Blade-style rubber fuse holders Suck!

[Mashurst]

I guess I learn slow. It took me three tries to figure this out, so I thought I would drop it here.

When I first wired my jeep up to a Renogy 20 amp DC to DC battery charger in the bed, I had some 12g zip wire lying around, so I used it. I knew it was undersized for the job, but it worked for a bit until the rubber blade-style fuse holder under the hood of the truck melted itself and the fuse to a charred blob with an open circuit, and my charger stopped working. The fuse does not seem to have blown so much as been ripped apart by the lack of support plastic and rubber.

That is strange. Why didn’t it blow the fuse? So, I redid the wiring with 10g, which is what I should have done from the start but I again used an inline rubber fuse holder and didn’t think anything of it. After a year or so, I got the same result with a melted, charred mess.

This time, I’m going to do it right I said! I’m going to go all the way to 8g. Man, if that don’t carry the 25 amps nothing will. Again, I used a big rubber blade-style fuse holder with a 40 amp fuse.

I got 11 months of feeling like I had solved that problem once and for all until this happened.



At this point, it finally occurred to me that maybe the current was not the real problem. Maybe the under hood temperature was the issue. I still don’t feel like I fully understand what the deal is with these things, but I started looking for temperature ratings on them, and there is no such thing. I can’t find a rating from any source or manufacturer. Powerwerx, where I got the dang thing from, gave me a bunch of excuses and tried to tell me fuses should never be used in an under hood environment… Ummm, find me a car that does not have a fuse box under the hood. They never gave me a temperature rating or any reasonable answer as to why this would happen.

My solution will be to try MRBF Terminal Fuses mounted directly at the battery terminal. They are rated for up to 125c, which should work better under the hood. Maybe more importantly, they don’t have a bunch of fuel-like stuff warped around the high-resistance part of the circuit.

The more I think about the inline fuse holders like this, the more I hate the design.

 

[jonyjoe101]

I suspect the fuses might be the cheap chinese made ones. I have had those fuses melt. For high amp devices like my 30 amp tire inflator, I only use the bussman fuses, those don't melt and will pop at the rated amperage. I prefer the fuses in the hard plastic, not the see-thru plastic. I never had one of those melt.
Also the wiring has to be pure copper OFC, 10 gauge pure copper should easily carry the 25 amps without heating up. I use 12 gauge pure copper wire on my 30 amp tire inflator without any problems (it averages about 25 amps while running).
I have seen those fuse holders used inside the engine compartment area, they shouldnt melt unless they are actually touching the exhaust pipes or hot engine parts. The cheap chinese fuses I wouldnt trust on any high amp situations.
I checked the renogy manual
For 10 gauge wires they recommend 30 amp fuse, for 12 gauge wires they recommend 25 amp fuse.

 

[llamalander]

Ah, thanks Verkstad, beat me to it being simple! Well here's a bunch more words...

Connections are usually where electrical things go wrong. You may have stayed within the fuse rating but a poor connection inspired currents much hotter than the housing could handle. Resistance is electrical energy transformed into heat, and that is a self-reenforcing cycle: the hotter the conductor, the less energy passes through and the more heats it up.
A poor connection may arc as well, which is a low-amperage, high voltage spark, which is often incredibly hot--far beyond what any insulation can endure.

You are probably right that inline fuse holders are crap, especially with a few tries at it. Something as simple as a twist-tie or a zip-tie might prolong the life of a suspect piece of kit, but a well-made fuse holder will probably give you less trouble. Change that before upping your wire size or shopping for the "best" fuse.

Blue Sea prints some great charts on both wire size and fuse sizing, which are more generous than one might expect, because they account for nuisance tripping--which is more generous than how I learned--

 

[Mashurst]

Well, Powerwerx got back to me with the following:

The manufacturer states the operating temperature range of IFH-08-12 is -20 to 75C.

So 167f... I don't think one could trust the passenger compartment of a car to stay under that on a hot day. Forget about the engine compartment. So ya. As I said, these things suck, and I will never use them again for a vehicle application.