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VFD causing noise

Discussion in 'General Electronics Discussion' started by rasmus, Feb 13, 2018.

  1. rasmus

    rasmus

    30
    0
    Nov 6, 2014
    Hi

    I got a small test rig that i built which is basically a phase converter (single to three phase) which i can use to supply a varying voltage and frequency to various devices... it consists of a three pole motor which is run by a VFD and a three phase alternator... you get idea o_O....

    My problem is with the dc ammeter which has a shunt resistor connected in series with the alternator field coil to measure field current... it runs fine just until the VFD is switched on, when the VFD is switched on, the display that shows the current starts flickering as if the power where being removed and reconnected, As mentioned it runs fine until the VFD comes on, Disconnecting the 2 wires coming from the shunt resistor gets the ammeter back to normal operation but without any current measurement (only voltage). i'm sure this is a noise issue caused by the VFD, isolating the wires from the VFD wires didn't help much, they are all in one panel so i can't get them any further apart then this, lowering the carrier frequency on the VFD did show to be useful but not enough, it still flickers but not as fast as before. Using my oscilloscope i can clearly see noise on the shunt resistor wires that is going to the meter. Any ideas how to solve this problem ???

    the link below show the ammeter i am using with the shunt

    https://www.aliexpress.com/item/DC-50A-Digital-LCD-Power-Meter-Monitor-Power-Energy-Voltmeter-Ammeter-12V-24V/32697593944.html
     
  2. Minder

    Minder

    2,727
    566
    Apr 24, 2015
    What VFD and what is the nature of the motor? 3 pole motor?
    What kind of regulator on the alternator field?
    M.
     
  3. rasmus

    rasmus

    30
    0
    Nov 6, 2014
    Vfd is a Mitsubishi D740 1.5k motor is 3 phase and the field is controlled via a PWM supply that is manually adjusted
     
  4. Minder

    Minder

    2,727
    566
    Apr 24, 2015
    If induction motor, How do you get 3ph 3pole?
    This is not a BLDC or P.M. motor is it?
    M.
     
  5. rasmus

    rasmus

    30
    0
    Nov 6, 2014
    The vfd is a singel phase to three phase... but that is working ok i only have a problem with tbe dc ammeter
     
  6. WHONOES

    WHONOES

    588
    114
    May 20, 2017
    These converters use PWM to create the 3 phases and generally require a specific filter on the output.
     
  7. Alec_t

    Alec_t

    2,546
    672
    Jul 7, 2015
    The ammeter cannot directly read a PWM'ed current correctly. IMO you need to RC filter the voltage developed across the shunt and apply the filtered signal to the ammeter.
     
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