Carl Pattinson wrote:
>
> Most contact breakers are effectively slow blow fuses due to the way that
> they work.
>
> Anything other than a contact breaker would be a liability as the main fuse
> in an aircraft electrical system (ie if there were a surge you would loose
> all your electrics and changing fuses in flight is not an option - asuming
> you have a spare !)
All valid observations, but to toss in a technicality. Even a typical
fast-acting fuse can take 200% of rated current for .5 second. So,
talkin' the fuse that feeds the bus, say 25A, there's nothing in the
plane that should be able to cause 50A of surge, I would think. The
only eligible items are the sum of all avionics. The little 50-100uf
filter caps that's typically in the front end of these things just
won't do that.
The only thing I can think of that will kill the fuse on the
alternator output is dumping into a defective battery. Setting aside
whether we want to fly with that battery, there's where the circuit
breaker looks preferable. A 30A P&B W31 breaker will take 60 amps for
10+ seconds. Presuming the Rotax alternator can supply that at a much
lower voltage, it will allow time to bring up the voltage on (and
reduce the current to) a badly discharged battery (jump-started). A
30A slow-blo could pop much quicker.
Best,
Fred F.
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