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  • 3-phase motor to single-phase?

    There's a Bridgeport mill available in my area with a 1-horse 3-phase motor. I have no capabilities for 3-phase at my location. I do have single-phase 110 and 220.

    Why not just repower the unit with a single-phase 220-volt motor? Does this make sense or is the installation of a phase converter the only route to take? I have no experience of any kind in this area, so your advice is highly appreciated.

    Thanks,
    Johnny

  • #2
    If you have 220-volt available, the best route to go for a single 3-phase machine is a VFD. I got mine from Automation Direct.

    http://www.automationdirect.com/adc/...-Hz_Control%29
    Any products mentioned in my posts have been endorsed by their manufacturer.

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    • #3
      A real good reason is that once you take a close look at the motor in question, you will discover that it is an oddball and a single phase one to fit the mounting will cost you the price of half a dozen VFD's. Do what winchman suggest for less than a couple hundred bucks. You will be proud and welcome to the forum.

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      • #4
        VFD, without a question. Even good ones like Hitachi are so cheap now, that I've been ripping single phase motors out of my stuff, and putting 3 phase motors in!

        allan

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        • #5
          Keep the 3-phase motor. Buy yourself a VFD (Variable Frequency Drive) rated for 1-horsepower.
          The VFD will convert 220 single phase power into 220 3-phase power.
          It also serves as your on/off, speed, and fwd/rev functions.
          You'll love it

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          • #6
            My knee mill is single phase and the motor is heavy, it is also very difficult to change the belt position. Needless to say there is always a strong temptation to run the spindle at whatever speed is already set rather than to match the job.

            How much useful speed variation could I get with a 3 phase motor and a VFD? -50% to +100%?

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            • #7
              Thanks to all. I had not even thought of a VFD and had no idea they were so inexpensive.

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              • #8
                Like everyone else says, run your 3-ph motor with a VFD.
                Why have a perfectly good motor laying around doing nothing? The cost of the VFD will be less than a good quality replacement motor.
                Being able to run a 3-PH motor with single phase is just the tip of the iceberg as far as operating features that a VFD will give you. Smooth ramp up and ramp down, reverse rotation, adjustable overload protection, etc, etc.
                3-phase motors equipped with a VFD is the way lathes, milling machines, and drill presses is should come from the manufacture.
                Home, down in the valley behind the Red Angus
                Bad Decisions Make Good Stories​

                Location: British Columbia

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                • #9
                  How much useful speed variation could I get with a 3 phase motor and a VFD? -50% to +100%?
                  On my lathe with VFD I get -100% to 100%
                  In other words, I can turn it all the way down to zero RPM, and up to 100% of whatever pulley speed I have it set on.
                  I can always go down to zero, but in order to go faster, I need to go up to the next higher pulley.
                  If I'm belted to the fastest pulley, then I have full range of speeds.

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                  • #10
                    My 600V Bridgeport is set up with a cheap 600 to 240V transformer to boost the voltage to a 600V VFD. Works excellent and plugs into a 240V wall outlet.

                    Peter

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                    • #11
                      With my VFD, which does not have the latest bells and whistles for torque at low speeds, I find that the useful lower limit is about 20Hz. If pressed, I have run it at 10Hz but torque is very marginal at such a low frequency. On the high end, 120Hz is no problem. I don't think I've tried going beyond that.
                      ----------
                      Try to make a living, not a killing. -- Utah Phillips
                      Don't believe everything you know. -- Bumper sticker
                      Everybody is ignorant, only on different subjects. -- Will Rogers
                      There are lots of people who mistake their imagination for their memory. - Josh Billings
                      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
                      Don't own anything you have to feed or paint. - Hood River Blackie

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                      • #12
                        I built a power feed unit with a 1hp motor and VFD. On the slow side, I run it at .6 hz which conveniently gives .6 inch per minute. I push a button to give 60 hz for rapids. The motor pulses when using the lowest setting, but not so much that it's a problem with small endmills. At a couple hz, the pulsing is no longer noticeable. This is using an older AC Tech VFD.

                        Wayne

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                        • #13
                          Originally posted by Wayne Sippola View Post
                          I built a power feed unit with a 1hp motor and VFD. On the slow side, I run it at .6 hz which conveniently gives .6 inch per minute. I push a button to give 60 hz for rapids. The motor pulses when using the lowest setting, but not so much that it's a problem with small endmills. At a couple hz, the pulsing is no longer noticeable. This is using an older AC Tech VFD.

                          Wayne
                          Sounds like a great way to cook a motor .

                          The cooling fan will also be doing 0.6Hz....but the current in the coils will be essentially the same as when run at 60Hz.

                          Something to watch for.

                          Rob

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                          • #14
                            Originally posted by MrSleepy View Post
                            Sounds like a great way to cook a motor .

                            The cooling fan will also be doing 0.6Hz....but the current in the coils will be essentially the same as when run at 60Hz.

                            Something to watch for.

                            Rob
                            There's a huge "yabbu" that needs to be examined. Induction motors do not draw nameplate current full time; they only draw the power needed for a particular load. Below a certain load current the motor can dissipate heat without the need for a fan. While that load current is certainly variable motor to motor a light load application like a 1 HP motor intermittantly driving a feed train is likely pretty safe without a fan. But the need for a separate cooling fan really does need to be watched for.

                            YMMV acccording to application of course, but the load/current/duty cycle/ambient air temp/cooling requirements for any motor/load combination have to be assessed before one sweats the need for a cooling fan. A threshold RPM does not automatically indicate the need for supplelental cooling unless the duty cycle is such that motor operating temperatures approach the temp rating for the motor insulation.

                            A biscuit fan zip tied to the motor's fan housing may not be enough. Gotta think it through, engineer style.
                            Last edited by Forrest Addy; 10-15-2013, 06:46 AM.

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