Anonymous
Anonymous asked in Cars & TransportationMaintenance & Repairs · 2 months ago

Does an ammeter measure draw?

I have tried google and all the explanations seem to be for a handheld tool of some kind. I have a 71 Dodge 1-ton and there is a gauge on the dash that says Ammeter. 0 is in the middle of it, with plus and minus on either side. With the key on, radio on etc with the engine off, it goes below the middle, and if I turn more things on, lights, fan, anything else, it goes even lower. With the engine running, it goes above the middle, then settles back down towards the middle after a while- I'm taking this to mean that the voltage regulator is doing its job once the battery is topped off. It's obviously not a voltmeter, and I always said it basically measures draw until someone told me I'm dead wrong and to google it. I understand what the gauge is telling me in regards to my battery, but I'm apparently not putting the right words to it. Thoughts?

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  • Anonymous
    2 months ago
    Favorite Answer

    An ammeter measures current flow. 

    The automotive ammeter basically tells you whether the alternator is meeting the demand of the electrical load of the car. 

    It should always be above "0" if the engine is running.  A little or a lot.  Just above "0".

    It is measuring not only the electrical loads of the vehicle, but the current going to the battery for charging too.

    Think of the ammeter as a CHARGE-DISCHARGE gauge.  The charging and discharging of the battery.

    If the engine is not running, the alternator is not working, so there is no charging of the battery or powering of the electrical load, so the gauge shows discharge.  Discharge of the battery.

    If the engine is running, then the alternator is powering the load and charging the battery.

    You can wire an ammeter differently to show how much current the alternator is generating.  It would not be a center "0" gauge.  It could be 0-30 amps or 0-60 amps or something like that.

    You can have a voltmeter that shows the electrical system voltage.  Ideally, with the engine and ALL electrical loads off, the battery voltage will be approximately 12.6 volts.

    With the engine running, the battery voltage will be approximately 14.4 volts.

    If you understand either of these gauges, you will have an idea if the electrical system is operating properly or improperly. 

    It's not just about the voltage regulator doing its job, but the alternator in general.

    It's nice to have gauges to look at to see what's going on, but many people don't scan them regularly, so if there IS a fault, an unattentive person might not notice.

    If you turn your ignition on but dont start the engine, is there a red light to show there is no oil pressure?  Is there an alternator light to show there is no charging?

    Older vehicles that had gauges, often didn't have any warning lights ("idiot lights") to get your attention.

    Your vehicle likely has a v-belt that turns the water pump, radiator fan and alternator.  If the belt suddenly broke or came off, your charge light (if you had one) would immediately light.  Then your engine temperature would start increasing to the point of overheating.  That might be another light.  But if you have gauges only, then you have an overheating engine that isn't charging the battery.  If you don't scan the gauges regularly, then you wouldn't know anything was wrong, until your engine was cooking!

  • Anonymous
    2 months ago

    Amp meter + its is Charging Amp meter - it is Not charging or discharging 

  • ?
    Lv 5
    2 months ago

    yes it shows you alternator is working properly to charge you battery , also gives you an idea how much power is used by the accesories . you know headlight , aircon , stereo ..

  • ?
    Lv 6
    2 months ago

    Yes, the ammeter measures draw. If current is being drawn from the battery, the needle is below 0. When current is going to the battery, it is charging and the needle is above 0.

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  • Anonymous
    2 months ago

    In your truck it very basically tells you if current is flowing in or out of the battery. It was a stupid idea so in later years it was dropped in favor of a voltmeter which was much more useful if you had half a clue of what you were looking at. Now there's just a warning light. I kind of miss the voltmeter, it was actually useful.

  • 2 months ago

    Do you really think that the ammeter on this truck is worth talking about. They were useless gauges back then and that is why they turned into idiot lights. To keep drivers from obsessing over them like they matter. 

  • 2 months ago

    It measures current flow (Amps). 0 (middle) battery neither charging or discharging.. negative - battery discharging, positive - battery charging. After you start it it should go positive for a bit and settle to the middle once the battery is charged. So, yes, exactly as you thought.

  • 2 months ago

    An ammeter shows the flow of electrical current. When it dips to the left, the car and its accessories are using electricity at a greater rate than the alternator is creating it, so the battery is slowly draining. When you increase the engine revs, the alternator produces more than enough electricity for everything that is running so the ammeter needle moves to the right. When this happens, your battery is being charged by the excess electricity. When the needle sits in the middle, generation and consumption of electricity balance each other out.

  • ?
    Lv 7
    2 months ago

    It measures the current in a circuit. To be pedantic, what you have is known as a zero-center ammeter. Zero-center ammeters are used for applications requiring current to be measured with both polarities, and are commonly placed in series with a battery. In this application, the charging of the battery deflects the needle to one side of the scale (commonly, the right side) and the discharging of the battery deflects the needle to the other side.

  • Anonymous
    2 months ago

    The purpose of the ammeter was to show whether the battery is being charged or is discharging. If the needle is in the middle the battery has a full charge, on the plus side it is being charged, on the minus side it is being discharged because the load on the electrical system is greater that the alternator can currently supply. 

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