VOLTMETER vs AMMETER

Discussion in 'Electrical Systems' started by ttopbandit, Feb 20, 2006.

  1. ttopbandit

    ttopbandit Veteran Member Lifetime Gold Member

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    Apr 20, 2005
    TX
    I was offered a free set of guages, only problem is that the guages have a ammeter instead of a voltmeter. Now, I know what kinda volts a healthy alt puts out, but how should I read this AMMETER? I've always had a voltmeter, so this is new to me. What should be the normal reading? I have a one wire set-up, if that matters at all.:confused:
     
  2. Gary S

    Gary S Administrator Lifetime Gold Member

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    Apr 14, 1999
    Bismarck, North Dakota
    Factory GM ammeters are useless. As long as everything is working right, you probably will never see it fluctuate more than a needles-width either way. You need an almost dead battery to make the needle move, and you don't ever want to get to that point.
    If possible, get a voltmeter to replace the ammeter before you instlall it.
     
  3. ttopbandit

    ttopbandit Veteran Member Lifetime Gold Member

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    Apr 20, 2005
    TX
    It is a brand new autoguage set.
     
  4. Mayhem74

    Mayhem74 Veteran Member

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    Sep 22, 2002
    tucson, AZ, USA
    Generally the go from -40 to +40. You want it to be in the middle. - Means the alternator is going out, and youre running off the battery. When you start it or if you have a really big stereo youll make the needle go into the positive, which means the alternator is charging the battery.
     
  5. Gary S

    Gary S Administrator Lifetime Gold Member

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    Apr 14, 1999
    Bismarck, North Dakota
    The aftermarket ammeter gauges read better because they are true ammeter gauges. That leads to a brand new set of problems. True ammeters have to be wired in series with the alternator charge line, so that means you have to splice into the large (usually #10) wire from the alternator to the battery and extend it with more #10 or #8 heavy wire all the way from the alternator to the interior of the car to one side of the ammeter, and from there back to the battery. Your charging current has to pass through this entire long distance circuit, and if you happen to short that wire in the future, expect lots of fire and smoke. This is why GM used a fake ammeter that really is a differential voltmeter that measures minute voltage drops between two points on the charge circuit. With the factory one, the charging current doesn't flow through the GM ammeters.
    If possible, try to find a voltmeter, or simply forget about wiring up the ammeter. A voltmeter can simply be connected to the +12 at the fuse panel and ground. They are much simpler and work better.
     
  6. ttopbandit

    ttopbandit Veteran Member Lifetime Gold Member

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    Apr 20, 2005
    TX
  7. undee72z

    undee72z Veteran Member

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    Jan 30, 2006
    Illinois
    If anything besides the starter is wired to the battery, the ampmeter will show the batterys charge rate plus the draw from any accessories wired to it.
    Has to be wired in series with the battery charge wire, if wired in series with the alternator output wire it will show all alternator output, which can be much more than the ampmeter can handle.
    Best advice here, a voltmeter also gives more info on what the charging system is doing. Which is better for monitoring a vehicle's electrical system - a Voltmeter or an Ammeter?
     
  8. jforb

    jforb Veteran Member

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    Feb 10, 2006
    sunny southeast AZ
    I kind of like the idiot light, especially with the 73-up internal regulator alternators, which work for years and years without any trouble. And it's not likely that you'll find a weak battery with a voltmeter any sooner than you would without one.

    I never even look at the voltmeters in our late model cars.
     

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