I had something wierd happen tonight

[grampi 10+ year member]

I was playing around a bit with my newly installed system adjusting the crossover points and such when all of a sudden I lost all sound from my speakers. The HU stayed on, but no sound. The first thing I thought might be wrong was the fuse in the amp's main power lead coming from the battery. I pulled out the fuse and the glass tube on the fuse between the two metal end caps was broken. I tested the fuse using a DMM and it read good continuity. I thought it was very wierd that the glass portion of the fuse was broken but it reads like a good fuse. Have any of you ever seen anything like this? I don't have another like fuse so I'll have to wait until tomorrow to pick one up to replace it with. Another strange thing is I wasn't even really cranking on the system that much. I had this very same system (using a different HU though) installed in another vehicle and I've cranked on it a lot harder than I was tonight and I never blew a fuse before. In fact, this was the original fuse that came as part of the wiring kit I purchased 5 years ago. Do fuses go bad over a period of time, or could I have a shorting problem. I don't see how I could possibly have been drawing over 60 amps of current (that's the rating of the fuse) without either there being some sort of a short, or the fuse was somehow bad. And if the fuse actually blew, why is it still showing continuity on the DMM? Shouldn't a bad fuse read as an open? And why would it break the glass? This whole thing is just wierd.

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[mdillon 10+ year member]

heat and cold through season changes could break it down over time i guess.

 

[grampi 10+ year member]

Well for one thing, I looked up the fuse rating my amp is supposed to have (Kicker KX 600.4) and it should be an 80 amp fuse. The one that was in there was a 60. I'm guessing with deterioration over time and being a lower amp rated fuse was probably the cause for it to blow.

 

[audioholic 5,000+ posts]

There is no 'deterioration over time' for fuses. I mean if you want to talk about over decades, sure. But realisitically, no.

How does a fuse work? It has a small amount of material in it, of a specific size, shape and material, that allows it to pass a certain amount of current through it for a certain amount of time before the material melts, breaking the circuit. So, what could/would change this? Molecular breakdown of thee material into another form? Oxidization? Ive seen fuses literally rusted solid to their fuse holder, and still pass current thru them just fine.

Mechanical circuit breakers degrade over time, they use parts like springs that lose their tensile strength over time/use, altering their trip point. Fuses do not have this constraint, its one of their big advantages over CB's.

To answer how the glass broke, I dunno, weird. Maybe it had a flaw from the factory (in the glass), maybe you broke it while installing it and didnt realize it, maybe a rock flew up and hit it. I dunno. But no, even passing too much current through the fuse to the point it burns in half shouldn't break the glass.

 

[grampi 10+ year member]

It was definitely the fuse that was bad. I picked up a couple new ones from Radio Shack this morning. Unfortunately they didn't have any 80 ampers, so I got another 60. Installed it and the system is back to normal. I'm still curious as to why the bad fuse showed good continuity. Anytime I've ever took a meter to a bad fuse in the past it's shown an open. This one didn't. Wierd.

 

[audioholic 5,000+ posts]

If the fuse had continuity, it would have still worked. That's the whole point of a fuse.