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Banana?
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Topic # 239909 10-Aug-2018 11:01
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Hi,

 


We have a small solar system at the bach to run house lights and chargers etc (12V) (we have no mains connection, nor the ability to get one).

 

We have 210 Ah of AGM batteries (2 x 105Ah), charged by 2 x 150W solar panels though an MPPT controller. This is OK.

 

I have sourced a really sharp deal on two more batteries - 155Ah Wet Cell Depp Cycle batteries (x 2).

 

I am looking at getting another two panels, and another MPPT controller, so charging this bank of batteries is fine, it is using them that I am wondering about.

 

 

 

Does anyone know of a way of parallel wiring the output of both the above banks of batteries (we need 12V output) so that they aren't 'backcharging' each other (thereby confusing their respective MPPT controllers).

 

Failing that, is there an automatic switch that would switch from one bank to the other in the event the first bank gets below (say) 50% charge and then switches back when the first bank is recharged? I know I can get manual switches (as used on boats/caravans), but if I left it manual, it would not get switched over until the battery bank was flat, thereby reducing overall battery life.


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  Reply # 2071315 10-Aug-2018 13:56
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Just use high current diodes. But get Schottky type. As they have 0.25V forward drop. Instead of the usual 0.6V drop.

Rip open an old computer power supply. They normally have a few dual 30A ones.





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  Reply # 2071320 10-Aug-2018 14:01
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For higher current loads, use double pole switches or relays. Connect up each supply to 1 pole, then link the load side contacts together. So the batteries will only be linked while a load is being drawn.







Banana?
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  Reply # 2071346 10-Aug-2018 14:09
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Thanks,

 

I barely understand what Diodes do (allow current to flow one way only?) and as far as I can tell, Shottky Diodes are for higher current/faster?

 

Are you saying if I used Diodes on both (say) positive output cables, then joined them together, with a common negative, this will allow both banks of batteries to operate in parallel, without current flowing back from one bank to the other?

 

Appreciate your help.


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  Reply # 2071379 10-Aug-2018 14:56
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In simple terms - think of diodes as 1 way valves for electricity. They do cause some voltage loss, which is why I said to use the Shottky type. As they are lower loss.

So yes, exactly as you said





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