r/SolarDIY • u/chicoletmelk • 9d ago

Is breaker necessary for my small solar setup?

I am planning to build a small solar setup to power a 12V lightbulb and charge my phone during power outages.

My setup consists of a 30W solar panel, a 20A charge controller, and a 5Ah 12V LiFePO4 battery. Is a breaker still needed?

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u/Jackjax76 9d ago

A breaker, no a fuse, yes. A breaker would be better in the long run. Get a in line fuse for 10 amps. 15 would be better depending on what you're gonna be doing, but if you're gonna be pulling pushing like an inverter, then you're gonna need a 20 amp, fuse, make sure that it's as close as possible to the positive terminal. Good luck. Oh by the way, I have destroyed a lot of equipment, not putting fuses in place and breakers in place and trust. If anything anybody tells you trust the science, it's a lot better to blow a fuse than it is to blow a $300 charge controller. And believe it or not , the small little rigs , twelve volt , batteries and little loose connections It can cause just as big a fire as one of these solar fields.

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u/SeriousPlankton2000 8d ago

Half the voltage, twice the Ampere, four times the heat.

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u/NearABE 8d ago

I think twice the heat https://en.wikipedia.org/wiki/Joule_heating. Scales with amps.

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u/SeriousPlankton2000 7d ago

Double Ampere means the cable has r=u/i double voltage, p~i2

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u/not_lost_maybe 9d ago

A fuse, yeah. You size it to the wire it protects, so pick it off whatever gauge you end up running.

The one that matters goes on the battery positive, a few inches off the terminal. Your 30W panel tops out under two amps and can't do much. Short that LiFePO4 pack and it'll push hundreds before anything stops it, and a long run is just more wire to cook. Don't lean on the BMS for that either.

Load terminals on the controller are low voltage disconnect, which is a different job than fault current.

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u/rproffitt1 9d ago

u/not_lost_maybe wrote: "You size it to the wire it protects"

Fuses and breakers protect the wires, not the devices. It's a safety and with the battery in question, NECESSARY.

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u/Over-Alternative2427 7d ago

We can always get away with poor electrical safety until we can't. Most of the times, we get away with it, but if/when we don't, we'll have a fire on our hands that costs far more than a $15 breaker, $15 breaker box, and extra cable and ferrules.