Date:         Tue, 9 Dec 2008 19:15:05 -0500
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Voltage Drop, 4 feet extra, 4 gauge wire
Comments: To: M'obeechi <obeechi@RUNBOX.COM>
In-Reply-To:  <E1LABaS-0004vI-0J@fenris.runbox.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

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"

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