Question on solar controller hook up?
I finished up most of my solar install today and I noticed an issue when hooking up the solar controller to the batteries. I'm using an A/B Both switch to control what bank or banks I want to run....
Forum Discussion
2oldnslow wrote:jrnymn7 wrote:
My understanding is the fuse is to protect the controller from a shorted battery, not the other way round. Am I mistaken? ...
You are mistaken. The fuse is there to prevent a fire if a failure causes excess current to flow and overheat that wire. In this case, the most likely failure would be a short in the wire or in the charge controller. That would blow the fuse and stop the current flow.
A "shorted battery" would have no voltage and therefore provide no current to the wire or controller. The charge controller has a limited output current so it can't provide enough current to overheat the wire, even into a short.
It doesn't matter which end or the middle of that wire has the "issue"
It is current that blows the fuse. The rule is to have a fuse rated to blow before the wire is melted. The wire has a gauge and length that sets its "ampacity" and the fuse on that "branch" wire should allow that many amps on that wire and not much more, or the wire will become the fuse and if in a wall it will cause a fire where it cannot be seen until too late.
You have several current sources or demanders (inverters eg) each on its own "branch" which has its own wire gauge and fuse to match that current.
They all go to a "bus" and that bus has a fatter wire and a bigger amp fuse that goes to the battery. That one wire from bus to battery must be able to carry all the current from/to all the branches to the bus, so it has to be a fat gauge and a big fuse.
The 18" from the battery rule for automobiles is so in a head-on crash the battery can't cause the wiring to the boom-jang music amplifier in the trunk to catch fire beside the gas tank. (Or some such scenario :) )
That just leaves the 18" of wire by the battery to melt but it is still in plain sight and not behind a wall.
I am aware that Randy at bestconverters says that a current limited converter with a fat enough wire does not need a fuse by the battery, because the converter can't do any more amps. I am extremely uncomfortable with that advice, but don't have the expertise to refute it. So I just go with the way my trailer came, which is to have a fuse on the converter-battery line near the battery.
