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Voltmeter or Ampmeter

Discussion in 'The Garage' started by mrk5, May 6, 2004.

  1. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    So which is better, ampmeter or voltmeter? I was thinking that an ampmeter would be better. /forums/images/graemlins/dunno.gif
     
  2. 4xcrazy

    4xcrazy 3/4 ton status

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    I would think the ampmeter would be better, i have had alternators go bad where it puts out 14volts, but the amperage was gone, nothing nadda, zip. I do not know exactly how they work, but this is what happened.
     
  3. HarryH3

    HarryH3 1 ton status Author

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    An ammeter requires that the output wire from the alternator run inside to the gauge and then back out to the battery. It forces all of the current to go through the shunt on the meter. As the current requirements increased and alternators pumped out more and more current, the manufacturers determined that a voltmeter works better. They didn't need to run a heavy gauge wire through the dash any more.

    A voltmeter will give you a very good idea of what's going on. It should be right in the 13.5-14 volt range when everything is working properly and the engine is running. If it goes higher, then the voltage regulator has failed. If it goes lower, then either the alternator or voltage regulator has failed (or the load exceeds the output capacity of the alternator!).

    If the voltage gauge works right, then there is no way that it could stay at 14 volts with a dead alternator. The voltage will immediately drop to 12.5 volts or so when the alternator stops charging. Then the voltage will continue to drop as the battery discharges.
     
  4. 4xcrazy

    4xcrazy 3/4 ton status

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    Actually thats right, now that i remember it more, and you mentioned that when they die they drop to 12.5, thats basically what id did, but when people see a 12.5 volt reading out of an alternator, on a 12 volt system, they think it is still good.

    My bad, it had been awhile and memory is starting to go with the age thing creeping up with me.
     
  5. ZooMad75

    ZooMad75 1/2 ton status Premium Member GMOTM Winner

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    This could get into a debate like which is better, Pepsi or Coke. Personally, I prefer a Voltmeter. They are easier to install (wiring wise) and I prefer not having all that Current running into the cab and back out again. Too much could be done if the circuit is shorted to ground.

    The difference is that an ampmeter needs to be installed into a circuit in series to the curcuit you want to measure the amps on. So you have to run the wiring all the way from the alternator (or where you want to pull from) and back again so that the Ampmeter is in line of the curcuit. This is carrying the entire load of the curcuit as well so if you got a 100+ amp alternator you better have some serious curcuit protection and large gauge wiring.

    Voltmeters on the other hand can be put in parallel to the cirucuit you want to monitor. The current load is small and can run a smaller gauge wire for hook up and pull right from the fuse panel or directly to the battery.

    My 75 had a ampmeter originally and I swapped it out for a voltmeter from a 78-79 truck. I could not use the factory wiring in the cluster, if I did I would have had a total meltdown. I did bend back the tabs in the cluster that the ampmeter snapped into and ran new wires off of the back of the voltmeter to a Keyed on plug in the fuse block and the other wire to ground. This way the voltmeter only is working with the key on. Hook directly to the battery and it will run all the time, killing the battery. I've got a late model 110 amp alternator on my serpentine belt setup and it runs at 14volts all day long, but it is sensitive enough to see the addtional loads drop the voltage down becuase of the higher amp draw. This is when the lights or blower moter get turned on.

    As for loosing an alternator that was still pushing 14v with little or no amperage, you could still see the effects of the lack of amp output. dim lights, slower blower fan speed or power window speed. That in addtion to the fact that the battery would probably die after a long enough time of use with no recharge.

    By no means are either gauge the best they both have positives and negatives (really bad pun) but they are there to alert the driver of an issue before its too late. You got to pay attention to rest of whats going on in the operation of the vehicle to confirm what the gauges are telling you.

    Ever have an oil pressure gauge read Zero but the engine runs fine? Still shut it off right? I have, turns out the line broke and It was pumping the oil out the broken line but as long as it still had oil it sounded fine. Its the same type of situation.
     
  6. HarryH3

    HarryH3 1 ton status Author

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    [ QUOTE ]
    As for loosing an alternator that was still pushing 14v with little or no amperage, you could still see the effects of the lack of amp output. dim lights, slower blower fan speed or power window speed.

    [/ QUOTE ]
    The gauge reading would still drop. It's the lower system voltage that would be causing the "dim lights, slower blower fan speed or power window speed". /forums/images/graemlins/wink.gif /forums/images/graemlins/cool.gif
     
  7. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    Thanks for the help. I think I will go with the voltmeter, sounds like it will do what I need and it will be easier to install. Like to stick with the old KISS principle. /forums/images/graemlins/waytogo.gif
     
  8. u2slow

    u2slow 1/2 ton status

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    An external-shunt type ammeter like this one.

    The shunt is mounted under the hood with the heavy guage wire. Then you run little weenie wire to the guage in your dash.

    I prefer BOTH voltmeter and ammeter... the more gauges the better /forums/images/graemlins/thumb.gif
     

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