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  1. #1
    Hi Guys
    The single phase motor on my Emcomat 7 has a burnt coil, i tried a local rewind service but they have a huge backlog so can't rewind it.
    They also wanted 700(estimated) plus vat.
    Spares are almost non existant for my lathe model, but i was fortunate enough to find a three phase motor in the Netherlands. the bearings were wrecked but i have replaced them. the windings show no sign of overhaeting so just fingers crossed that it is going to work.
    So could anyone point me in the direction of a suitable converter that will convert single phase to three phase and boost the voltage to the required 380V.
    Would it run off 220V three phase.

    Motor info
    Type 80A/2/4SM
    380V /1.3 /1.3 A
    0.45 /0.3 Kw
    2800/1400 rpm
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by mekanik; 13-04-2023 at 02:27 PM. Reason: couldn't attach file

  2. #2
    From the plate this seems to be a 2 speed motor, that is, wound as a 4 pole but the windings switchable to run as 2 pole at double the speed (i.e. 1400 & 2800 rpm). If the star point is accessible you could change it from star (380v) to delta (230v) running, though I think that's a bit trickier with a 2-speed motor. You could also run it from a lower voltage 230v inverter anyway, it will run at whatever speed is selected but just give a bit less power. Apparently if you actually reduce the speed to about 30Hz you can get the same power. Inverter Drive Supermarket sell drives, possibly 230v in 380v out ones, and they also have a note on their website about running at lower speed. Find them with Google.

  3. #3
    Hi John
    Thanks for your prompt reply. Yes it is 2 speed done with a mechanical switch. manual shows single phase and three phase link up. is that delta config.
    Have attached a copy of the 3 phase wiring that i got when i first bought the lathe, the recently purchased motor is Emco specific but don't know if it's same as shown in the circuit diagram.
    will check out your link, What size (Kw) would be required?
    will try and get a photo of the wire colours on the 3 Phase motor if that helps.
    Kindest Regards

    Click image for larger version. 

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    Last edited by mekanik; 13-04-2023 at 05:27 PM.

  4. #4
    Bizarrely the lathe motor has delta windings and the mill head star!

    But the real question is what the winding config is on your new motor. Is there a connection cover you can remove and get a photo of it? If it can be easily converted to delta then the neutral, the place where all the windings are connected at one end at the centre, would be accessible at screw terminals and/or have links.

    The rating plate says it's 0.45kW 2-pole (2800 rpm) and 0.3kW 4-pole (1400 rpm) so a VFD rated at 750W (0.75kW) should be fine.

    Fitting a VFD it is best to scrap all the switchgear between the VFD and the motor, you shouldn't be tempted to switch the motor when running with an existing contactor, it will instantly blow up the devices in the VFD. All the control can be done by the VFD - start/stop, speed, reverse, soft start, e-stop etc. Just need an isolating switch and filter where the mains comes in, and a control pendant.

    I've fitted 3-phase to a couple of mills using standard delta motors with ordinary VFDs and also fitted a Newton-Tesla pre-packaged unit to my Super 7 - but I haven't any direct experience of 2-speed motors. It can't be that hard though. With a VFD I doubt you would want the 2-speed feature anyway as the VFD does it for you.

    I have heard that these people are very helpful: https://inverterdrive.com/

  5. #5
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Current Activity: Viewing Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,915. Received thanks 360 times, giving thanks to others 8 times.
    2 speed motors are rarely dual voltage.

    You can run a 380V motor from a 240Vout VFD, but you lose torque above 27Hz (IIRC! -Inverter Supermarket have a blog article explaining it) as the motor enters into constant power, rather than constant torque due to the restricted voltage.

    However, 'boost' VFDs are not that expensive or rare now. I've personally used a few CNCWeiken boost VFDs - https://www.aliexpress.com/store/gro...000324416.html
    But others have used Ecogoo.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  6. #6
    Thanks John/mc
    That unfortunately is a problem for me, in turning mode the VFD control would be fine but for screw cutting i really require the button arrangement. i have seen inverters were the control panel detaches and presumable could be extended with a cable and mounted on the headstock so i suppose it is possible. a rotary converter is just overkill for one machine, perhaps it's back to getting the single phase motor repaired.
    Does the 700 sound excessive for a rewind ?
    Thanks again Guys.

  7. #7
    as you can see no terminal connections.
    any ideas on how you would connect to the VFD ?
    MC if you get time could you possibly send a picture me of your control system, no rush i still have to fathom a mounting arrangement fot the motor, it doesn't have the usual flange mount.

    Click image for larger version. 

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  8. #8
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Current Activity: Viewing Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,915. Received thanks 360 times, giving thanks to others 8 times.
    I'd probably wire it up to make use of the low speed, then set the VFD to allow a higher frequency to get the high speed back.
    With the correct VFD, you can configure it to allow the use of a Jog button.

    Out of the three boost VFDs I have, one runs my rotary converter, one runs a basic saw, and the other is destined for my big mill which is very slowly getting bits added to it, but will likely be getting controlled via ModBus.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  9. #9
    Have been watching Youtube this afternoon and apparently the Delta arrangement allows the motor to run on 220/250V.There was a guy had a system of using the original switching, but i will have watch that a couple more times to get my head round it.
    Also fathomed out the rather strange motor mounting arrangement.

  10. #10
    700 sqids could buy a brand new 3phase motor and vfd!

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