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.

Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.