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  1. #16
    Join Date
    Sep 2012
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    Hi Greg,

    I can answer your question as to why the motor ran before and why it wouldn't later !

    ANSWER:
    There was enough stray magnetism in the rotor to cause the motor to turn without any load on it. If you had a load, such as a belt connected the motor wouldn't have even turned. When you reconnected the power and retested it, the AC field removed the residual magnetism. The motor would have rotated in the first instance even if the wiring was wrong, simply because there was enough residual magnetism to react with the magnetic field created due to the applied voltage in at least one of the windings.

    The residual magnetism was caused by the supply voltage being removed when the current through one of the windings was at its peak.
    Best Regards:
    Baron J.

  2. #17
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by BaronJ View Post
    Hi Greg,

    I can answer your question as to why the motor ran before and why it wouldn't later !

    ANSWER:
    There was enough stray magnetism in the rotor to cause the motor to turn without any load on it. If you had a load, such as a belt connected the motor wouldn't have even turned. When you reconnected the power and retested it, the AC field removed the residual magnetism. The motor would have rotated in the first instance even if the wiring was wrong, simply because there was enough residual magnetism to react with the magnetic field created due to the applied voltage in at least one of the windings.

    The residual magnetism was caused by the supply voltage being removed when the current through one of the windings was at its peak.
    My understanding was he was trying to start the mill (ie under belt load etc) with the motor left on the Hi-V (415/440V) configuration.
    If so the motor even under a slight load may simply not generate enough torque at low RPM to start.
    From then on it depends on the VFD, some VFDs persist and increase V/I until the motor starts, some just give up and stay at zero RPM, some report an error.

    A similar thing applies when a correctly configured motor has a locked rotor/spindle . The Powtran VFDs I'm using on the mill and lathe simply stay at zero RPM.

  3. #18
    Join Date
    Aug 2015
    Location
    Melbourne, Australia
    Posts
    843

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    BaronJ, thanks. This electrickery is fancy stuff. There is a hole in my head where electrical knowledge falls out. One of those things that just never seems to stick. If your explanation above can explain why it worked incorrectly wired then great. Happy. )

    Bob, it wasn't in Hi-v (as described by diagram), it was kind of neither hi or lo I guess. The way I had it was 9&3, 8&2, 7&1 joined (as per lo-v diagram) but power going separately to 4/5/6 which were not joined into one. So I had the power going to the wrong place, and 4/5/6 were not joined.

    Still. Damn thing 'worked' like that so it fooled me. Glad I didn't let the smoke out.

    Greg.

  4. #19
    Join Date
    Jul 2018
    Location
    United States
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    72
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    Did you leave the forward and reverse switch in the circuit? You may have toasted the VFD by switching on and off at the switch and not using the F/R commands on the VDF. The frequency output may is weak, a VFD varies the frequency. The mosfets may be toast and putting out very little therefor no torque under load. Another though do you have the parameters set for the motor?
    Jack

  5. #20
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by machinejack View Post
    Did you leave the forward and reverse switch in the circuit? You may have toasted the VFD by switching on and off at the switch and not using the F/R commands on the VDF. The frequency output may is weak, a VFD varies the frequency. The mosfets may be toast and putting out very little therefor no torque under load. Another though do you have the parameters set for the motor?
    Don't worry - its all working fine.

  6. #21
    Join Date
    Aug 2015
    Location
    Melbourne, Australia
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    Thanks Jack, as Bobs says, all good now. The issue was me not wiring it correctly. ) Doh.

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