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Bad fuse holders.

I was finishing up a project earlier today, and on hitting the power switch it's completely dead. It's operated off the line with a transformer, and after a little debugging I realize something is wrong with the fuse, or more specifically, the fuse holder. It's one of the little cup style deals like the one in the bottom right in this image:

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Inside the cup are a spring and a (brass?) terminal clamped around the wire end. I find that one half of the holder has continuity, but the other doesn't. I take that half out of the circuit and measure it with a multimeter; it reads in the megohms. At first I thought there might be some oxidation on the contact that's preventing a good connection, but nope, there's good continuity between any two points on the contact.

Cut to the chase: the stranded fuse holder wire had vaporized just inside the wire casing at the contact connection point. Evidently whatever machine was used to crimp the connectors on the ends pulled the wire too hard in the process, so at that point the wire was down to just a couple strands. Then the inrush current killed it.

I bought the fuse holders from an "overseas" supplier on eBay because I thought "They're fuse holders, what could go wrong."

Reply to
Bitrex
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And now you know why they were possibly being sold on E-Bay at such a good price. Most likely too many defects in a run and some one that works there, E-bayed them instead of allowing them to hit the land fill.

Just a prognosis of mine :)

Jamie

Reply to
Jamie

Fuse holders are a safety device and you don't care about quality or safety?

I remember using a Swiss made finger release fuse holders in the 80s with all the VDE, UL marks. It was ment to be safe to change fuses with power applied. When I got a shock and complained the answer was oh yes the data sheet is wrong!

Fuse holders can melt, have inadequate safety clearances, be marked as UL and VDE and never tested.

Reply to
Raveninghorde

Raveninghorde brought next idea :

Likely the wiring was wrong and the fuse holder was OK. Saw many of those over the years. The hot was wired to the outer end and could touched. The were Engineering Changes in the armed forces and in IBM to correct these factory faults that were nothing to do with the holder itself. :-@

Reply to
John G

This type of fuse holder is literally two pieces of wire - I thought that there weren't too many ways to get two pieces of wire wrong! As often the case, reality destroyed my assumptions, and lesson learned.

Speaking of safety, apparently some DIYers resort to constructing their own "fuse holders" out of random junk:

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Reply to
Bitrex

It's too bad, all the other items I've bought from this seller (tranistors, ics) to use in hobbyist projects have seemed to be "real deal"; at least they look and function indistinguishably from the real parts. Maybe they're all high quality fakes, I don't know - but for just projects for myself the money I save is worth the risk. I guess their electromechanical selection is not quite up to par, apparently.

Reply to
Bitrex

They are, no doubt, middlemen, and what you get today is not necessarily what you get tomorrow, even if it has an identical part number and looks very similar. It could come from an entirely different factory, be made with different tooling and materials, and have a different (or no) QC procedure. Caveat emptor.

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

I can see doing something like this in a pinch and for temporary use. Otherwise whats the point to it. By the time you buy the springs and heat shrink tubing, you could have bought a fuse holder. Plus you cant change the fuse on this thing, you have to redo the whole thing. From experience, I find heat shrink tubing to be some pretty pricy stuff.

Reply to
jw

heats shrink pricy? unless you get something fancy its a 1-2$ for 4 feet at digikey

A fuse is mostly there to prevent something from catching fire if something goes horribly wrong, not really something you should need to change

-Lasse

Reply to
langwadt

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