Voltmeter vs. Ampmeter - Team Camaro Tech
Electrical & Wiring Troubleshooting electrical.

 
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post #1 of 4 (permalink) Old Jul 25th, 03, 11:18 AM Thread Starter
BUD
 
Join Date: Aug 1998
Posts: 71
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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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post #2 of 4 (permalink) Old Jul 25th, 03, 11:45 AM
Senior Tech
 
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Location: Austin, TX, USA
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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

Dave
========================
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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post #3 of 4 (permalink) Old Jul 25th, 03, 12:10 PM
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Jim
 
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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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post #4 of 4 (permalink) Old Jul 25th, 03, 02:01 PM
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Mark
 
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Read these:

https://www.camaros.net/cgi-bin/forum...;f=10;t=001615

https://www.camaros.net/forum/ultimat...;f=10;t=001606

The ammeter in a camaro is a millivolt meter, not a true ammeter. It uses the #10AWG main power lead from the battery to the horn relay as a shunt to simulate a value of AMPs on your guage.

Mark Canning
1969 Indy Pace Car
350/300HP RPO Z11

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