Reliable Thermal Fuse 1

[Maxham1]

We're looking for a reliable thermal fuse at around 90C to be used on a printed circuit board. The problem with the fuses we've considered is that they can go off prematurely due to degradation of the fusing material.

Would any one have information on a more reliable type of thermal fuse? We'd like to keep the size of the fuse to about 1/8 inch diameter and 1/2 long. Or, surface mounted would be acceptable.

Thanks,

Dave Maxham

 

[jraef]

"degradation of the fusing material" ???

Over how long? Are you sure that the fuse is not just doing what it is supposed to do?

"Venditori de oleum-vipera non vigere excordis populi"

 

[Maxham1]

We're told that the trip point for the thermal fuse will drift down in temperature over time.

 

[Electricliff]

You don't specify the current you are passing through this fuse.
In my experience some of the smaller thermal fuses do self heat adding their own contribution to the device temperature.
Another problem with low temperature thermal fuses running at high currents is the connection method.
Often the recomendation is to crimp the connections to the terminating wires. (This is to prevent premature failure due to the soldering temperature.)
I have found thermal fuses running at 10Amp fail randomly due to poorly crimped wires. We carried out a series of tests where we monitored the millivolt drop across our crimps over a period of time. The results showed a number of our crimps exhibited a slowly rising millivolt drop with time. At some point the rate of rise accelerated and the self heating of the crimp was sufficient to promote a fuse failure.
This happened earlier and more often if the operational ambient temperature was elevated.
We overcame the problem permanently by building an efficient heat sink shunt to clamp over the fuse and its lead out wires and then soldered the connections.

Its worth checking all possible conditions that might raise the internal temperature of the fuse before you condemn the device. It may be just doing what it was designed to do!!!

 

[Skogsgurra]

"We're told that the trip point for the thermal fuse will drift down in temperature over time"

Is that what the vendor says? Or his competitor? I would ask for some references rather than "be told".

 

[Bung]

A properly specified fuse properly installed will not suffer from "trip point ... drift down in temperature over time".

Current flow through a metallic device will only affect the melting point of that device if the current is high enough to cause an adverse heating effect.

Bung
Life is non-linear...