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Using AC current meter to measure DC current?

Discussion in 'Electronic Basics' started by Tibur Waltson, Dec 30, 2003.

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  1. DC current meter could measure DC currents. But is it possible to use a DMM
    AC current meter (rated 1-1000A) to measure current draw on an alternator's
    DC output to see if it could put out 30A on a Honda automobile?
  2. I assume you are talking about a clamp around AC ammeter. If so,
    these produce a reading by transformer action, which does not work for
    DC. If you want ot read the DC current in some conductor you might
    try to borrow a hall effect amp meter from someone. These do respond
    to the magnetic field of DC.

    You would probably do better with a 50 amp, 50 millivolt shunt
    resistor wired in series with the alternator, with a millivolt meter
    connected to infer the current each millivolt represents one ampere).

    You may find one of these or the hall effect clamp on meters for a
    reasonable price on EBAY.

    You will also need some sort of load bank of big, low value resistors
    to connect across the alternator, to bring the current up till the
    voltage starts to sag to find out its capability at a given RPM. 13.4
    volts divided by 30 amps is a resistance of about .45 ohms rated for
    400 watts. This is something like a few yards of iron fence wire
    dipped in a bucket of water with a big alligator clamp that can be
    moved to adjust the current.
  3. ddwyer

    ddwyer Guest

    moving iron ammeters measure DC current
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