think. Only trouble is the alternative is three Victron balancers and they cost around 1k a pop. Nevertheless, you cannot run batteries of different ages without a good balancer.

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Thanks, That's the main reason for swapping the 2 older ones this weekend. So I have 4 fresh ones on the string now.

I have read a few posts around that indicate similar issues with the all-in-one.

School fees i suppose :)

But with the money I spent and all the forum help, I should graduate soon.

Any preferred provider for that balancer?







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