Fuse prices and lack of sellers - Has the world gone INSANE?

[Paul Moir]

Depends on what you're doing.

[JoeN]

My old microwave (25 years old) went out last year, simply an internal fuse, had to take the cover off to find it.  9 out of 10 people these days would have pitched it.  The fuse must have aged, the microwave is still 100% good, no problems with the rest of it.  I got to learn how the triple interlock safety switches work inside it, pretty neat.  No problem finding a replacement at Walmart, just an appliance fuse, nothing special there.

[SeanB]

My old microwave (25 years old) went out last year, simply an internal fuse, had to take the cover off to find it.  9 out of 10 people these days would have pitched it.  The fuse must have aged, the microwave is still 100% good, no problems with the rest of it.  I got to learn how the triple interlock safety switches work inside it, pretty neat.  No problem finding a replacement at Walmart, just an appliance fuse, nothing special there.

Which internal fuse, the one on the mains side, generally an 8A or 10A ceramic one, or the longer high voltage fuse, that I find generally fails with old age, and which is a $5 part off the shelf, supplied complete with leads. I wonder about the HV ones, they look awfully like a regular 32mm glass fuse, just in a blast proof case.

[james_s]

I've only ever seen a fuse on the mains side in a microwave, and these are some of the only fuses that I've seen blow where replacing the fuse gets it going again.

Usually the cause is one of the door interlock switches sticking briefly. Microwave ovens have two interlock switches, one that is normally open, closing and enabling the oven when the door is latched. The other is normally closed, shorting across the primary of the power transformer and opening when the door is latched. If this one sticks, the fuse will blow.

[SeanB]

HV fuse is a long black plastic part, with 2 red leads and spade connectors on it, one straight and one right angled. Used from the transformer secondary terminal to the capacitor, and even there on the cheap ones with the nasty thin metal, the CCA transformer and the 36VAC fan and turntable motors driven with a resistive dropper on the switching PCB just above the fan, which also has the fuse and a power relay and inrush limiter there as well so they can use a thinner wire inside the unit.

Present on pretty every microwave I have opened in the last decade or so. I keep a few as spare parts to fix microwaves, often removed from ones scrapped from rust in the cavity.

[james_s]

Maybe it's something that's required in your part of the world and not mine? Doesn't sound familiar to me, normally on the secondary side there's just the capacitor, diode and magnetron.

[JoeN]

My old microwave (25 years old) went out last year, simply an internal fuse, had to take the cover off to find it.  9 out of 10 people these days would have pitched it.  The fuse must have aged, the microwave is still 100% good, no problems with the rest of it.  I got to learn how the triple interlock safety switches work inside it, pretty neat.  No problem finding a replacement at Walmart, just an appliance fuse, nothing special there.

Which internal fuse, the one on the mains side, generally an 8A or 10A ceramic one, or the longer high voltage fuse, that I find generally fails with old age, and which is a $5 part off the shelf, supplied complete with leads. I wonder about the HV ones, they look awfully like a regular 32mm glass fuse, just in a blast proof case.

It was a normal fuse, it was near where the mains entered the box, and was replaced with a Bussman 10A ceramic fuse I got from Walmart in a small pack of various sizes.  I didn't even see the other ones and I don't remember seeing it in a paper schematic that was taped up inside the microwave enclosure either (that was a weird surprise to find that).  This is a really old microwave, from about 1992, 100% mechanical, no ICs at all, no display, just a mechanical timer, and exactly one power level which seems appropriate for most anything that you should be trying to microwave.  I love it.

[JoeN]

I've only ever seen a fuse on the mains side in a microwave, and these are some of the only fuses that I've seen blow where replacing the fuse gets it going again.

Usually the cause is one of the door interlock switches sticking briefly. Microwave ovens have two interlock switches, one that is normally open, closing and enabling the oven when the door is latched. The other is normally closed, shorting across the primary of the power transformer and opening when the door is latched. If this one sticks, the fuse will blow.

That may have been it.  I remember slamming the door sort of funny when checking what I was cooking (needed more time) and the timer was on so it reengaged immediately and blew.  Mine has three switches and what you say is what I noticed in the schematic and though was clever.  Two were NO and the third is NC.  If the NC one doesn't open up (as it should) when the door is closed, it crossbars the mains and blows the fuse.

[SeanB]

I have an old (circa 1980) microwave, and eventually the timer wore out. While i could fit another in there, I rather did a simpler mod and put a mains rated pushbutton switch and a industrial timer module, so that I had a 2 minute timer instead, and a single push gives you 2 minutes of operation. Open door and it turns off and resets the timer.  I did replace the mains fuse once when it blew from the inside lamp failing. Replaced the lamp a few times, and other than that it is still the same parts as new, and as it has no turntable but a air driven stirring vane in the waveguide feed area it does not wear the cavity.

Amazing a KIC microwave still works nearly 40 years on, and is in regular use. Those switches can be a pain when the door wears, as they now use a single plastic latch mechanism that holds the switches and it can deform with time and heat.

And yes, every single microwave has a schematic of the wiring inside the cover, complete with the part numbers of the switches and fuses, and with the part numbers for all the things like magnetron, transformer, capacitor and diode. You also in some get a protection diode, basically a 3kV avalanche diode there in case the magnetron fails, to break down with the overvoltage and short out, blowing the mains fuse. A pox though on manufacturers that use a single security screw on the cover, the rest being regular pan head self tapping screws. Takes an extra minute to open the cover every time, and i generally just replace it with a regular generic microwave screw.

[TheAmmoniacal]

I am also looking for a new 440 mA fuse for my U1272A (10 × 35 mm 440 mA/1000 V fast-acting fuse, HRC, SIBA). I just can't convince myself to spend $15 for one - cheap arse, I know   

[madires]

Some local prices from a known reseller:
- ESKA 6,3x32 mm, 1000V, 0,5A, ff, 30kA HRC    EUR 1.80
- ESKA 10,3x38 mm, 1000V, 10A, ff, 30kA HRC   EUR 7.80
- SIBA 10x38mm, 1000V, 10A, ff, 30kA HRC         EUR 4.99

Both are German manufacturers.

[Nauris]

If you are not going to probe big high voltage battery packs or directly at the transformer, then normal gG 10x38mm cartridge fuse should be good enought, and they cost only like 2€ a piece.

[MrAl]

Hi,

When i look around, i see some fuses are cheap like 0.31 cents (USD)  each while specialty fuses are more expensive.

[nanofrog]

I am also looking for a new 440 mA fuse for my U1272A (10 × 35 mm 440 mA/1000 V fast-acting fuse, HRC, SIBA). I just can't convince myself to spend $15 for one - cheap arse, I know   

FWIW, the least expensive source I've found for HRC fuses in Agilent/Keysight DMM's, is to buy directly from Agilent/Keysight.  Granted I know you're not in the US, but what harm will come from checking it out?