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Victron Balancers on 2 parallel 48 volt (4 x 12 volt series) strings)


oryx
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Good day solar buffs. I have two series strings (4 x 12 volt each) connected in parallel on a Mecer 5000 / W PF 1 system.  Victron's pamphlet regarding the connection of their battery balancers is a bit ambiguous. I have purchased 6 balancers for the two 48 volt strings. My question A: Do I need 6 balancers, as told by the tech expert where I purchased them, or only 3 balancers for the two strings in paralllel.  Question B: Exactly how are the 6 balancers connected across the 2 banks of batteries? Specifically with respect to interconnections between the balancers and the battery banks. I hope you can help me.

Battery_Balancing-730x369.png

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Hi Oryx

Welcome on the forum. You could have done the same with 3 balancers, but with the correct fusing between the banks to ensure that one parallel string can disconnect from the other string should something go wrong. 

BB.PNG.1ad838b2085661eb952189e99d952716.PNG

 

2 hours ago, oryx said:

Question B: Exactly how are the 6 balancers connected across the 2 banks of batteries? Specifically with respect to interconnections between the balancers and the battery banks. I hope you can help me.

 Please look at the drawing above, the interconnection wires can be 1mm square as only 0.7 amp will be used as a balancing current. But I will put a 5 amp fuse inline at all the inter connecting wires. Please remember to keep all wires exactly the same length to ensure there is no difference in resistance between the lines as this can effect the sensing as well as the balancing process. 

In your case , just disregard the third string.

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You can link the middle points with a fused connection and thereby get away with just 3 balancers instead of 6. If you don't want to link it, you need 6. You pretty much pair the batteries up pairwise, and then a balancer goes across the poles as in the figure.

There is a reason why the midpoints are not generally linked (but don't ask me right now what it is), but according to Victron documentation you are allowed to do it.

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Good afternoon everyone,

Jaco and Plonkster,

Thanks for the info. I have since contacted Gerrit Tromp of Victron who also confirmed that only three balancers are necessary. Three installers have to date argued with me regarding the need for balancers, stating that the interconnecting cable should just be the same length. They ignore the fact that batteries will have different internal resistance, or just don't know. I have been measuring the voltages across the batteries, before and after installation of the balancers, and am now even more convinced that they are required for longer lasting and happier batteries.

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