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  • Ammeter vs Voltmeter

    I'm comfortable with the differences between what an ammeter shows and what a voltmeter shows and interpreting the readings, but what would be involved in upgrading from an ammeter to a voltmeter? I found a reference that says there's a big difference in the way each meter samples current to make its reading. Can I unplug my ammeter and replace it with a voltmeter with no other modifications and have it work?
    Corey

    Current
    87 GW "Big Bear"
    76 J20 project "Ox"
    90 GW parts rig "Velma"
    77 J10 parts rig "NoMo" (as in "no more Jeeps, Corey!")
    94 YJ "Coop"

    Past
    88 GW "Hercules" (had to sell in '08, curious who has it now)
    83 Wag parts rig "Shaggy" (used to build Herc, then scrapped)
    73 J4000 (had to sell due to PCS in '07)
    75 Cherokee "Jerry Lee" (sold in '13 because I'm an idiot)
    74 Cherokee "Dino" (used to build Jerry Lee, then scrapped)

  • #2
    Originally posted by aerocorey
    I'm comfortable with the differences between what an ammeter shows and what a voltmeter shows and interpreting the readings, but what would be involved in upgrading from an ammeter to a voltmeter? I found a reference that says there's a big difference in the way each meter samples current to make its reading. Can I unplug my ammeter and replace it with a voltmeter with no other modifications and have it work?
    No you can't just replace it. You would have to splice the wires that went to the ammeter together to keep the charging circuit in tact. The voltmeter can be installed anywhere in the vehicle that there is a hot wire and a good body ground.

    There are tons of articles on this... I am sure you have read a few. Not sure how many made it through the BB upgrade. I think there are some articles in the tech archives under "electrical" too.

    Too bad JYG can't chime in on this one...
    Last edited by BRUTUS; 12-27-2006, 10:39 AM.
    "Brutus" '74 J10 360/T18/D20/Front D60 Pro Rock & ARB/2" shave, ARB, 15 bolt FF Rear/ 4.56 Gears/38.5 x 16 TSL
    Current Jeep Status:Under The Knife
    Current Homepage Status: RUNNING

    Comment


    • #3
      I'm not sure that a voltmeter can be put in place of an ammeter because of the way the reading has to be taken. to get a good amperage reading the ammeter has be placed in series with the signal being measured (In between 2 components). A voltmeter can get a reading in parallel (externally from the circuit), I'm not sure if a voltmeter can get a reading in series. With this being said you may have to do some rewiring to get the voltmeter to work properly.

      I plan on eventually installing a voltmeter in the distant future so I'll be in the same boat at some point in time.

      Comment


      • #4
        Sounds simple enough. I'm looking for a voltmeter that will sit in the same place as the stock ammeter and look similar. I had a parts rig with one a few months back, wish I'd have kept the cluster.
        Corey

        Current
        87 GW "Big Bear"
        76 J20 project "Ox"
        90 GW parts rig "Velma"
        77 J10 parts rig "NoMo" (as in "no more Jeeps, Corey!")
        94 YJ "Coop"

        Past
        88 GW "Hercules" (had to sell in '08, curious who has it now)
        83 Wag parts rig "Shaggy" (used to build Herc, then scrapped)
        73 J4000 (had to sell due to PCS in '07)
        75 Cherokee "Jerry Lee" (sold in '13 because I'm an idiot)
        74 Cherokee "Dino" (used to build Jerry Lee, then scrapped)

        Comment


        • #5
          Originally posted by aerocorey
          Sounds simple enough. I'm looking for a voltmeter that will sit in the same place as the stock ammeter and look similar. I had a parts rig with one a few months back, wish I'd have kept the cluster.
          here you go:

          http://www.ifsja.org/forums/vb/showthread.php?p=418438
          "Brutus" '74 J10 360/T18/D20/Front D60 Pro Rock & ARB/2" shave, ARB, 15 bolt FF Rear/ 4.56 Gears/38.5 x 16 TSL
          Current Jeep Status:Under The Knife
          Current Homepage Status: RUNNING

          Comment


          • #6
            Man, I looked for a thread like that and couldn't find it. I need to get better at searching for stuff. Thanks, Brutus.
            Corey

            Current
            87 GW "Big Bear"
            76 J20 project "Ox"
            90 GW parts rig "Velma"
            77 J10 parts rig "NoMo" (as in "no more Jeeps, Corey!")
            94 YJ "Coop"

            Past
            88 GW "Hercules" (had to sell in '08, curious who has it now)
            83 Wag parts rig "Shaggy" (used to build Herc, then scrapped)
            73 J4000 (had to sell due to PCS in '07)
            75 Cherokee "Jerry Lee" (sold in '13 because I'm an idiot)
            74 Cherokee "Dino" (used to build Jerry Lee, then scrapped)

            Comment


            • #7
              You can't just unplug your ammeter. All the current going from the battery to the rest of the electrical system, except for the starter, flows through the ammeter. You have to bypass the ammeter. I didn't see what year model you have, but the quick and dirty way is to look at the back of your instrument cluster. The ammeter has two wires going to it, one on each post. Just connect both wires to the same post, and your ammeter is bypassed. It's a good idea to do that, especially if you put a higher output alternator in your Jeep. The ammeter gauge has been known to cause dashboard fires. That's not good.

