poll about ammeter reading

Electrical & Ignition

Your engine is running and you get 0 reading on ammeter. What do you think ?

Poll closed Saturday at 7:53 AM.
  1. Alternator is working

    83.9%
  2. Alternator is not working

    16.1%
  1. Nacho-RT74

    Nacho-RT74 Well-Known Member

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    I'm bored so I thought on a poll LOL. I would like to read what you think and votes
     
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    • alfaitalia

      alfaitalia Well-Known Member

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      Could be either....its a guess without putting a gauge across the battery terminal and seeing if you have a good charging voltage.
       
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      • Durandal25

        Durandal25 FBBO Gold Member FBBO Gold Member

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        I voted first!
         
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        • moes

          moes Well-Known Member

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          I found this article on ammeters years ago on the web.

          One of the quickest ways to get a quick health check on your electrical system is watch your ammeter! It will tell you all kinds of valuable information if you know how to read it! Most modern cars now use a voltmeter to provide limited information about your electrical system. Or even worse just a warning light to let you know your alternator has failed. Because voltmeters are now the norm the skill of interpreting the information the ammeter provides is becoming a lost art. Let’s walk through a driving sequence to understand what the ammeter will reveal about your electrical system.

          Entering the car your the ammeter should be reading "0", straight up. You may see a quick defection to the minus side if your have an interior light that comes on with opening the door. It's at "0" because you are not using any or generating any current (engine is not running). When you turn on the ignition you will see the needle move slightly to the minus (discharge) side indicating a discharge of a couple amps. This means your ignition system is getting power. When you hit the starter the ammeter will deflect sharply to the left (minus 20-30 amps) as the starter spins. The energy for the starter is being drawn straight from the battery. As the engine fires the ammeter will quickly move to the plus side (charging) of the gauge in the 20-30 amp range. The energy that was drawn down from the battery while starting is quickly being replaced by charging current from the generator. As you start driving the voltage regulator will manage the amount of charge needed to go back into the battery. After around five minutes of driving typically the battery will start to approaches full charge and you will see a reduction of charge rate down to 1-3 amps on the plus side. At this point the battery has fully recovered from the starter discharge and now the generator is putting out only enough current to maintain the charge. The voltage regulator manages the on-going charge rate.



          While your driving night time is coming and it is getting cooler. You turn on your headlights and start up the heater fan. Immediately you see the needle momentarily jump to the minus side, then come back to 1-3 amps on the charge side as the regulator manages the generator output to meet the increased demand. As you come to a stop sign and the engine speed drops, the ammeter will move sharply to the minus side, often 15-20 amps down. You notice the lights dim and the heater motor may slow. Right now your generator is not creating enough power to offset the increased load of the headlight and heater motor and is drawing backup power from the battery. This lack of sufficient power generation can fully discharge a battery if allowed to go for a long period. The short stop at the stoplight however, is not harmful. In fact, you can always bump the manual throttle to bring the idle up enough to stop the discharge. As soon as you accelerate from the stop the generator will again start generating sufficient current to replenish the energy pulled from the battery (expect a jump to 5-10 amps charge for a short period) before settling back to a trickle charge of a couple amps while driving.

          So how can you use if for some basic troubleshooting? When you first get in and step on the break pedal, the ammeter should deflect slightly to discharge as the brake lamp lights. This lets you know the battery has some charge. No deflection? Battery is probably dead or disconnected. Also when you turn on the key if you don't see a slight discharge indication your ignition is probably not connected or functional. If when turning on the key and immediate your have a full discharge (minus 35 amps) you have a dead short that needs to be repaired. Immediately turn off the key and begin trouble shooting to find the electrical short. Otherwise you risk the very real danger of a wiring fire. Might start your troubleshooting at the headlight switch as they have historically been trouble spots due to corrosion resistance in the connectors. If you are running and suddenly see a continuous discharge usually this indicates a voltage regulator issue. Try tapping the regulator case with a screwdriver handle to see if a relay is sticking and it starts charging again. On the other hand if you see a continuous rate of high charge (> 20 amps) that never goes down you may have a battery starting to fail (it's not taking or holding a charge) or a voltage regulator failing. Either way it's time to troubleshoot the generator and regulator charging circuit.

          By watching the action of your ammeter your can easily tell if your electrical system is functioning correctly. It will tell you if you have a short, your battery is full charged, how fast it is charging and how much current your are consuming while driving. Compared to a voltmeter which simply gives system voltage, ammeters allow you active monitor your electrical system.
           
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          • JimCoronette

            JimCoronette Well-Known Member

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            Based on the info provided, it could be either.
             
