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.

Jeff


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

On 03/14/2016 9:56 AM, 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.

Jeff



My expectation is yes, they do fail from age/power cycles. Most likely
failure point is the wire to passive element junction...why not take it
apart and see?

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

On 14/03/2016 16:56, 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.

Jeff



They also have a current limit , but I do believe than can fail by
deterioration or something

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.

On Monday, March 14, 2016 at 12:56:59 PM UTC-4, 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.

Jeff

They most certainly do die of old age. As do regular current-limited fuses. If ever one wants some very dry amusement, bring a glass fuse close to its current limit and watch the filament dance inside the glass.

Peter Wieck
Melrose Park, PA

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.

wrote:
On Monday, March 14, 2016 at 12:56:59 PM UTC-4, 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.

Jeff

They most certainly do die of old age. As do regular current-limited fuses. If ever one wants some very dry amusement, bring a glass fuse close to its current limit and watch the filament dance inside the glass.

Peter Wieck
Melrose Park, PA

That may be what's going on inside the 2Amp 3AG fast blow fuses I
installed in the four metal bodied table lamps I'd added "touch dimmers" to.

When the 150 watt bulbs I use in those lamps burned out the "thermal
arc" would often send the touch dimmers to the graveyard, so I added
fuse holders and fuses to the lamps. Those fuses protect the touch
dimmers, even though I have to replace a 15 cent fuse almost every time
a bulb burns out.

It's still worth having touch dimmers in the lamps because SWMBO and I
don't have to stick our arms up under the lamp shade and fumble around
for the rotary switch on the socket.

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

My opinion is electrical peak ( = overvoltage ) !


Jeff Wisnia a écrit :
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.

Jeff

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.

Ha! RS was my thermal fuse and sketchy crimp terminal supplier of choice
too.

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.

Jeff


After having the thermal fuse in our dishwasher fail several times, and then
an aftermarket part fail on the first time it was used, I bought some from
Digi-Key. Hmmmph, should have known better, DON'T solder it in without a
heat sink! The (2nd) new part seems to be working fine. Instead of $15
each for a nice piece in a plastic housing with 1/4" quick-connect
terminals, I can get a bare sensor/fuse for $1.50 from Digi-Key.

Jon

Jon Elson 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.

Jeff


After having the thermal fuse in our dishwasher fail several times, and then
an aftermarket part fail on the first time it was used, I bought some from
Digi-Key. Hmmmph, should have known better, DON'T solder it in without a
heat sink! The (2nd) new part seems to be working fine. Instead of $15
each for a nice piece in a plastic housing with 1/4" quick-connect
terminals, I can get a bare sensor/fuse for $1.50 from Digi-Key.

Jon

Yes, I definitely thought about using a heat sink when the thermal fuse
arrives and I solder it in place.

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

On Tuesday, March 15, 2016 at 12:29:33 PM UTC-4, Jeff Wisnia wrote:
Jon Elson 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.

Jeff


After having the thermal fuse in our dishwasher fail several times, and then
an aftermarket part fail on the first time it was used, I bought some from
Digi-Key. Hmmmph, should have known better, DON'T solder it in without a
heat sink! The (2nd) new part seems to be working fine. Instead of $15
each for a nice piece in a plastic housing with 1/4" quick-connect
terminals, I can get a bare sensor/fuse for $1.50 from Digi-Key.

Jon

Yes, I definitely thought about using a heat sink when the thermal fuse
arrives and I solder it in place.

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

Make sure any plug in types have a clean and tight contact, or there'll be heat generator at the plug.

"N_Cook" wrote in message
...
On 14/03/2016 16:56, 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.

Jeff



They also have a current limit , but I do believe than can fail by
deterioration or something

All fuses die eventually, but in most cases they outlive the equipment.

Once or twice I've even seen corrosion kill a fuse, but most thermal types
are in sealed encapsulation. That would be an unlikely failure mode.

wrote in message
...
On Monday, March 14, 2016 at 12:56:59 PM UTC-4, 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.

Jeff

They most certainly do die of old age. As do regular current-limited
fuses. If ever one wants some very dry amusement, bring a glass fuse close
to its current limit and watch the filament dance inside the glass.

Thermal fuses are often installed with crimp connections to avoid high
failure rates during soldering.

Occasionally, a bad crimp makes a resistive join that heats up and pushes it
past the trip point.

John-Del wrote:
On Tuesday, March 15, 2016 at 12:29:33 PM UTC-4, Jeff Wisnia wrote:
Jon Elson 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.

Jeff


After having the thermal fuse in our dishwasher fail several times, and then
an aftermarket part fail on the first time it was used, I bought some from
Digi-Key. Hmmmph, should have known better, DON'T solder it in without a
heat sink! The (2nd) new part seems to be working fine. Instead of $15
each for a nice piece in a plastic housing with 1/4" quick-connect
terminals, I can get a bare sensor/fuse for $1.50 from Digi-Key.

Jon

Yes, I definitely thought about using a heat sink when the thermal fuse
arrives and I solder it in place.

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

Make sure any plug in types have a clean and tight contact, or there'll be heat generator at the plug.

Not a plug in type. This thermal fuse just has its leads soldered to
lugs on the heater's thermostat and its heating element.

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

John-Del wrote:



Make sure any plug in types have a clean and tight contact, or there'll be
heat generator at the plug.
Yes, the kit that came with the aftermarket replacement had all this, and I
replaced it, but it still blew the thermal fuse the first time we used it.

The Digi-Key replacement has held for several months, now.

Jon

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.

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