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How to measure noisy AC

Discussion in 'Electronic Basics' started by Gary Atkins, May 10, 2004.

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  1. Gary Atkins

    Gary Atkins Guest

    My son has a high school project where he has built a simple AC generator
    where the magnets spin, and the coils are static. It will be driven by
    running water from a tank.
    Problem is, he cannot measure the current with his multimeter as the values
    jump all over the place!
    Is there a simple trick to smooth out the power so it can be measured?
    eg a small resistor in the circuit ? Rectify to DC with a diode?
    Any links to generator projects on the web?
    Appreciate any help,
  2. Bill Vajk

    Bill Vajk Guest

    1) Gear drive the alternator so the frequency is driven above/into
    the dampening range of the meter

    2) Put a full wave bridge rectifier on the output and measure
    dc current. However is the frequency (rpm) is very low
    you'll still see severe fluctuatuions. If that's the case, you
    could add enough capacitance to smooth out the meter jumping.

    3) Add more magnetic poles to increase the frequency resulting
    in the same solution as #1, above.

    There may be others, but these spring to mind.
  3. Rich Grise

    Rich Grise Guest

    Is it a digital multimeter? Go ahead and spring $20.00 or so for an analog
    meter - it'll be much more instructive, as you can see the needle move
    in response to the movement of the armature. And you do understand that
    this generator produces AC?

    Have Fun!
  4. One could pull the old bolometer trick. Use the power to heat some
    indicator, such as a small 6V lamp. Compare the power by switching the
    lamp to a power supply to give the same brightness, then use the voltage
    and current of the power supply to give a good estimation of power.

    Ya know, it always bumfuzzles me why Edison insisted on having those
    cumbersome commutators and brushes on his generators.
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