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Old 04-14-2021, 01:38 AM   #1
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Sizing breakers, fuses, buss bars and wire for soloar?

I'm slowly getting my solar system designed. Is there any good web pages around to help size breakers, fuses, buss bars and wire?

So far the only thing I think I have figured out is the breaker size to go between the MPPT and battery.

60 Amp MPPT and 280Ah 12 volt LiFePo4 battery. Does a 80amp breaker sound correct?

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Old 04-14-2021, 03:02 AM   #2
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The breaker is to protect the wire which needs to be sized based on your max anticipated output. What is your max output of your solar panels? You could use an 80 amp breaker but you'd need to use #3 wire and it's probably not necessary
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Old 04-14-2021, 04:55 AM   #3
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A thought to add about the idea of putting a circuit breaker between the charge controller and the batteries:
If you open the current path from the charge controller and the batteries and it is sunny out, you may fry the charge controller. The directions I have seen for my charge controllers is to connect the solar panels last to prevent damage to them. Modern inverters have fuses or breakers to prevent overload damage. Any DC circuits need to be protected through fuses or circuit breakers. I am going to use aircraft circuit breakers for my DC circuits. Breakers can be reset after tripping and if they trip a second time it is a clear sign that something in that circuit is drawing more current than the breaker is rated for.


If you attempt to pull too much current from a solar array you will get only the maximum rating of the panels in the array. Your big concern is output from your battery bank. RV battery chargers sometimes also serve as a power distribution source and are loaded with fuses. For each circuit I will have I add up the current flow for all devices on the circuit plus a margin (not a big one) and size the breaker for that. Example: A lighting circuit has one LED light that draws 800 ma (.8 amps), use a 1 amp breaker for that circuit. If the light experiences failure enough to release the magic smoke It will probably draw several amps at 12VDC, and will trip the breaker quickly. The LED light will probably not survive, but if your wiring is say 14 - 16 gauge it certainly will. This is much better than replacing a wire that goes through your wall or ceiling. Most breakers show visual indication of being tripped, so it easy to figure which one went.



One more point about wire:


If you do have over current occur in a wire with plastic insulation it may melt the insulation on that wire any others adjacent to it, possibly requiring replacement of multiple wires.
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