Small off grid solar system query !
Submitted: Monday, Mar 26, 2018 at 21:52
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GREG T11
Hello all. I have a small problem that is doing my head in. I wish to setup a permanent solar system on a onsite caravan. At this point in time I wish to run a 40 ltr fridge and led strip lights for a max of 2 weeks at most ( xmas ) and intermittent use at other times.
I have got five three y/o 33 ah UPS deep cycle batteries previously used in data room duty that I bought cheap and have charged up
well and are holding charge. These are my practice batteries that I intend to run in parallel. The first of my problems starts here. trying to obtain the correct way of running the positive power off the bank. Some examples show it just feeding in one end and out the other or a more centralised
junction. Ummm. Wtf
I bought Collyn Rivers motorhome and solar book and IMHO was a waste of money. Piss poor diagrams for the few that were there.
Reply By: Allan B (Sunshine Coast) - Tuesday, Mar 27, 2018 at 01:46
Tuesday, Mar 27, 2018 at 01:46
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Hi Greg,
I assume that your batteries are 12 volt each and that you require a 12v system. In that case you will be connecting the three batteries in parallel.
All you need to do is jumper your positives together and same for the negatives, then your take-offs can be wherever convenient, at either end or in the centre, it matters not. All that is important it to use adequate sized cable so that there is no voltage difference at each battery. For your current needs I suggest no smaller than 6 sq.mm cross section (10 gauge).
You may see published advice of taking the positive from one end and the negative from the other, and even more fancy arrangements, accompanied with expressions of avoiding voltage differences at the battery terminals. But in practice, none of this is necessary if adequate cable size is used. It is an elaborate scheme with application only to very large currents but is sometimes touted to impress the reader.
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Follow Up By: RMD - Tuesday, Mar 27, 2018 at 09:26
Tuesday, Mar 27, 2018 at 09:26
Same for the whole 5 batteries too.
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Follow Up By: Allan B (Sunshine Coast) - Monday, Apr 02, 2018 at 18:58
Monday, Apr 02, 2018 at 18:58
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Yeah thanks RMD. I should have said five, not "three".
The "three" belong to their age in years. doh.
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Follow Up By: GREG T11 - Saturday, Apr 07, 2018 at 20:39
Saturday, Apr 07, 2018 at 20:39
Thanks people, it is starting to make sense.
O.K today I got a 285w panel and a Victron 100/20 controller and some other odds and ends ( have already got 4mm twin sheath tinned solar cable and some 10mm tricable for the battery connections along with a proper crimping tool ).
But... when connecting the solar controller to the bank do I follow the same theory. As in + and - charge cabling onto one battery only and load off the other end, or run the load directly from the controller.
Cheers Greg
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Follow Up By: Frank P (NSW) - Saturday, Apr 07, 2018 at 20:47
Saturday, Apr 07, 2018 at 20:47
I would run the load directly off the controller. That way the controller will supply the load and any excess output will go to charging the battery.
If the load is not present, e.g. a fridge not actually running, then all the output will go toward charging the battery.
If there is not enough sun to run the load, the regulator will automatically power the load with what is available from the sun and make up the difference from the battery.
It is usually better to charge a battery with no load on it. The above promotes that as much as possible while still guaranteeing power to the load.
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