fuses?

fauss · May 2016

When and where do you use fuses? I'll have 2x100 watt 12v panels a 40 amp mppt with 2x6v golf cart batteries. Off grid shed.

So from my understanding I would need one on the positive in between the charge controller and battery. Since my mppt is a 40 amp would I want a fuse smaller than that?30amp? And what about the load side? Still a newbie.

Mountain Don · May 2016

At the charge controller consider using Midnite MNEPV breakers. They come in many sizes and mount to a DIN rail. For convenience one on the incoming side (from PV array to charge controller) and one on the output side to batteries is good. Most controllers require connection to the batteries first and then to the PV. using breakers means an easy means of making / breaking the circuit.

Breakers / fuses are there to protect wiring from overloads. So with a 40 amp controller capcity you would size the wire for that amperage and use a 40 amp for the protection device. (MNEPV breakers are rated to full load rating unlike some.)

The breaker / fuse between charge controller and batteries should be as close as possible to the batteries. But not in the same box / enclosure as the batteries.

Do yourself a favor and also install good lightning surge protection, like the Midnite SPD.

Load wiring should also incorporate fuses / breakers.

vtmaps · May 2016

As per Mt Don, use some Midnite breakers and boxes.

Regarding the breaker between the battery and controller: with a 40 amp controller you should use a 50 amp breaker and cable capable of handling 50 amps... that would be at least #6 copper. The controller's output should not ever be able to trip the breaker.

In the event that the controller faults, it could be a direct short circuit across the battery. That is why you have the breaker.

Everything, without exception, that connects to the battery must have a fuse or circuit breaker.

--vtMaps

oil pan 4 · May 2016

For 2 100 watt panels I would use a 20 amp fuse from the panel to the charge controller, because each panel is only going to make around 5 amps. Then put a 30 to 40 amp fuse from the charge controller to the battery since the MPPT will bump up the amps going out to the batteries.
I fuse for the panels I have, not the capacity of the charge controller, but that's just me.
Yeah, use at least 6ga wire to the battery.

fauss · May 2016

Thanks for the responses. More questions. On my panels it says Max Series Fuse Rating. So do use a 15 amp fuse for each or on both after I run them in parallel? Then use a 50 amp fuse on 6 gauge wire close to the battery. (is 4 gauge better?) Also is this the fuse I want going to the battery?http://www.midnitesolar.com/productPhoto.php?product_ID=217&productCatName=Breakers&productCat_ID=16&sortOrder=20&act=p

vtmaps · May 2016

fauss said:

Thanks for the responses. More questions. On my panels it says Max Series Fuse Rating. So do use a 15 amp fuse for each or on both after I run them in parallel?

With only two panels, you do not need a circuit breaker.

fauss said:

Then use a 50 amp fuse on 6 gauge wire close to the battery. (is 4 gauge better?) Also is this the fuse I want going to the battery?http://www.midnitesolar.com/productPhoto.php?product_ID=217&productCatName=Breakers&productCat_ID=16&sortOrder=20&act=p

4 gauge is always better than 6 gauge... as long as it fits into the conduit, the terminals of the breaker, controller, etc.

The breaker you show a link for is a din rail polarized breaker. Consider one of these:
http://www.solar-electric.com/installation-parts-and-equipment/midnite/cipr1/stfubr1/pamodccibr.html

--vtMaps

fauss · May 2016

OK thanks vtmaps I'll pick up on of those. And I'll use as big of wire as my charge controller port can handle. Where do you buy your wire and connectors? Online or at a Lowe's or home depot ?

Different topic. I'll have 2 6v 208ah GC batteries. What kind of charger/tender would you suggest? Sorry for all the random question.

oil pan 4 · May 2016

Will 4ga even fit in the charge controller?

vtmaps · May 2016

oil pan 4 said:

Will 4ga even fit in the charge controller?

I guess that depends on the controller. Of course, you could use 6 gauge between the controller and the breaker, and 4 gauge between the breaker and the battery.

--vtMaps

fauss · May 2016

What about between the batteries

vtmaps · May 2016

fauss said:

What about between the batteries

As always, thicker and shorter is better. What do you have for loads? Do you have an inverter? The greater the currents (amps of charging or discharging) and the longer the wires, the thicker the wires need to be.

--vtMaps

fuses?

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