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Thread: Increasing motor speed with VFD for spindle turning on Oliver wood lathe?

  1. #1
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    Increasing motor speed with VFD for spindle turning on Oliver wood lathe?

    Hi there,

    I recently installed a VFD on an Oliver 2159 wood lathe, with 1 hp 3 phase motor.

    I would like to use the VFD to increase the motor speed of the lathe, to slightly increase rpm of the headstock spindle.
    The YFD has a jumper to switch the VFD output from 60 to 120 hertz, so it is an easy adjustment that I have already tested.

    The motor rpm is 1725. The lathe has a reeves drive and the factory high speed is 2800 rpms. I would like to increase that to around 3200-3400 rpms for spindle work. I don't ever plan increasing the speed past say 3400 rpms because it seems unsafe.

    My main question is: will slightly increasing the speed, negatively impact or prematurely wear out the reeves drive?

    and my second question is: will changing the VFD output from 60 hertz to 120, put wear on the motor?

    Any advice would be greatly appreciated.

    Thanks, Andrew

  2. #2
    A VFD is designed to allow you to vary the frequency of the alternating current into the motor. I'm just guessing that the VFD you have will only allow you to vary the frequency between zero (or close to it) and 60 hz.

    I'm also guessing that the jumper you're talking about allows you to vary the frequency to above 60hz, to a limit of 120hz.

    I think what you want to do is set the frequency to some value above 60hz so that the headstock RPMs are greater than 2800 RPM.

    When you modify the input frequency to an induction motor with a VFD, generally the torque remains constant at each RPM, as long as the hz are below the nameplate hz. Since HP is a factor of torque and RPMs, the HP falls as you slow down the motor.

    When you exceed the designed hz, the torque no longer remains constant, but falls. If you think about it, if the torque remained constant, the motor would be putting out more than the rated HP.

    So, yes, you can use a VFD to exceed the rated hz but I wouldn't go too high with the frequency. The motor is designed to operate at a certain max RPM and higher RPMs will put additional stress on the bearings. I probably would not go to greater than 70 or 80 hz. The higher you go, the more stress you'll put on the motor.

    You probably aren't going to use the motor that much - just occasional turning - so I wouldn't worry too much about it.

    Mike
    Last edited by Mike Henderson; 11-01-2017 at 1:00 PM.
    Go into the world and do well. But more importantly, go into the world and do good.

  3. #3
    What about putting a larger pulley on the motor and using the VFD to slow the motor to normal speeds?

  4. #4
    Join Date
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    As Mike said. Remember that when increasing the HZ above 60 you are unable to increase the voltage so the ratio of the two changes. In effect you are starving the motor of voltage. The torque will be reduced and my experience with older motors is they will also run much warmer. Stay within the 70 hz range and don't run for long periods. That size motor will be inadequate with much less torque anyway. A replacement of 2 hp 3450 and dialed down with a vfd might be an option too. Dave

  5. #5
    Mike's got it right.

    I pulled up the manual for the VFD (you put the model number in your other thread), and the jumper sets the MAX frequency (and frequency determines the motor speed). So if you set the jumper to 120 Hz but turn the dial to 50%, your motor will turn at 1725 rpm.

    So, yes, you can do that and increase the motor speed.

    Motors have a "service factor" rating that specifies how much above rated speed they can be run. Look into that, if you're interested, but if this is just for short durations, I wouldn't worry.

  6. #6
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    Feel free to correct me if I'm wrong but if you set 120hz as normal and dial back to 50%, you are assuming the input voltage is 480 in order to get 240 at 50%. I've heard of transforming to 480 to run a 240v motor at 120 using a 480 input vfd and maintaining the torque. It might depend on the vfd type but some clarification would be good.
    Dave

  7. #7
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    Modern small motors are fine up to 200% of rated speed, that may not be true of your Reeves drive.

    You shouldn't have any problem with the small increase in speed you're looking at.....Rod.

  8. #8
    Quote Originally Posted by Dan Friedrichs View Post
    Mike's got it right.

    I pulled up the manual for the VFD (you put the model number in your other thread), and the jumper sets the MAX frequency (and frequency determines the motor speed). So if you set the jumper to 120 Hz but turn the dial to 50%, your motor will turn at 1725 rpm.

    So, yes, you can do that and increase the motor speed.

    Motors have a "service factor" rating that specifies how much above rated speed they can be run. Look into that, if you're interested, but if this is just for short durations, I wouldn't worry.
    You might want to check this, Dan, but I think "Service factor" is the amount you can exceed the HP rating on the motor and have the motor temperature rise by 10 degrees C above nameplate temperature. So if you have a 1HP motor with a service factor of 1.15, you can load the motor to 1.15HP and the motor temperature will rise by 10 degrees C, which will shorten the life of the motor.

    I'm going from memory so check me on that.

    Mike

    [After all, when that induction motor was manufactured, no one was thinking that it would be connected to a VFD. The ratings on the motor are for operation at fixed 60hz (in North America).]

    [Looks like I was wrong about the 10 degree C temperature rise. Here's a better explanation of service factor.]
    Last edited by Mike Henderson; 11-01-2017 at 9:58 PM.
    Go into the world and do well. But more importantly, go into the world and do good.

  9. #9
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    Quote Originally Posted by Andrew Russell View Post
    My main question is: will slightly increasing the speed, negatively impact or prematurely wear out the reeves drive?
    Since you can use the VFD to vary the speed with a potentiometer, I'm wondering if there is any reason to keep the Reeves drive. Could you replace it with two pulleys, sized to give the speed you want?

    JKJ

  10. #10
    Oliver reeves drives are built to last forever, occasional over-speed is not likely to hurt the pulleys or belt. If the motor is original, it is pretty old, not sure that I would worry about it unless the mounting system makes replacement very difficult.
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