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QUOTE]Originally posted by Wes V in a different thread in a different forum:
This may be a little confusing but, most of the factory "ammeter" set-ups are in reality a volt meter that reads across a know shunt resistor. The face of the meter is made to display amps.

The shunt resistor is normally mounted near the horn relay, which is also where the original regulator is.

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The thread in question is http://www.chevelles.com/forum/Forum29/HTML/002980.html

Ok, yeah, I'm now confused. I never took those electronics classes I meant to.

What does it really mean to be an voltmeter reading across a shunt resistor? I understand meters and resistors, just not the way they work together. I remember reading about places that convert factory ammeters to voltmeters, if what you've got already is a voltmeter then why would you want/need to?

Sorry if this has already been covered somewhere. I couldn't find it if it has.
 

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Derek,

The "ammeter" in your '65 is in fact a voltmeter that is wired to measure the voltage drop across a shunt (a resistor - in this case just a piece of wire). In this case, the meter reads in the positive direction when the alternator is charging and in the negative direction during discharge. The current the starter draws when you start the car does not pass through the meter. A real ammeter can have a lot of current passing through it at any given point in time (headlights, blower motor, wipers etc. all on at the same time = 30, 40 or more amps) which presents the potential for a major melt-down under your dash should something short out. It is for this very reason that GM and others use a voltmeter to measure the voltage drop across a shunt resistor (the voltage is proportional to the current passing through the shunt) to show you the effective charging (or discharging) current. Much, much safer this way! Hope this helps.

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Dave
My 65 Elky & 2002 Camaro SS
Tri Power #1,Tri Power #2
New Richmond 5-Speed
Fan/Shroud/PRC Radiator
Richmond Road Race 5-Speed, 3.07's
 

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What the conversions are doing is replacing the faceplate with one displaying volts instead of charging/discharging. They also rework the resistance to provide the proper readings at the true voltage level. The original ammeter/voltmeter works in the milli-volt range.

There is no need to change. Some just prefer a voltage reading instead of the chraging/discharging indication.

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Brian TC#1092, ACES#4374
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1965 El Camino Before Restoration
1981 Corvette
 
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