Jim,
Personally, I try to the voltage drop in my drive system to less than 1% whenever it is practical. My battery DC cables are 2/0 and my short controller to motor AC cables are 2 gauge. I figure that there are enough connections between batteries and between components (fuses, switches, contactor, shunt, etc.) that reducing the resistance in the wire as much as reasonable will help keep the overall system resistance in check. But we're all making our own choices for our own boats. I'm sure that the boat would work with just 2 gauge everywhere, but I believe that the extra size will show up as more reliability and maybe some extra efficiency in the long run.
It's the same with the rigging on the boat. I size my running and standing rigging where normal usage is in the low percentages of safe working load. That way, there is room for mistakes or normal wear and tear before something breaks.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "luv2bsailin" <luv2bsailin@...> wrote:
>
> Thanks Tom.
> I had a feeling I was missing something LOL. Looks like I'm a couple years out of date. That's the "over 50V" one right? Now I have to go find a copy of that one. Guess I should have asked my brother Scott, I'm pretty sure he's an ABYC member and has all that stuff. Too bad he's 2000 miles away or I'd go steal his copy.
> Anyhow, I was shooting from the hip as usual, now I feel like a dumb-ass, as usual.
> Those AWG sizes still seem way big to me, though my background is in aircraft wiring where they cut things a little finer due to weight concerns and also use higher-temp insulation. I'll be interested to see what TE-30 says and what is their rationale for such conservative wire sizing.
> Anyhow, another "for what it's worth"...
> I put together a little spreadsheet that shows various allowable wire lengths that would give a 3% of 48V drop at 100A. You can scale it up or down as it's just simple Ohm's law.
> awg ohm/ft len amps drop
> 6 0.0003951 37 100 1.46
> 4 0.0002485 58 100 1.44
> 2 0.0001563 92 100 1.44
> 0 0.0000983 146 100 1.44
> 00 0.0000779 185 100 1.44
> What I take away from this is that voltage drop in the wire is NOT the main driver in wire gauge selection for the lengths we typically deal with in our boats.
> I think I'll read up on what the current standards say about fuse sizing before blathering on about that in detail. Suffice it to say, the fuse needs to be sized to protect the wire from meltdown in the event of a dead short.
> I hope somebody finds this useful.
> Regards,
> Jim McMillan
>
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