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Can a voltmeter be swaped for an ampmeter, or do you have to change the wiring. Presently have a one wire alternator and the ampmeter doesn't seem to function.
 

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In a general sense, an amp meter must have a shunt accross it's leads. A shunt is basically a small value resistor. All resistors develop a voltage drop accross them as current flows. The shut provides a very small voltage drop - just enough to swing the needle. A volt meter on the other hand has internal resistors configured in such a way as to move the needle when 10s of volts are applied. Typically a meter movement takes about 100 millivolts to swing full scale.

Now having said all that, I can't tell you exactly how an ampmeter on a car works. I believe it gets it's signal from the alternator (or generator). There must be some sort of current divider circuit in there that measures the amount of charging current and sends a current signal to the ampmeter. I'd have to see a schematic for an automotive electrical system with an ampmeter in it to give a definate answer.

While the acutal guts of the meter might be the same, the face markings and internal resitor networks are completely different.

-dnult
 

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You have to change the wiring. For one thing, most ammeters are wired in series with a main circuit to display the current moving and almost never switched so it always would remain on. A voltmeter on the other hand is usually on a switched circuit so it doesn't constantly draw current. You also need a ground wire on a voltmeter.
 

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