Date:         Tue, 9 Dec 2008 21:45:21 -0800
Reply-To:     M'obeechi <obeechi@RUNBOX.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         M'obeechi <obeechi@RUNBOX.COM>
Subject:      Re: Voltage Drop, 4 feet extra, 4 gauge wire
Comments: To: dbeierl@attglobal.net
In-Reply-To:  <493f0a11.0508d00a.39cc.1297@mx.google.com>
Content-Type: text/plain; charset="iso-8859-15"

Gee, now I'm thinking of running the wire along the drive side mid area, then across to the passenger side (behind the front seats) to a battery selector ( ala http://bluesea.com/viewresource/69 ) then to the starting battery now on the passenger side. Thats in the ball park of ten feet, and at this point, I'm sure my wire is actually longer than stock was. I have a Subaru Legacy motor, so whatever the amps in it are... and I live in Southern California where there can be those hot days. So its sounding like 2 guage wires, I assume (naively) that running two 4 gauge is the same as running one 2 gauge. Only thing is, those battery selectors are meant for 4 gauge. 

From: David Beierl <dbeierl@attglobal.net>
To: M'obeechi <obeechi@RUNBOX.COM>
Subject: Re: Voltage Drop, 4 feet extra, 4 gauge wire

> At 06:01 PM 12/9/2008, M'obeechi wrote:
> >starting battery. Since this is DC, is that going to make a terrible 
> >difference? Will I need to use heavier gauge wire? I suppose I could 
> >wire in two 4 gauge wires between the engine and the starting battery.
> 
> Ten feet of #4 at 100 amps will drop a quarter-volt and dissipate 25 
> watts (85 BTU/hr).   Change any of the values and the rest change 
> proportionately, e.g. if your starter in the dead of winter draws 400 
> amps, you'll drop a whole volt across ten feet of #4 and dissipate 
> 100 watts of heat in the wire.
> 
> According to Bosch, you shouldn't drop more than half a volt in the 
> starter supply cable *with the starter shorted* (that's what they 
> say, but I wonder if they really mean locked-rotor rather than a 
> direct short...)
> 
>   According to DIN standards, #4 could carry 100 amps continuous at 
> 30C/80F, but you would need #2 to carry 100 amps at 50C/120F.
> 
> http://www.stealth316.com/2-wire-resistance.htm has a calculator that 
> lets you specify length and current to calculate voltage drop for 
> various AWG or DIN gauges.
> 
> 
> -- 
> David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
> '84 Westy "Dutiful Passage," '85 GL "Poor Relation" 
> 
> 

----- End Original Message -----

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