How do I connect a 2 lead automotive 60 Amperes Gauge directly to an alternator?

Discussion in 'Automotive Electronics' started by aleggert52, Jan 6, 2016.

  1. aleggert52

    Thread Starter New Member

    Jan 6, 2016
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    I am using a 7.5 HP gasoline engine with an alternator attached to that I made to help charge banks of batteries that I use to power my house on an island with no electricity. The problem that I am having is how to connect the ampere gauge to the unit to see how many amps it is charging at. I bought the alternator at a parts yard and it does not have any markings saying the output of the amperage. Would appreciate anyone who can help me connect the gauge to the alternator. I don't know if I need a shunt or not?
    Thank you,
    aleggert52
     
  2. crutschow

    Expert

    Mar 14, 2008
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    What does the gauge look like?
    What does it say on the gauge face?
    Cant' tell if it needs an external shunt without more info.
     
  3. aleggert52

    Thread Starter New Member

    Jan 6, 2016
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    it's a round automotive gauge the face reads plus and minus 30 to 60 amperes. it has 2 posts on the back one is plus the other is minus. the manufacturer is F.D of Japan. I was told the gauge connects to the positive and negative leads on the alternator but that does not work. Any recommendations would be appreciated.
     
  4. BR-549

    Well-Known Member

    Sep 22, 2013
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    aleggert52, unfortunately, we can't see through your eyes.

    We will need a clear photo, or a data sheet, or a link for that gauge.
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    It should connect in series with the charging wiring not across it...IF it has an internal shunt.
    Check this by using a multimeter on the lowest ohm scale. Read between the posts on the meter. If it shows a zero or extremely low reading then the shunt is inside the meter.
    If not you need a shunt.

    To use it put the post labeled ( - ) on the negative lead from the alternator. Connect the positive post to the portion of the negative lead going to the battery. DO NOT connect the positive cables to this meter. Put it in the low side for safety.
    Recap: negative wire out of alternator to negative post of meter. Positive post of meter connects to cables going to negative post of battery. This puts the meter in series with the charging current. If it does not have an internal shunt this will destroy the meter
     
  6. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Automotive amp meters are usually installed in series between alternator and battery.
    output.png

    Kermit2 beat me, but he also mentioned a shunt, which I didn't think about, which you might have. Best thing to do is let us know exactly what you do have...
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If you connected it in parallel with the alternator output (instead of in series with the alternator and a load) the gauge may now be dead :(.
     
  8. aleggert52

    Thread Starter New Member

    Jan 6, 2016
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    All I know is the Ampere Gauge is new. There is no data sheet or installation instructions. The 2 post on the back are marked "+" and "-". I have a similar AMP gauge in my sailboat with two posts as well with different markings, the "Batt" post goes to the positive post on the alternator and the "ICO" or the other post on the AMP gauge goes to an engine ground. Could this be the configuration that the new AMP gauge needs to work? The new AMP gauge does not respond to connecting it to the low side"-" in series. Nothing happens when the alternator is running.
     
  9. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    So might the alternator...
     
  10. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Have you checked the ammeter with an ohm meter as I suggested? What was the resistance between the two binding posts?
     
  11. aleggert52

    Thread Starter New Member

    Jan 6, 2016
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    It appears to have a built in shunt. on the ohm meter lowest setting I get a reading of about 14.0 ohms. I have tried testing in series on low side, high side, parallel and I simply cannot get the meter to work. I have not hardwired the AMP gauge in any of these tests to keep from burning it up, it just does not work and I do not know why at this point. I am beginning to think that it might have been defective when I bought it. The alternator is charging good 14.5 volts and each battery responds with a good charging rate in voltage. when I connect the batteries it puts a load on the 7.5HP motor so I know that good amperage is present. I just wanted to have a ballpark amperage that the alternator is charging at, but so far that challenge has not been met.
     
  12. crutschow

    Expert

    Mar 14, 2008
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    14 ohms is way too high for a shunt resistor. That would only allow a fraction of an amp to flow when it is connected in series with the alternator and connected to the battery.
    A shunt for 60A would be a small fraction of an ohm (look like a short to an ohmmeter).

    So you need to find more out about the ammeter.
    Do you have a variable DC supply available?
    You need to supply a small voltage to the ammeter to determine how much voltage will give a full scale reading.
    From that the correct value for the external shunt resistor can be determined.
     
  13. aleggert52

    Thread Starter New Member

    Jan 6, 2016
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    Thank you for the ohm information. I will try what you recommend.
     
  14. pbr333

    New Member

    Jan 22, 2012
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    Hey if the amp meter gauge has a brand name on it we might be able to google some specs for it ? Also if it is Automotive
    specific gauge with large (5 or 6 mm) terminal posts on it its probably meant to be installed inline with current flow(which is a
    connect and go-no instructions needed). If was designed to work with a shunt on a car, that would be manufacturer specific
    and include connect instructions to obtain an accurate reading.
    Another quick way to solve your dilemma would be to pick up a cheap test meter that has inductive clamp amp meter with a
    range of 1-400 amps. I have a local store here that has them for about $14.00. I hope this helps.

    pbr333
     
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