On 3/19/2016 3:14 PM, Bob F wrote:
Jeff Wisnia wrote:
Cydrome Leader wrote:
Jeff Wisnia wrote:
Over the years I've had to replace maybe a half dozen thermal fuses
which appear to have failed without ever being heated beyond their
rated temperatures.

Most recently a small electric space heater used in our office
under my desk stopped working because its thermal fuse had opened.
The fuse was a MICROTEMP G4A0 121 degree C unit, and I'm pretty
sure that nothing had blocked air passage through the heater and
caused its internal temperature to rise enough to open the thermal
fuss.

They seem to have poor aging characteristics. I've seen dead thermal
fuses in completely unused spares heater assemblies sitting on
shelves for years. Everything was x-rayed so new ones could be
custom made. Told them to leave out the thermal fuses on the new
ones.
Thanks folks, I think my guess about aging effects was probably
correct.
The only PIA for me is now that I'm retired and no longer working for
a company which does business with component suppliers I have to find
out where to buy things like those thermal fuses myself. (When Mozart
was my age he'd been dead for 45 years.)

Radio Shack used to carry thermal fuses and I could have one sent to a
local store two blocks away from our home for pickup by me at no extra
charge, but they're kaput now so I had to go online and buy one for 75
cents and pay a minimum $5.50 for S&H.

Oh well, I would have used up that many dollars in driving costs
running around trying to find one locally, and it's still cheaper
than buying a new heater.

Yes I could have just shorted it out and been extra careful using the
heater, but my luck is so bad that if someone gave me a cemetery
people would stop dying. I might burn down the whole building with
that heater and have some smart investigator tie it to my replacing
the thermal fuse with a piece of wire.

I bought a bunch from Newegg for cheap.

I bought a bunch also, I now have use for one. If only I can remember
where I put them.


I have a circuit that I built a few years ago, 12V 500ma wallwart,
driving a 7809 regulator. Recently the circuit quit working, I measured
the voltage to the 9v regulator. I was 0.328 volts, I didn't figure it
was a shorted load, because the wallwart was not warm. It turns out the
primary of the wallwart is open, most likely the thermal fuse.
It was a little odd to get the 0.328V while connected to the load, but I
guess the 7809 draws very little current at low voltage. I installed
another wallwart and all is fine.
Mikek