Reliable Thermal Fuse

[Maxham1]

We're looking for a high reliability thermal fuse at about 90 C for use on a printed-circuit board. The problem we seem to be having with the fuses that we're considering is that they can go off prematurely due to degradation of the fuse mechanism (melting or sublimation of fuse elements)

Would any one have information on a more reliable thermal fuse? Ideally the fuse would be the same size as our currently-used fuse (1/8 diameter, 1/2 long approximate). A surface-mount thermal fuse would also be acceptable.

Thanks,

Dave Maxham

 

[unclesyd]

The telephone companies used to use a very rugged thermal fuse that depended on the melting of an encapsulated organic material when melted allowed the circuit to break. I had one or two and will look around and see if they can be found. Someone might remember them being used on the microwave systems.
They also had one with a fusible wire that actually broke and changed to another circuit. This device was used on the amplifiers.
.
Have you talked to Belmont Metals. They were always a great help with us in dealing with low temp metals.

http://www.belmontmetals.com/products/low-melting.cfm

 

[Maxham1]

Unclesyd,

Thanks for the input. The thermal fuse that we're currently using is exactly as you describe; it's an organic material which when it melts at a defined temperature, opens the circuit. The problem that we seem to be having is that the defined melting temperature can drift downwards as the fuse ages in any temperature environment that is close to the melting temperature. In fact, the manufacturers of these fuse describe a holding temperature, which is the maximum temperature that the fuse can tolerate for 168 hrs without opening. Our application requires a component with a much higher reliability. The manufacturers of these fuses also indicate the their fuses should not be used in nuclear or military applications. Although we don't have nuclear or military here, we do have similar reliability requirements. So I'm interested in finding something more reliable - something that's on the same size as the Elcut or Panasonic fuse we've considered (1/16" diameter or so, about 1/2 inch long. We've also looked at the alloy-based versions, which melt instead of sublimating like the organic ones, but we still can't get a good handle on their reliability.

Any help is greatly appreciated. Thanks again Unclesyd!

Dave Maxham