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DC Motor Speed

Discussion in 'General Electronics Discussion' started by coryroth, Jul 8, 2019.

  1. coryroth


    Jul 8, 2019
    Have gotten stuck on a problem at work. I have a small DC motor (specs: 6,000rpm, 1.5v, 220mA, 3-pole) located, inside of a product and have no visual access to. The only thing I have access to are the positive and negative terminals. Question is, how the heck can I measure the estimated RPM of the motor without cracking the item open? I've read a few ways here and there, but it's all over my head. I've tried reading the frequency with a multimeter, but that comes out to about 8kHz which can't be right.

    Any help or pointers would be awesome!
  2. Audioguru


    Sep 24, 2016
    If the motor vibrates slightly because it is out-of-balance then it will produce a hum sound. If it spins at 6000RPM then the hum will have a frequency of 100Hz. Use a microphone that feeds an audio amplifier and measure the frequency with your multimeter.
  3. Alec_t


    Jul 7, 2015
    Connect a low-value resistor in series with the motor as a current sensor and check the voltage across the resistor with a scope. If it has a periodic component, that will be related to the rpm.
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