Wednesday, May 6, 2020

Re: [electricboats] 48V system cirucuit breakers? Vs. Fuses?

John,
Can you clarify what your application is please?  You mention an electric motor that "can pull up to 100A" to be used "in a proof of concept type experiment".
Are you putting the motor aboard a vessel or testing on the bench?  [More specifically, what's the potential degree of loss in the event of a fire?  If you're running your system on a bench in a controlled environment where the loss might be a burnt wire, that's one thing.  But taking people aboard a vessel on the water requires an entirely different standard of care!] 
Do you know what motor (nominal rating in watts) the battery pack was intended to power? And what concepts are you looking to prove?
Ampacity of a wire is a function both of diameter/gauge *and* length.  In some situations, a 12 awg wire might safely carry 50 amps for brief periods, but it would not be prudent to create such a situation where there's meaningful risk of property or life.
I'm not an engineer or expert by any definition, but I would take the cautious approach, and size my load wires for the maximum expected load and required length of wire.  For 100 amps, over a few feet or so, that would mean 8 awg to me.  [I'm using 150 amp ANL type fuses and 7 awg wire to my motor that could pull 150 amps.]
Will there be any other loads on your battery?  Ideally, each load would have its own fuse, and your battery fuse sized to allow for the entire system.
Take a look at <https://newwiremarine.com/circuit-protection/> for a useful illustration [no endorsement of the vendor intended].
Good luck, and have fun!
[-tv]
Tom VanderMeulen
"Grace O'Malley"
Cape Dory 27
Monroe, MI
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