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From: jacobson@fluke.UUCP (David Jacobson)
Newsgroups: net.auto.tech
Subject: Re: conversion of 6 volt to 12 volt system
Message-ID: <1010@vax2.fluke.UUCP>
Date: Wed, 13-Nov-85 14:06:45 EST
Article-I.D.: vax2.1010
Posted: Wed Nov 13 14:06:45 1985
Date-Received: Fri, 15-Nov-85 04:33:07 EST
References: <362@cbuxc.UUCP>
Distribution: net
Organization: John Fluke Mfg. Co., Inc., Everett, WA
Lines: 74

> I have a 63 Ford model 4000 tractor. This is a full size agricultural
> tractor. It has a standard starting system and ignition system, the
 ...
> The problem: The 6v starter system is crummy, it turns slowly and in the
> winter will sometimes not start. I have jumped it with a 12volt battery
> and found that the started (as expected) turns faster and the overall
> starting interval is shorter.
...
> Since the generator is shot and the battery is 3+ years old, I am
> considering converting to a 12 volt system. I would replace the
> generator and the regulator with a DELCO alternator (I would use
> one with a built in regulator), the ignition coil, lights,
> solinoid, etc with the 12volt counterparts.  However, there is NO
> 12volt starter available - I must use the 6 volt starter. So the
> questions are:

> 
> 		1) can I use a straight 12 volts on this critter without
> 		   a premature meltdown (what would the voltage drop be,
> 		   etc.)
> 
> 		2) should I try to rig a voltage eater in series with the
> 		   starter and battery:
> 			a) do they make a .048ohm/750watt resistor?
> 
> 			b) is the an electronic way to do the same thing?
> 			   (e.g. SCR etc.)
> 
> 
> 		3) since the system is positive ground, can the case polarity
> 		   of the DELCO alternator be reversed or can the starter
> 		   be operated reverse polarity (since it is a D.C. motor
> 		   I would expect it to run the other way?)
> 
> 		j.r. miller, at&t bell labs, columbus, oh, us of a

Disclaimer:  I'm an electrical person more than an auto person.  I've
never even touched a tractor.

First of all, trying to float the case of an alternator is a real
loser.  Try to switch to negative ground.  The lighting system is
not going to care.  I've heard that the spark plugs might, but you are
replacing the coil anyway.

As for getting a resistor, that is easy:  just use a piece of wire. 
Looking at the wire table in an old edition of the Handbook of Chemistry
and Physics, I see that 12 gauge wire requires 629.6 feet/ohm.  So
for .048 ohms, that's 30.22 feet.  The only question is can 30 feet of
copper wire dissipate 750 watts for maybe a half a minute of hard winter
cranking.  That's 24 watts per foot or 2 watts per inch.  I'm inclined to
think it can.  Just use those 30 feet of wire in place of an ordinary
battery cable.  Coil it up somewhere in a rather loose coil to let the
air cicurlate around the wire easily.

The starter won't run backwards, as long as its not built with permanent 
magnets.  (Never heard of such.)

Even so, I'm apprehensive about the scheme, since the 6v starter
will use twice the current as a 12 volt one.  (How will a 12v
battery designed for the current requirements of 12v starters
survive on a padded 6v starter?)  Also motors aren't simple
resistors, they depend on back EMF to control the current.
(That's why a motor draws so much current with the rotor locked.)
If the 120 amps your calculations indicate is the running current,
with the series resistor it won't have as much low speed current
as it would running on a 6v battery.  Maybe that's no problem.
Maybe its even a feature :-).  I guess you could try my idea and
see if there are any ill effects.  An alternative is to talk to
people at motor rewinding shops.  Maybe someone would rewind your
starter with more turns of finer wire.  Twice the turns would
provide twice the back EMF and everything would be fine.

  -- David Jacobson    ... ihnp4!uw-beaver!fluke!jacobson
John Fluke Mfg. Co., Inc., is not responsible for any of this.