HI,
Looking for advice here. We have a 24V AGM batteries bank built with 6x 12V/225A batteries. What is the best practice to wire them? Why?
Most of the diagram I find online show wiring of 3 parallel strings of 2 batteries in Series (3P2S).
It seems that this wiring has the disadvantage of allowing individual battery serial strings to get unbalance. I even saw the case were failure of one module in the string lead to overcharging of the other battery in the same string as the parallel branched fed the defective battery branch to maintain end terminal voltage while the battery bank was off. This failure mode is what most of the time ends-up destroying simple 12V parallel battery bank as each of the 12V module is a 6 cell series.
Alternatively the batteries can be wired as a series of 2 blocks each composed of 3 batteries in parallel:
The 2S3P wiring forces all the batteries in the same voltage group to remain balanced. Two possible options are shown. Case 1 only requires that the mid point link between the 2 blocks has the same cross section as the positive and negative leads. Case 2 series connection should normally only carry 1/3 of the current and can therefore be smaller in cross section. Similarly the link between mid point does not need to be large as theoretically, it should not carry or Carry a very little current. I would not design for less than 1/3 of the main section should one battery fail.
If one of the battery fails, it can be easily detected by measuring the mid point voltage and small error can be corrected with the Victron battery balancer. Previous system would require 3 balancers or 3 individual voltage measurements.
I do not seem to see any reference to the latter scheme in the online literature. Only 3P2S wiring type is shown. What am I missing?