Sunsaver MPPT Battery Fuse and wiring size question

whackamole
whackamole Registered Users Posts: 18
Finally got around to getting my sunsaver mppt... I have a fusing/wiring question...

The sunsaver mppt manual says there should be a 25A fuse no more than 6 inches from from the battery's positive terminal.

But the manual does not indicate what size wire to use. OK, but it does say to use a 25A fuse between the controller and battery. Based on my understanding that the fuse between the controller and battery is meant to protect the wiring, they are therefore assuming that I'll be using a wiring size that can handle over 25A? It just says to look in the wiring charts in the back to select a wiring size. But that chart lists the lengths of wire suitable for a max 3% voltage drop for a given AWG size. (Which to me is a different issue than choosing wiring based on a given recommended fuse size.)

And given that this is a 15A controller * 1.25, shouldn't the fuse here be ~20A?

I am confused as to why Morningstar would dictate a specific fuse size.

Can anyone shed light on my confusion? I figure Morningstar knows more about this than I do, but until I understand it, I'm not hooking it up....

Comments

  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    Re: Sunsaver MPPT Battery Fuse and wiring size question

    #10 wire is rated at 30 amps., #12 is rated for 20 amps.

    But with 12 volt circuits you are usually more concerned with voltage drop, since either of those would fit well within the max amperage capability of the SS-MPPT.

    The thing about the battery to controller fuse is that it is intended solely as a disaster safety device, which would occur only in catastrophic failure of the controller being shorted. Why they recommended a 25 amp instead of a 20 amp I really don't know, perhaps just to avoid nuisance blows.