Polythermal fuse

[owenhooker]

Can anyone recomend a polythermal fuse to use with a 3amp voltage regulator ciruit? I'm a little confused because of the hold amperage and the trip amperage is so far apart on most. Should i choose a fuse that holds at 3amps so i can draw the max out of the voltage? regulator or should I choose a fuse that has a trip point of 3amps?

Thanks,
owen

[Chris Smith]

Stick with and experiment with standard type fuses.

Slow blow and fast,.... above and below your range.

Only your experiment will deal the correct answers out.

Also use an ammeter or chart graph to see whats going on.

Guessing over the web will only get you dangerous answers.

Also try Non reset and Reset types of circuit breakers and if your in the low voltage range [12v] at 3 amps, try some turn signal flashers in line as many of them are in this range, 2 to 5 amp, and they reset as well as they dont burn out.

Only you can watch the results. Start shy and work your way up.

[philba]

I wouldn't pick the fuse rating for the regulator max but for your expected power supply max. This may seem like splitting hairs but component max values are a bad thing to engineer to if you want reliability.

fuses are much more complex than you would think. Little fuse has a very nice tutorial (white paper? idrc...).

Personally, I'd pick a lower value slow-blow since that will safely ignore transients but pop when there is a true over current situation.

[Gorgon]

Can anyone recomend a polythermal fuse to use with a 3amp voltage regulator ciruit? I'm a little confused because of the hold amperage and the trip amperage is so far apart on most. Should i choose a fuse that holds at 3amps so i can draw the max out of the voltage? regulator or should I choose a fuse that has a trip point of 3amps?

Thanks,
owen

The trip current should be your max current. This is the max current you can have through the fuse for normal use. If your current goes above this the fuse will trip after a given time, depending on the ambient temperature and the current. To make the fuse trip 'instantly' you must raise the current to about twice the trip current. This is approx. the same as for a normal fuse.

The hold current is both the current you get when the fuse is tripped, and the current necessary to keep the fuse tripped. If you want to reset the fuse, you must reduce the current below the hold current, and then the fuse will cool and reset itself.

TOK