When I said the resistance in the cables wastes energy as heat, I didn't mean that you could keep your coffee warm with them! :)
But the math works, and the energy is consumed, although it is dissipated along the entire length of the cable and inside a good thermal insulator.
I think what it really comes down to is that the builder needs to decide what percentage of the total power on board should be allowed to be lost due to the cable's resistance.
-Tom
--- In electricboats@yahoogroups.com, Dennis Wolfe <dwolfe@...> wrote:
>
> A personal data point on this wire size discussion: My first launch
> used 2ga Ancor marine wire (about 20' from front-most battery to
> controller) 48v, motor drew about 85a at WOT. I did one "how long will
> it run at WOT until the controller overheats into fail safe mode" test.
> The answer was about 25 minutes. With this extreme use the wire never
> even felt warm.
>
> Second boat is 72v max 75 amps with 4ga marine tinned wire. I haven't
> done an extended WOT test but in propeller testing the wire never even
> felt warm.
>
> Heavy gage wire is very heavy and very expensive, it makes sense to put
> in only what you need.
>
> When I was screwing around with a 12v trolling motor running at 20a I
> found noticeable warming in the cheapo 1/4" spade connectors MinnKota
> used. RC bullet connectors ran much cooler.
>
> I would bet that in many of our do-it-yourself systems the quality and
> workmanship of making connections is more significant than the losses in
> the wire itself. It is important to correctly size the lug to the wire
> and use a crimping tool properly sized to the lug. Adhesive lined
> shrink wrap sealing the lug to the wire insulation is good practice too.
>
> Denny Wolfe
> www.wolfEboats.com
>
>
>
>
> On 3/14/2011 1:31 PM, Lonner wrote:
> >
> > While you are considering wire size and insulation, don't ignore the
> > type of wire itself.
> >
> > One person posted having used welding cable for battery connections,
> > etc. I have removed and replaced several boat's primary battery wiring
> > that were welding cable. These systems were failing because welding
> > cable is made with non tinned wire and the insulation (jacket) is
> > usually of a type that doesn't necessarily prevent water intrusion if
> > submersed. Typically, I found green slime corrosion, wicking away from
> > the terminals as much as a foot!
> >
> > If you operate in salt water, look for fully tinned marine grade wire
> > and cable. If I remember correctly, that spec. is also included in the
> > ABYC recommendations.
> >
> > Sailonner
> >
> > _,_._,___
>
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