Help me interpret my motor plate and other VFD questions
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  1. #1
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    Default Help me interpret my motor plate and other VFD questions

    I know this has probably been covered before but I've been searching and reading for awhile and am still somewhat confused. Sorry if folks are tired of answering VFD hookup questions but here goes.

    The motor on my mill is a 2 speed single voltage (220V) motor. I've installed and run a VFD on a similar motor before and followed the general advise of "just hook it up to the high speed windings". It worked fine for what I needed but have to admit I never ran that mill very hard. This is another mill and I'd like to come to a greater understanding of the compromises in using a VFD for phase conversion. I'm currently running it on a (noisy) rotary phase converter but would like to be able to reverse the motor and eliminate the bulky electrical cabinet.

    So here's the motor plate


    If I'm reading it correctly I get the following values

    RPM-----825------1640
    Amps---4.25------6.2
    KW------0.90------1.5
    PF-------0.80------0.92

    It seems a bit strange that it is wired in delta for low speed and Y for high speed as this seems opposite of what I read is the usual. Is that the case?

    Using this on-line calculator I get 1.56hp at low speed and 2.62hp at high speed. I believe that the loss of horsepower due to the VFD is linear so I should see 1.31hp at 825rpm with a VFD running at 30hz. If this is correct, I am losing .25hp by using the VFD to slow the motor to 825rpm rather than using a contactor to switch the windings.

    Am I understanding this correctly?

    My other questions are about the brake data plate. I'm assuming this is a braking resistor that I can hook up to the VFD (eg. an Automation Direct GS2) and get 80 ohms additional of dynamic braking. Is this correct?

    Thanks for any help

    Teryk

  2. #2
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    Quote Originally Posted by mTeryk View Post
    I know this has probably been covered before but I've been searching and reading for awhile and am still somewhat confused. Sorry if folks are tired of answering VFD hookup questions but here goes.

    The motor on my mill is a 2 speed single voltage (220V) motor. I've installed and run a VFD on a similar motor before and followed the general advise of "just hook it up to the high speed windings". It worked fine for what I needed but have to admit I never ran that mill very hard. This is another mill and I'd like to come to a greater understanding of the compromises in using a VFD for phase conversion. I'm currently running it on a (noisy) rotary phase converter but would like to be able to reverse the motor and eliminate the bulky electrical cabinet.

    So here's the motor plate


    If I'm reading it correctly I get the following values

    RPM-----825------1640
    Amps---4.25------6.2
    KW------0.90------1.5
    PF-------0.80------0.92

    It seems a bit strange that it is wired in delta for low speed and Y for high speed as this seems opposite of what I read is the usual. Is that the case?

    Using this on-line calculator I get 1.56hp at low speed and 2.62hp at high speed. I believe that the loss of horsepower due to the VFD is linear so I should see 1.31hp at 825rpm with a VFD running at 30hz. If this is correct, I am losing .25hp by using the VFD to slow the motor to 825rpm rather than using a contactor to switch the windings.

    Am I understanding this correctly?

    My other questions are about the brake data plate. I'm assuming this is a braking resistor that I can hook up to the VFD (eg. an Automation Direct GS2) and get 80 ohms additional of dynamic braking. Is this correct?

    Thanks for any help

    Teryk
    So you have what is called a "Dahalnder Motor", a way of doing 2 speed motors which, in this case, is resulting in a roughly 2:1 speed change and (other than a change in PF), relatively constant torque. Your machine likely works on torque, and that's what VFD does; reduces speed while MAINTAINING torque. That's what you want here. Don't get hung up on HP values, it's torque that counts. So yes, connecting it in high speed and varying the frequency will give you the same thing.

    FYI it is going from Delta (low speed) to YY (high speed) by changing the number of poles. In going from high to low speed, the two parallel sets of Y windings are reconnected in series and a Delta pattern, so you go from 4 poles to 8 poles which cuts the speed in half.

  3. #3
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    Quote Originally Posted by Jraef View Post
    So you have what is called a "Dahalnder Motor", a way of doing 2 speed motors which, in this case, is resulting in a roughly 2:1 speed change and (other than a change in PF), relatively constant torque. Your machine likely works on torque, and that's what VFD does; reduces speed while MAINTAINING torque. That's what you want here. Don't get hung up on HP values, it's torque that counts. So yes, connecting it in high speed and varying the frequency will give you the same thing.

    FYI it is going from Delta (low speed) to YY (high speed) by changing the number of poles. In going from high to low speed, the two parallel sets of Y windings are reconnected in series and a Delta pattern, so you go from 4 poles to 8 poles which cuts the speed in half.
    Thanks for the response. Wasn't aware of dahlander motors. That explains a few things. By my reading of the motor plate, I think the motor actually has more torque at the lower speed than at high. I think if I decide to go with a VFD, however, I'll go the simple route first and simply wire it to the high speed windings. If I find the loss of torque detrimental, I'll put contactors in between to switch the windings.

    Doing a bit more research on the brake issue reference in my OP, I'm guessing that the brake referenced by the data plate is a DC injection brake. Need to do a bit more research into how to use that with a VFD..... or whether I need to.

    Teryk

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    Hi Teryk -

    I am curious how this worked out for you? I am installing a Deckel FP-1 in my single phase garage. The FP-1 shares the Dahlander motor that you have and I am considering the GS2. Could you please let me know how this ended up? I would hate to go down this road if you had problems.

    Thanks in advance - DVR

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    Same configuration as the AEG motor on my Emco Super 11.

    -Dave

    img_4469-copy.jpg

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    Quote Originally Posted by bigwave View Post
    Same configuration as the AEG motor on my Emco Super 11.

    -Dave

    img_4469-copy.jpg
    Thanks Dave!


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