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Thread: Using a 3 phase motor to power 3 phase machine?

  1. #1

    Using a 3 phase motor to power 3 phase machine?

    Recently picked up a used wide belt sander for my shop. Only problem is that it is 3 phase and I am on single phase service. Which means that I am going to either need an rpc or a vfd. Will probably go the rpc route that way down the line if I ever get any more industrial equipment I will not have to worry about it. I will have to wait another 4 months or so before I can afford an rpc but I would like to use my sander now.

    I have an older 3 phase motor that is more than two times the power of my sander. Would it be possible to wire this thing up to my sander and use it to generate the 3rd leg? I have a smaller 2 horse pony motor that I could use to start the big motor with. It would be physically unplugged when not in use so I don’t need any complicated switches or even any compactors if I am understanding this correctly. I know that this is not the best way of doing this. But it is only temporary.

    I would like to get advice on how to wire this up as simply as possible.

  2. #2
    Join Date
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    Hopefully you saw this thread a few down from yours.

    https://sawmillcreek.org/showthread....hase-converter

  3. #3
    Join Date
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    And this one https://sawmillcreek.org/showthread....for-Edgebander
    Running today's woodworking machines is much more than just spinning a motor with a DIY phase convertor with dirty power. There are control circuits and circuit boards to consider.

  4. #4
    I’d buy a VFD and use that until I got the RPC going then sell the VFD on eBay when you’re done with it. Think of it as renting a VFD until you can afford the rotary phase converter. It will be much easier than trying to set up a temporary rig and probably less expensive in the long run.

  5. #5
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    A vfd isn't a great solution for a WB. Separate conveyor motor, separate table rise and fall, stop switches all over the place and usually interlocks with pneumatics. Electronics are very complicated. The RPC needs to be sized to handle all three motors. Dave

  6. #6
    Quote Originally Posted by Dan Jansen View Post
    I’d buy a VFD and use that until I got the RPC going then sell the VFD on eBay when you’re done with it. Think of it as renting a VFD until you can afford the rotary phase converter. It will be much easier than trying to set up a temporary rig and probably less expensive in the long run.
    And where would you suggest that I find a budget friendly VFD that will run a 10HP motor and a second VFD for the 2hp feed motor? The second VFD might be cheap but a 20hp vfd would be over $900 at the least.

  7. #7
    Dan, I think your plan to use an idler motor is sound. I have built two of the type of RPC's that use a small motor to spin up the idler. I mounted the starter motor to a hinged board that had an extended handle to tension a v-belt. You start the starter motor while holding the belt tight, spin the idler up to speed, then turn on the main switch, turn off the idler and release tension on the starter. It help if the 2 switches are mounted close to the tensioning handle. It is also pretty simple to use capacitors to start the motor instead. I had a machinist friend who started a 20hp idler by spinning the pulley with his foot.

    The wiring can be as simple as 220v single phase service switch. On the switched side connect to 2 motor leads and continue to sander. Connect another lead from the 3rd motor lead to the sander. Usually, control functions only use one phase, be sure they use the 2 from the power company as the voltage will be somewhat lower on the 3rd leg.

    Do not leave a system like this running unattended. A short loss of power will cause things to burn up if power is restored with the idler well, idle.

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