When I planned the wire sizes for my launch, i figured I'd pull a max of 125A, usually much less. I started with what ampacity is allowed by the ABYC standards. A 4AWG cable with 105C insulation that is not bundled with other conductors has an ampacity of 160 amps when installed outside of the engine space.
Sounds fine? Well, no.
Although the 4AWG cable will safely handle the current, I also needed to be concerned about the length of the cable run and the resulting voltage drop from the resistance of the cable. The voltage drop is wasted heating the cable, and within reason, there is no point in wasting the power we have available.
The 4AWG cables with a cable run of 20 feet (entire cable length) would have a voltage drop of over 5.1% on my nominal 48V system. That's 51W at 20A, and 318W at 120A.
By using 1AWG I have a voltage drop of about 1/2 of 1%, which wastes about 3W at cruising speed, or 25W at max possible speed. Larger cables will have less loss, but I'm happy to lose only 3W when I cruise at 500W-1000W.
-Tom
*From:* Richard Mair <fullkeel2000@...>
> > *To:* electric boats <electricboats@yahoogroups.com>
> > *Sent:* Sunday, March 13, 2011 6:53 PM
> > *Subject:* [Electric Boats] wire size
> >
> >
> > Just wondering what wire sizes people are using to set up the series
> > connections on the batteries and connect them to the motor..
> > 48 volt system with a max draw of 100 amps. Most times I expect to be
> > in the 20 amp range from the anticipated figures
>
> I'm using what I think is welding cable on my installation. The 400amp
> controller said to use 4 AWG wire. Even though I have a 100amp motor and
> usually run at 40amp, I wired with wire recommended anyway. I bought
> lengths of the wire from a AV supplier and made up the lengths my self.
> However I think my local boating shop sells premade 4guage battery
> leads. I haven't looked too closely but they look like the same wire I used.
>
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