Electronics > Projects, Designs, and Technical Stuff
Under-rated fuse question
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ejeffrey:
PTC trip characteristics are much worse than metal fuses. Unless you mean to mount it to the load resistor and turn it into a thermal cutoff.  A thermal fuse or cutoff switch seems like the right solution for this application based on the information we have.
Ice-Tea:

--- Quote from: ejeffrey on March 29, 2019, 02:41:28 pm ---PTC trip characteristics are much worse than metal fuses. Unless you mean to mount it to the load resistor and turn it into a thermal cutoff.  A thermal fuse or cutoff switch seems like the right solution for this application based on the information we have.

--- End quote ---

I know PTCs suck to dimension right. But it might still be valid option in case resetability is an issue or such events are expected on a regular basis.


--- Quote from: T3sl4co1l on March 29, 2019, 03:17:57 am ---Put a Klixon(R) in series with the load.  (Or if I misremembered or misspelled that brand, it's a thermal switch.)

Tim

--- End quote ---

Airpax?
SeanB:
Klixon self resetting or manual reset unit,or thermal non resettable cut out attached to the resistor. The one time thermal fuse is easy to attach with a small slide on sleeve of silicone coated fibreglass sleeving, and will both provide insulation and good thermal coupling. you typically choose a thermal fuse of around 110C, so that it will not fail in normal use, with the resistor typically reaching 70C surface temperature in the 15 seconds of on, and with the heat soak after. Longer time on it will reach the 110C point and the thermal cutout will melt, most likely after around 5 minutes.

A fuse is not good, it will be replaced with another of different rating, or will be replaced with one not of the same brand, with different trip characteristics, or will be wrapped in foil. You can get small thermal cutouts that will provide protection that are the same size as the one time unit, but they need the non resettable unit as back up as well. Thermal fuse is both rugged, reliable ( they will melt at rated temperature, with up to 5C below it as margin, and will never fail to operate) and cheap, plus needs minimal extra protection, other than a regular fuse to protect the rest of the circuit and wiring from faults, probably here a 1A slow blow fuse.
Jester:
Thanks for the comments,  I decided to go with a thermal cutout, more expensive than a fuse, however it should be more reliable. 
Neomys Sapiens:
I would not recommend to make it a self-resetting one, as some are suggesting. If overheating happens (by your description), there was a violation of the control signal, which should be investigated/corrected!
The other possibility is to rebuild the device in such way, that it can tolerate being switched on continuously without overheating.
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