question

jamesinwa avatar image

Interested in forum views regards bank configuration.

Actual bank comprising 20x 55ah agm.
Been coming across lot of articles. posts etc regards actual available capacity depending upon how configured.

Had intended to just go 4 in series then combine the 5 strings in parallel.

Other option thinking 10 in parallel x 2 strings series to produce 2 x 24v banks of 10 then combine those. In this setup running across a lot of differing opinion as how to configure. Two straight end to end of 5 in series or 5 x 2 in series connected parallel.

Basically all configurations make sense for differing reasons am leaning towards cross string grouping as apparently provides better charging balance across the entire bank but will hold my hands up and admit just dont know so many conflicting opinions.


AGM Battery
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2 Answers
Alexandra avatar image
Alexandra answered ·

@JamesInWa

Yes there is a rather confusing amount of information out there.

The books energy unlimited and wiring unlimited by victron are the most useful learning tools. As they are well illustrated and use simple language, shows how to wire up banks.

I personally find it easier to work it out in kwh to be honest rather than ah.

55x12x20 so you have a 13.2kwh bank (if used to flat or 100% depth of discharge - which on agm you dont want). So work on half that at most. So 6kwh useable for bank life.

Stay within the c rating of your batteries. Higher voltage banks are more efficient, less losses because of ohms law. And allow smaller cabling so cheaper and easier to install. But balancing between the strings is tricky that is why products exist for that.

In our experience when building a bank you will need a bit of maintenance including rotating batteries in it every few months (ohms law also covered in the book) and also have a decent 12v charger as well to charge up the lower or struggling batteries in the bank as well, and shorter strings are better.

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Will check out the references
seb71 avatar image
seb71 answered ·

If those were cells, maybe some other configurations would be worth considering.

But since they are batteries, make strings of 4 batteries in series (for 48V) and put those strings in parallel (using busbars on which individual battery strings are connected).


But before all this: do you already have these batteries? If not, scrap the entire plan and go for LiFePO4. These are much better suited for solar than lead-acid (any variant of lead-acid, including AGM).

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Yes already have , LifePO4 a bit down the track still.
Capacity will be 55Ah x5 = 275Ah for any arrangement (as long as it remains a 48V battery bank).