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Forum Index : Solar : Best way to string 40 deep cycles for 48 volts
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mad jack Newbie  Joined: 26/06/2020 Location: United StatesPosts: 11 |
Hello all this is my first question and I hope it is not stupid. I have just got 40 deep cycle AGM batteries and need help with setting up my bank. So question is 10 parallel strings of four in series . or 4 series strings of 10 parallel .And what will make one option better than the other . Thanks to everyone for all the help and information available here |
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| Solar Mike Guru  Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Not a stupid question at all, problem having many batteries in parallel is getting equal current distribution between all cells in the parallel group, means some sort of very thick copper bus bars are required, or connecting cables all the same length. It may be easier to go with your first option, depending on situation.. Our 48v battery bank is 24 x 6volt lead carbon 300AH cells, these are arranged in 3 sets of 8 series strings paralleled together. Reason for doing this is the batteries are mounted in steel racks bolted to the floor and wall (don't want them to fall over in an earthquake); each rack frame holds 8 batteries; it would be a very messy situation to arrange them any other way. Each 48v string has its own breaker fuse dis-connector, the 3 strings terminate in 400A copper bars, all cables to each rack frame are the same size and length to keep current distribution the same. If a battery goes faulty, you want to consider how easy it will be to remove it whilst possibly keeping the system live, series strings allow one group to be disconnected for maintenance. Cheers Mike |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Completely agree with Mike, connecting multiple batteries in parallel, particularly secondhand batteries of unknown history can create future problems. Ten parallel strings, each with four in series will enable you to check/monitor each battery individually. If one battery fails or becomes weak, you can disconnect that string and carry out whatever maintenance is required with minimum disruption to the rest of the battery. Cheers, Tony. |
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| mad jack Newbie Joined: 26/06/2020 Location: United StatesPosts: 11 |
Mike ,Tony Thanks for the help . Mike do you use two pole breakers on each string to open both pos. and neg. or some other system to fuse / disconnect the strings. Also for the buss bar I have 8x40 mm brass bar aprox. 1 meter long that I can make it from . will 2agw (33.6mm2)be large enough for each string to buss bar connection |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
https://www.ebay.com.au/itm/Circuit-Breaker-C65H-DC-2P-2-Pole-250V-DC-Solars-Energy-Air-Switch-Amps-Newest/264758360060?hash=item3da4d3f7fc:g:RUYAAOSwooxe349y Cheers, Tony. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
You can use circuit breakers for string isolators BUT: they must be non-polarized type, as currents can be bi-directional, the directional types have a +- symbol on them and must be wired accordingly for the internal magnetics to work. I use HRC fuses in a holder that also acts as switch when pulled open by lever. 1 fuse in the +ve line in each string. The common bus-bar outputs have a large non polarized 250A circuit breaker supplying system. Cheers Mike |
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disco4now Guru Joined: 18/12/2014 Location: AustraliaPosts: 896 |
A good explanation of polarize and non-polarized circuit breakers here for anyone like me who need to find out about this. Gerry Latest F4 Latest H7 |
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| mad jack Newbie Joined: 26/06/2020 Location: United StatesPosts: 11 |
Tony , yes I use 63a 400v like that before charge controllers to protect them . when I had them over paneled I saw 70+ amps through 60 amp controllers so removed some panels and added breakers ,Mike I don't find HCR fuse holders so have ordered 10 two pole non polarized breakers , With ten strings of 195 Ah I don't want to take chances . Gerry , thanks for the link good information for a beginner like me . Last thing I need is to burn down my shed  |
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