Fuse size?

My decision was I dont want controller (or the wire) to see what the battery might supply/carry untill it melts if an issue? What the scenerio might be to allow that I havent a clue. Fuses are cheap and easly replaced.

Ours 135 watt~7.6 amp panle, 30amp controller, 10ga wire. Used 15amp fuses on both positive and negative legs. 5 amp fuses on the 18ga sensor wires. 10 amp on the 16ga positive lead for load output. Fuses are cheap, needed or not I use on both sides. Electrically try to build in some over kill, but fuses I always go opposite (underkill?) less I need to see full potential of components. IE auxillary 10ga charge line is fused at 30amp. But from controller to battery, I dont know why fused beyond its output? Restriction/resistance?

I think the key word here is MAX fuse size for wire , which is 15 amp for 14 ga , 20 amp for 12 , 30 for 10 , 40 for 8 , 50 for 6 ...
But in small pv system the amps are coming to the battery , if they are coming from the battery if you have a short or a bat melt down a smaller than wire max fuse will protect the wire too , and protect the controller,
There are two numbers on a pv panel , working current and short circuit current For a fuse before the controller you go 25% more than the short circuit number , but is not needed in small pv systems less than 3 panels
The controller should be rated at 25% more than the combined working current of the panels
The flow of amps to the battery might be less in amps than the wire size max rated amps in a system because of line voltage drop
I size the fuse next to the battery to allow the amps to pass to the bat but go as low as I can to protect the pv system for bat problems or short at battery
Every system is diffrent , but if you have a long run to the bat and are using # 8 wire for line volt drop and have a pv panel that puts out 5 amps I personaly would not use a 40 amp fuse, it will work

pianotuna wrote:
Hi,

Fusing is for wire size. Fusing to protect a charge controller is pretty senseless as they are supposed to be oversize by 125%.

Not if you inadvertently use a wire that is larger than is needed which is what a lot of people seem to do,in that case you better find out what the device on the other end of the wire can handle.

oops

EVERY wire hooked to the positive post of the battery needs a fuse in it. It doesn't matter what the other end is hooked too. A short will cause hundreds of amps to flow from the battery which causes fires.

Even at 200 watts your controller won't put out more than about 18 amps.

Hi,

Fusing is for wire size. Fusing to protect a charge controller is pretty senseless as they are supposed to be oversize by 125%.

Morningstar calls for 125% of controller output rating.
They refer to NEC compliance as the reason.
Wire must also carry the fuse rating.

The wire is larger in a PV "SOLAR" system because of line voltage drop, the further the distance the more drop
A 100 watt PV panel is probably a 17 volt panel , watts divided by volts is amps , 100 divided by 17 = 5.9 amps , that can surge a small % higher than that in extreme condition
In this
chart , third one down , you can see why you have to use larger wire
With one 100 watt panel and a 10 amp charge controller Id use a 10 amp fuse within one foot of the battery , a larger one would work but wouldnt trip until 30 amps was exceeded

Hey DJ.

From what I saw of your new system, a 30A will work fine, even if you add another panel. While you are at it, you should also have one on your battery to inverter side too, depending on the size of your cable, as well as your inverter.

b

The wire you describe has a dual power source. Normally you fuse at each power source to protect the wire not the device. Fuses to protect the device if it has any would be located on the device itself.

Most charge controllers are located close to the batteries with just a short run of wire so most people just install one fuse. I placed a 40A fuse where the #6 wire from the controller (max 30A output) joins the parallel 1/0 wires to the batteries.

#12 with 20A fuse or #10 with 30A fuse would be fine.