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measure current drawn while using pulse width modulator?

Discussion in 'General Electronics Discussion' started by Madsalts, Jul 28, 2015.

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  1. Madsalts


    Sep 25, 2014
    I have a motor hooked up to a pulse width modulator. How would I measure current draw at partial duty? At 100%, it's easy enough. I don't have an oscilloscope, so I can't determine the pulse width at a given setting. If I am at a duty percentage less than 100%, and I take a current reading, how would I interpret the results? I have an analog meter, btw. I imagine the current reading on the meter would be a good approximation of what I'm actually drawing, or would it? Thanks.
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The analog meter should give you something approaching the average current. If you multiply that by the inverse of the duty cycle you'll get the peak current.

    This can be confirmed by replacing the motor with a resistor and ensuring that the average current measured by your meter is proportional to the duty cycle.
  3. Madsalts


    Sep 25, 2014
  4. Minder


    Apr 24, 2015
    The current waveform does not generally represent the voltage waveform, it is a mean level saw tooth in nature.
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