Ignorant question about putting a 30A Fuse from controller to batteries

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BigSkyTrailerGuy

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I just pulled the pin of a couple of 100W Solar panels and a Renogy Wanderer controller. 

They specify a 30A fuse between the controller and the batteries --  But if that cable is 4 AWG (for minimum voltage loss),
doesn't the resistance of an in-line fuse negate our coveted current flow?

Sorry again for the ignorance.
 
No the fuse is a very short section of small wire. The 4AWG is 100's times longer

The resistance is "per foot" so being as the fuse is like 1" there's not much resistance there.
 
At 200 watts you will get 12 amps or less. If you push close to 30 amps through the fuse you may see insignificant heating of it. I have experienced it with anl fuses. Gadgets like https://www.amazon.com/dp/B01H3DKGFK?th=1 are a cheap way to protect and give you an easy way to disconnect. The high quality version is this https://www.amazon.com/dp/B004XXOVP0/ref=twister_B01ENZVS7G?_encoding=UTF8&psc=1. You may also want a disconnect between the panels and the controller  because some companies specify disconnecting the panels before disconnecting the battery. Your controller manual may mention it.
 
As QZ & John say, your max current flow is nowhere near 30A, so the fuse is insignificant in the circuit resistance. 4 AWG cable is probably way overkill anyway. Even 10 gauge will handle 200 watts (about 12A @ 16v) with insignificant loss, and 10 gauge is rated for 30A loads.
 
How far from the batteries is the solar controller?  Put it close by and the need for overly large wire becomes insignificant.

In any case, you do want a fuse close to the batteries in case you get an internal short in the controller or an external short in the wiring.  Better a fuse gets hot and blows than the wiring gets hot and starts a fire.
 
Here's my 30 amp fuse setup. Being an old guy, I used the jumbo size fuse. (easier to see)  :D :D
 

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