          • 33 IMP

            33 IMP FBBO Gold Member FBBO Gold Member

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            If the engine is running, and not discharging, the alternator is working, and your battery is charged.
             
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            • Nacho-RT74

              Nacho-RT74 Well-Known Member

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              ooooh, trust me that's all the info you need and the ammeter purpuose ;)
               
            • Glenwood

              Glenwood FBBO Gold Member FBBO Gold Member

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              Replace that thing with a voltmeter and call it a day! lol
               
            • Jerry Hall

              Jerry Hall FBBO Gold Member FBBO Gold Member

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              No, volt meter? Pull the negative battery cable off while engine is running, if the engine doesn't quit it's charging.
               
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              • alfaitalia

                alfaitalia Well-Known Member

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                ....yep but don't try that on anything mordernish….my dad found that out the hard way!!
                 
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                • srw-409

                  srw-409 Active Member

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                  My wire harness was fused when I bought the car and it was 0 all the time, so I voted accordingly. :(

                  I’ve installed a new harness but still have some things to finish up to see how it’s working. Fingers crossed.
                   
                • RJRENTON

                  RJRENTON FBBO Gold Member FBBO Gold Member

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                  I would really like to tell you but I'm sure you would not understand. To that end, how about a lesson in Ohm's Law and the fundamental operation of a vehicle's distribution system and how to read and interpret an electrical schematic diagram.
                  BOB RENTON
                   
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                  • khryslerkid

                    khryslerkid FBBO Gold Member FBBO Gold Member

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                    We need more specifics :)

                    Your engine is running and you get 0 reading on ammeter. What do you think ?

                    Engine is running and battery is fully charged with nothing turned on that would pull a moderate or heavy pull on the system.

                    No battery to complete the circuit.

                    Bad amp meter.

                    (Just my opinion of course.)
                     
                  • Nacho-RT74

                    Nacho-RT74 Well-Known Member

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                    If you are a regular driver, you see just the ammeter at 0 while driving. The rest of conclusions are on you based on that info. No more info needed that what the ammeter is showing you.

                    Everything under normal conditions.
                     
                    Last edited: Jul 29, 2020 at 5:32 PM
                  • myk r sanchez

                    myk r sanchez FBBO Gold Member FBBO Gold Member

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                    I've never seen a functioning ammeter so I really don't know...
                     
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                    • 383man

                      383man Well-Known Member

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                      I would think one of two things depending on the year of the car. First someone has bypassed the ammeter because even if not charging the ammeter should be showing a discharge. You say 0 reading as if the ammeter is not moving at all in any direction. But the car runs so if the ammeter was open it would not start and run if wired as a normal 60's Mopar muscle car. Course it could also be a mid 70's car with a shunt type ammeter which will run and show 0 reading with the ammeter itself having an open circuit. Course I am figuring its charging since you said the car is running so it had to have enough battery to start and if not charging the battery would have gone dead eventually and it would not have started. If that's whats your figuring ? Ron
                       
                      Last edited: Jul 30, 2020 at 1:57 AM
                    • Nacho-RT74

                      Nacho-RT74 Well-Known Member

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                      LOL... some you are overthinking this.

                      Car in good conditions, everything working as must be and we get 0 ( or centered needle ) reading on ammeter while driving around. Don' think something is damaged or not working propperly. You are driving and looking the ammeter ammeter is centered. what do you think ? alt is or is not working ?

                      Remote/shunt ammeter will read exactly the same than a full load ammeter. They just work with diff signal levels.
                       
                    • Nacho-RT74

                      Nacho-RT74 Well-Known Member

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                      Actually if you disconect the batt, you don't have anything to charge ( except if you get some cell phone at the cigar lighter provision LOL ). And this gives a clue about what kind of reading you get from the ammeter along with what kind of gauge is :)
                       
                      Last edited: Jul 30, 2020 at 6:08 AM
                    • HEMI-ITIS

                      HEMI-ITIS STREETER on LI FBBO Gold Member

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                      I have an ammeter and volt gauge.I'll know if sum-ting-wong:rolleyes::lol:
                       
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                      • copper67sat

                        copper67sat Well-Known Member

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                        The ammeter in my 67 functions just as described in post #4. When car is running and everything is functioning normally, it reads just to the right of center - a few amps +. When the alternator is bad it shows a discharge. If the VR starts acting up, the needle bounces a lot. Bad battery usually shows as a heavy charge that doesn't drop off after start up. About the only time the needle is dead on 0 is when everything is off or battery is disconnected. I find it to be a very useful gauge.
                         
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