Do thermal fuses fail from old age?

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Over the years I've had a few thermal fuses in houshold appliances go open for no apparent reason. When I've replaced them with ones with the same temperature rating they stayed working fine for years more.
A couple of days ago our three year old Bunn coffee maker quit, because a 141 degree celcius overtemperature thermal fuse on the water tank opened. It might possibly have happened because the water tank thermostat stuck closed, but after I repaired it the thermostat cycled just as it should.
I was suprised to find that there were TWO identical thermal fuses connected in series located right next to each other, the bodies were actually touching. That seemed like a belt and suspenders approach, unless there's a significant likelihood that a thermal fuse won't open when it should?
Comments?
Thanks guys,
Jeff
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Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
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jeff_wisnia wrote:

I understand they work on bi-metal strips. They can fail from fatigue. Won't reset when temperature goes down cooling off.
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"Tony Hwang"

** Nope - that is a temperature switch.
Thermal fuses like this one use the melting point of some material and rely on a spring to open the circuit.
http://media.digikey.com/photos/Cantherm%20Photos/SDJ1%20DF100S.jpg
.... Phil
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But I assume the same applies. The metal heats up and expands somewhat when in use and contracts when not. That will eventually cause it to fail.
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"Larry Fishel" "Phil Allison" :

But I assume the same applies. The metal heats up and expands somewhat when in use and contracts when not. That will eventually cause it to fail
** Maybe so - but has nothing do with bloody bi-metal strips.
.... Phil
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This is the type Peavey have hidden in the mains transformer of the Classic 30. I only discovered it by accident when I decided to dissect an "open circuit" one, no mention in the schematics AFAIK.
The owner had had 2 mains transformers replaced previously, seems, from Googling, these transformers are woefully underpowered and often break. Wonder if the only failing part is actually this switch?
Gareth.
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"Gareth Magennis"

** Eeee - yep.

** We must be leading parallel lives ..........
I actually have a power tranny from a PV Classic 30 in my used parts bin.
The thermal fuse was open - it resembled the one in my pic.
I replaced it with a new one of slightly higher temp rating and it works fine.
The customer got a new tranny, as requested.
... Phil
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Phil Allison wrote:

I fiddle with guitar amps. Son is into playing guitar/bass and drum. Have a crude set up for recording as well. Have some vintage Marshall, Fender, Boogie amp. Guytron and Soldano. Hugh & Kettner. Built couple Fender clone and Marshall JMP clone from mono tube amp. Let kids blind test it placing it side-by-side with real thing. They couldn't tell the difference.
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On Thu, 22 Mar 2012 00:03:41 -0400, jeff_wisnia

I wouldn't think they fail just from age, but what do I know?
I r eally posted to ask how you crimp them in place, what kind of connector do you use?
And where do you buy them?

May it be our biggest problem.

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I repair machines that use use them for a living, they are cheap protection. they definetely nuisance trip for no reason. oh well it keeps me working:)
they are so commonly used because of being so cheap. but it would be far better if a resettable kind were used. lots of perfectly good stuff must be tossed every year because a thermal fuse fatigued failed.
I service roll laminating machines for a living. sael, GBC, Laminex, USI, Idex, Ledco. Sadly nother manufacturer Banner just went out of business after 38 years.
the economy is far worse than were being led to believe...............: (
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When I find myself needing insullated crimp. I take one of these,
http://i00.i.aliimg.com/photo/v0/228959260/non_insulated_ring_terminal.jpg
and cut the big loop off with diags, and use the small crimp ring for my application.
Christopher A. Young Learn more about Jesus www.lds.org .
The one I replaced is about the size of a 1/2 watt carbon resistor and looks like this:
http://parts.digikey.com/1/parts/726774-thermal-fuse-141c-10a-axial-sdf-df141s.html
The way the original was installed The fuse's leads were left about an inch long and the flexible insulated wires connecting to them were fastened with little uninsulated metal crimps. I didn't have any of those crimps so I just clamped a heat sink to the fuse's lead wire and quickly soldered the flexible wire to the fuse lead with an 1/8 inch long lap joint.
(Probably more than you needed to know, eh?)
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
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Home made crimps easy enough to make.
http://i00.i.aliimg.com/photo/v0/228959260/non_insulated_ring_terminal.jpg
Cut the big ring off with diags.
Christopher A. Young Learn more about Jesus www.lds.org .

No, not more. Exactly what I need to know.
I had thought about solder but feared it would melt the fuse, and I have only one batch of about 6, each one a different temperature.
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On 3/21/2012 11:03 PM, jeff_wisnia wrote:

I could understand parallel fuses because one may not handle the current. Perhaps in series it's safer because the unit will shut off if one fails to open? o_O
TDD
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The Daring Dufas wrote:

Nasty cheap Chinese thermal fuses->higher rate of failure to open in a real overtemp condition->using two in series may keep your house from burning down, if they don't both fail the same way.
Cheers
Phil Hobbs
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Principal Consultant
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Perhaps the voltage rating was lower than the required use, ie in fused state not rated for the service voltage across the broken section so someone thought, I know , we'll put 2 in series ;-)
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so you have no visual sense for emoticons
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On 3/23/2012 5:44 AM, N_Cook wrote:

It's known as H.I.S.I., pronounced "hissy", it describes the disease Humor Irony Sarcasm Impairment. People with that particular mental disease are said to have H.I.S.I. fits and often put on a big display of pseudo-intellectualism about the subject at hand when they fail to see the humor or bizarreness of statements made by someone who is attempting to pull their leg. It's also called The Mr. Data response in some circles. ^_^
P.S. They often get mad when someone like me is teasing them. o_O
TDD
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The only theoretical justification I can come up with for having 2 same type and batch thermal fuses in series is this possibility. Over time they were getting returns where the then single fuse had blown but no one could work out whether its due to heat or current carrying. Assuming they have space to mount 2 in at production and one is closer to the monitored source of heat than the other. Then if practically all the returns showed the hotter one to have failed then its not so likely the cuurrent carrying self-heating that is the issue.
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On 3/23/2012 7:43 AM, N_Cook wrote:

I do believe I wrote something like that early in the thread. ^_^
TDD
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On Fri, 23 Mar 2012 07:04:16 -0500 The Daring Dufas

Speaking of emoticons, those look like emoticons used by the late Matthew Moulton, AKA DiaperBoy. Hmmm...
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