              That being said, you don't have to do anything with the ammeter to also have a voltmeter. You can have both. All you have to do to install a voltmeter is to connect the negative side of the voltmeter to a good ground, and the positive side to a 12 volt side. Use a 12 volt accesory (ACCY) so as to read voltage with the ignition key in RUN or ACCY. Do not connect it to a BATT source, you could drain your battery that way.
              But switching from an ammeter to a voltmeter isn't an upgrade, it's just a different way of monitoring the electrical system, measuring different values. The ammeter monitors the total amount of current, in amps, the electrical system is drawing from the alternator and battery, while a voltmeter is measuring the amount of electrical force, in volts, the alternator and battery are outputting to the electrical system.

              A lot of the group favors bypassing the stock ammeter, because some of us tend to install larger output alternators the have far more output than the 60 or so amps the stock gauge can handle, mine is a Delco CS130 rated for 105. That makes the stock ammeter a fire hazard. So we use voltmeters to indicate the output of our alternators, since installing a voltmeter is a lot easier than going out and replacing our 60 amp ammeters with 200 amp ammeters. But you can install a much higher rated ammeter, that's not impossible, it's just not worth the cost and the hassle involved in finding an industrial grade ammeter and adapting it to automotive use.
              GP
              Last edited by Great Pharoah; 12-27-2006, 11:07 AM.
              American Jobs should be for Americans.
              Some Cheros run at 75, and some do 69,
              But if I can get mine to start and run at all, I think I'm doing fine.

              Big Mike
              "Whoopi" 80 Cherokee Golden Hawk. 360/727/208
              Horseshoe Bay, Texas

              Comment


              • #8
                I prefer a voltmeter over an ammeter any day. If the voltmeter is connected from the ignition bus (ign) to ground then one can monitor how much the battery "squats" under cranking load. Might not be a bad idea to install a 3A 1000PIV diode across the meter terminals--banded end of diode connected to the + terminal and the other end of the diode to the - terminal. This will shunt any kickback from the starter and protect the meter.

                Comment


                • #9
                  Originally posted by drlocke
                  I prefer a voltmeter over an ammeter any day. If the voltmeter is connected from the ignition bus (ign) to ground then one can monitor how much the battery "squats" under cranking load. Might not be a bad idea to install a 3A 1000PIV diode across the meter terminals--banded end of diode connected to the + terminal and the other end of the diode to the - terminal. This will shunt any kickback from the starter and protect the meter.
                  That is the problem with having JUST the voltmeter, you can only use it at startup and it tells you what you already should know, that you have a voltage drop. The battery could be dead and it will still show 12V.

                  The ammeter tells you much more than a voltmeter ever could because it is a live diagnostic of your charging system.

                  It would be like having an "oil volume guage" instead of "oil pressure guage". It is accurate DATA... but how pertinant is it?
                  "Brutus" '74 J10 360/T18/D20/Front D60 Pro Rock & ARB/2" shave, ARB, 15 bolt FF Rear/ 4.56 Gears/38.5 x 16 TSL
                  Current Jeep Status:Under The Knife
                  Current Homepage Status: RUNNING

                  Comment


                  • #10
                    Originally posted by BRUTUS
                    That is the problem with having JUST the voltmeter, you can only use it at startup and it tells you what you already should know, that you have a voltage drop. The battery could be dead and it will still show 12V.

                    The ammeter tells you much more than a voltmeter ever could because it is a live diagnostic of your charging system.

                    It would be like having an "oil volume guage" instead of "oil pressure guage". It is accurate DATA... but how pertinant is it?
                    A "dead" battery can read 12 volts--until you put a load on it. If the battery is a little tired it's "Thevenin" or internal resistance is apt to increase, manifesting itself as an even greater "stoop" in voltage during cranking under controlled conditions. A "dead" battery reading 12 volts will read close to zero when the starter is engaged.

                    The voltmeter shows how the charging system is operating by dint of the fact that the voltage reading will be higher than 12 volts--on the order of IIRC 13.5-14.5 volts or so. Much higher or lower than that range would indicate problems with the system--undercharging or overcharging.

                    While oil flow rate granted as you say is not perhaps as useful an information as oil pressure, the ammeter is a good analogy to the oil flow meter, as it measures the flow of electrons. The voltmeter is more analogous to the oil pressure gauge, as "voltage" in volts is the measure of the electromotive force--or "pressure" to push electrons at a certain rate through a resistive circuit.
                    Last edited by drlocke; 12-27-2006, 12:15 PM.

                    Comment


                    • #11
                      Originally posted by drlocke
                      A "dead" battery can read 12 volts--until you put a load on it. If the battery is a little tired it's "Thevenin" or internal resistance is apt to increase, manifesting itself as an even greater "stoop" in voltage during cranking under controlled conditions. A "dead" battery reading 12 volts will read close to zero when the starter is engaged.

