# Parallel 12 volt battery charging

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I have read several articles concerning the negatives of long strings of parallel 12 volt battery's. The main concern seems to be that not all battery's will receive an equal charge when cabled lug to lug.

I have several buss bars that were used in a high current/amp AC power substation (very high Silver content Aluminum) and had the thought of running cables from the positive side of each battery to one and the negative side of each battery to another. These buss bars are 3/4" thick x 4" w x 18" long.

I would also tie my charge controller leads and inverter leads into them.

Any thought on this idea?

Thanks

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Re: Parallel 12 volt battery charging

Welcome to the forum.

For multiple batteries (or strings of) in parallel using bus bars is the preferred method. The positive and negative cables (as well as any inter-battery connections) need to be equal on each. The idea is to keep the resistance through each parallel path as even as possible. But even then there are limits because the batteries themselves will inevitably have different resistances. Over time the slight variations compound the problem. It is more noticeable on 12 Volt systems than on 48 Volt because of the relationship between Voltage and resistance.

On the whole, when you get more than four parallel batteries you're almost assured of trouble.

Also see these Smart Gauge diagrams (method #3 is what you're looking at doing):
http://www.smartgauge.co.uk/batt_con.html
Re: Parallel 12 volt battery charging

We refer people to the Smartgauge website where they have a short article about wiring up batteries so that they have balanced wiring.

Personally, I try to dissuade people from large parallel strings of batteries for lots of reasons (1 string ideal, 2-3 can work OK, over 3 and you are looking at a lot of issues). There are people with 4 or more parallel strings that are very happy with their battery banks and have good life--But they do require more work/cost of hardware/monitoring to keep the battery bank running well.

Let me ask the question a different way--Why do you want more than one to three strings of parallel batteries? Size of batteries (moving around by hand), remote location where there are not a lot of choices in what batteries to buy? Have a critical power system where you want redundant battery strings? Or simply costs--"Cheap" golf cart type batteries are hard to ignore.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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Re: Parallel 12 volt battery charging