question

merlepeter avatar image

Victron Battery balancers - do not balance to equal voltages

I purchased 3 Balancers and am using it on a 48V string of 4 x 12 V 170AH batteries. What I find after the balancers have
have stabilsed is that there is almost exactly 100mV difference between each pair of 12 V batteries - so the the voltages are as follows from the negative side 13.65 , 13.55, 13.45 , 13.35 V . The charge current is less than 100mA and all LED are green. The bank is stable and voltages will remain like that for days. The balancers do not appear to balance the voltages to all be equal but rather to achieve a 50mv midpoint error (50mv midpoint error equates to a 100mV difference between two adjacent batteries ) Is this correct behaviour? I have tried each balancer seperately on a pair of batteries and behaviour is the same , the lower batter is always 100mv higher in voltage than the upper battery

Battery Balancer
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6 Answers
Albert de Jongh avatar image
Albert de Jongh answered ·

@merle.peter@gmail.com - did these voltages in your battery bank every change? (Yes, I know this is a very old thread!)

I am just curious, because I am seeing the exact same thing on my 48 volt bank.

Before the balancers were installed the bank would look like this (2x 4 batteries in series):

- 13.77 13.95 13.75 13.47
13.83 13.95 13.71 13.45 +

No midpoint cables were installed before the battery balancers, but now they have been added.

With the balancers running, the voltages look like this:

- 13.84 13.767 13.662 13.541 +
(Because of the midpoint cables the batteries in the parallel strings are of identical voltage)

This looks very much like your example; is it only randomly also from high to low from the negative to positive poles?

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Yes exactly what I get too , I'm not very impressed. Further if your batteries are floating and you then need to use batteries due to a mains failure , the battery voltage obviously drops , this results the the balancers kicking out - which is fine , however the multiplus then recharges batteries again to float level but balancers do not kick in as the threshold voltage is higher than float voltage. You then have to force the voltage up and then drop it again if you want to main float . The design of the balancers really needs to be reviewed and reconsidered

Albert de Jongh avatar image
Albert de Jongh answered ·

Perhaps this was not an issue after all; after a few more days the battery voltages have changed like this: - 13.731 13.705 13.66 13.618 +

It looks as if it is slowly getting better?

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Albert de Jongh avatar image
Albert de Jongh answered ·

@Daniël Boekel (Victron Energy Staff) - don't know if you could perhaps weigh on this? I am just very curious about how the balancers work.

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merlepeter avatar image
merlepeter answered ·

It does not specifically state this on the published product sheet on the internet . Do you have a more detailed spec sheet? Other issues are that if you choose to implement storage mode on the Multiplus then the voltage is too low for the balancers to operate.

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merlepeter avatar image
merlepeter answered ·

It could well be , however the app ( http://bb-demo.victronenergy.com/ ) indicates that the steady state voltage difference is 0V. With the 100mV differences it results a spread of 300mv from top to bottom voltage in a 4 battery 48V system . This is outside the desired range given by the Battery manufacturer stated voltage float range of 13.38V - 13.62V ( 240mv range)

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@merle.peter@gmail.com Thank you for that link to the bb demo. It let me know the balancer is working as intended. I keep seeing 14.10 on top half and 14.25 to 14.29 at the midpoint when I approach full charge. Amps are usually below 6 or 7 on a 600AH bank. I've been worried my top half is not getting enough finish charge or that the bottom half has a bad battery with higher internal resistance and pushing the voltage up.

wkirby avatar image
wkirby answered ·

According to the datasheet there needs to be a 50mV deviation at the midpoint before balancing starts. So yes, I'd say that it is working as designed.

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Yes it does say 50 mV before it starts balancing however it does not specify when it ends. There could well be hysteresis which is not specified

Oh, and it only starts balancing when it's on. It switches on when the battery Voltage is above 27.3V (charging). Is that perhaps your scenario?
So, battery Voltage needs to be more than 27.3V (over a string of two) AND there needs to be 50mV deviation.

Switches on as expected and stays on throughout the float cycle (BTW it switches off during Storage mode - which is another issue I'm not concerned about here ) . Its the steady-state set-point voltage which is not optimum. I would like to hear from others who actually have a balancer installed if the upper and lower halfs are also offset by 100mV

90days.pngHello! i have exactly the same problem. Batteries 200 Ah 48V. When charging, the voltage on all batteries is different. The difference is about 0.3V from the top battery to the bottom (ladder). Over time, the BMV-712 shows that mid point deviation is increasing. Have you solved this problem?
90days.png (105.1 KiB)