                      The voltmeter shows how the charging system is operating by dint of the fact that the voltage reading will be higher than 12 volts--on the order of IIRC 13.5-14.5 volts or so. Much higher or lower than that range would indicate problems with the system--undercharging or overcharging.

                      While oil flow rate granted as you say is not perhaps as useful an information as oil pressure, the ammeter is a good analogy to the oil flow meter, as it measures the flow of electrons. The voltmeter is more analogous to the oil pressure gauge, as "voltage" in volts is the measure of the electromotive force--or "pressure" to push electrons at a certain rate through a resistive circuit.
                      Good Analogy Dr, Locke,

                      Relating "Amps to Flow" and "Volts to Pressure" Makes it easier to understand. Like it was said above in the discussion on bypassing vs. removing the ameter...you want to do a bypass in order to maintain your flow of electrons.
                      My 2 cents.
                      Later.....
                      Eric

                      ___________
                      Eric Terjesen
                      '78 Wag
                      '03 Silverado 2500 Tow rig

                      Comment


                      • #12
                        I agree with you but what I was getting at is that under normal operating conditions, the engine runs off the alternator by itself. The battery is only used for the radio, CB, lights, fans, etc (once it is started and running)

                        Ironically enough, that is how I came up with the analogy in the first place...
                        "Brutus" '74 J10 360/T18/D20/Front D60 Pro Rock & ARB/2" shave, ARB, 15 bolt FF Rear/ 4.56 Gears/38.5 x 16 TSL
                        Current Jeep Status:Under The Knife
                        Current Homepage Status: RUNNING

                        Comment


                        • #13
                          Originally posted by BRUTUS
                          I agree with you but what I was getting at is that under normal operating conditions, the engine runs off the alternator by itself. The battery is only used for the radio, CB, lights, fans, etc (once it is started and running)
                          Not exactly. The alternator powers everything while the engine is running. The battery powers everything while the engine is not running.
                          -87 Grand, 6.5L diesel, MHI TE06H turbo, Water/air intercooler, Art Carr 700R4, CS-130, hydroboost. 21/24mpg, dead 229 [Custom 242 on the way]
                          -99 XJ Limited.
                          -Jeepspeed 1717 -Built 4.0, FAST EFI, Rubicon Express, Bilstein, Rigid Industries, 4 Wheel Parts, G2 Axle, Currie Enterprises
                          -Member, FSJ Prissy Restoration Association

                          Comment


                          • #14
                            Originally posted by BRUTUS
                            That is the problem with having JUST the voltmeter, you can only use it at startup and it tells you what you already should know, that you have a voltage drop. The battery could be dead and it will still show 12V.

                            The ammeter tells you much more than a voltmeter ever could because it is a live diagnostic of your charging system.

                            It would be like having an "oil volume guage" instead of "oil pressure guage". It is accurate DATA... but how pertinant is it?
                            That's a good point. Maybe I'm just used to the voltmeter and need to think about what the ammeter is telling me and how it's useful. It might be that the best scenario would be to have an ammeter and a voltmeter, but without some explanation the average consumer (like myself until today) wouldn't find it useful. Perhaps I'll be leaving the ammeter in place after all.
                            Corey

                            Current
                            87 GW "Big Bear"
                            76 J20 project "Ox"
                            90 GW parts rig "Velma"
                            77 J10 parts rig "NoMo" (as in "no more Jeeps, Corey!")
                            94 YJ "Coop"

                            Past
                            88 GW "Hercules" (had to sell in '08, curious who has it now)
                            83 Wag parts rig "Shaggy" (used to build Herc, then scrapped)
                            73 J4000 (had to sell due to PCS in '07)
                            75 Cherokee "Jerry Lee" (sold in '13 because I'm an idiot)
                            74 Cherokee "Dino" (used to build Jerry Lee, then scrapped)

                            Comment


                            • #15
                              Originally posted by aerocorey
                              That's a good point. Maybe I'm just used to the voltmeter and need to think about what the ammeter is telling me and how it's useful. It might be that the best scenario would be to have an ammeter and a voltmeter, but without some explanation the average consumer (like myself until today) wouldn't find it useful. Perhaps I'll be leaving the ammeter in place after all.
                              NO, bypass the stock ammeter, it can cause you lots of problems if you install high current draw accessories or a higher output alternator, including a dash board fire. Anything that can draw more than 60 amps can burn you up (think big stereos, subwoofers, amplifiers, and large lights here). If you have a high output stereo, night time with headlights on, A/C on, and all the goodies you can draw more than 60 amps. Safer to do without it and use a voltmeter.
                              GP
                              American Jobs should be for Americans.
                              Some Cheros run at 75, and some do 69,
                              But if I can get mine to start and run at all, I think I'm doing fine.

                              Big Mike
                              "Whoopi" 80 Cherokee Golden Hawk. 360/727/208
                              Horseshoe Bay, Texas

                              Comment

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