Quote:
Originally Posted by cgmv123
Breakers/fuses protect wiring, not devices. A 5 amp fuse can and will pass current significantly in excess of 5 amps.
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Indeed. A "fast-blow" fuse will generally require twice the rated current for a period of 0.1 seconds in order to blow, a standard fuse generally requires twice the rated current for a full second before blowing, and a slow-blow fuse requires twice the rated current for a period of 10's of seconds to blow. The danger of putting a fast-blow fuse on a motor is that the motor may pull current near the stall current level for a short time while they're starting up, so a fuse innocently (and incorrectly) used to protect a motor from stall may blow as the motor is spinning up.
LEGO has a
thermal fuse that they designed to help protect a motor during robot development. It's not fool proof either, many motors have met their maker due to poor design (the fuse generally can't pop fast enough to save a motor from a sudden and absolute stall), but just as many have been saved from near-stall situations allowing the fuse to blow before doing fatal damage to the motor. The benefit of the LEGO power cable is that it's a thermal fuse, so when it cools it will close the connection back and the motor will come back to life; the problem is that you don't want that on your competition robot because once the fuse pops it may take a minute or two to come back, and the fuse's protection ability seems to degrade each time it pops.
-Danny