VFD for Boxford Model A

  1. timangus New Member

    Messages:
    11
    Edinburgh, UK
    My Dad has had a Boxford Model A(UD) lathe that has been sitting in his basement for probably 20 years or so, gathering dust. I've occasionally pestered him to get it running so that he might get a bit of enjoyment out of it, but he's never quite got around to it. It's a 3 phase motor obviously, and while he does actually have a 3 phase supply in the house, extending the wiring to reach the lathe isn't necessarily an easy job.

    I recently learned about the existence of VFDs. This seems like a relatively straightforward way to get it operating on a single phase supply. I was wondering if anybody might have some advice on a suitable unit? It's probably not going to get masses of use so I'm not looking to spend a lot of money; I'm thinking cheap Chinese ebay job rather than bespoke hand crafted German, if you get my drift. Anyway, the motor plate reads:

    Gryphon Brook Motors
    3 phase 1420 RPM
    50 Hz 400/400 Volts
    0.75 HP Type PROT
    1.38 F.L. amps Rating CONT
    50C RISE

    Any advice gratefully received!
     
  2. Pete.

    Pete. Member

    Messages:
    8,674
    Location:
    Kent, UK
    Your motor appears to be single voltage, so not directly compatible. You could open up the motor and split the windings at the star point but it's a bit daunting for many people.

    To get it running I would simply get a long 3 phase lead and run it to the supply. Only needs to be a thin bit of SY cable and small plug/socket.
     
    Seadog likes this.
  3. eddie49 Member

    A VFD running on single-phase 230v AC mains will produce 220v 3-phase, so it needs to connect to a 3-phase motor corresponding to that voltage, which means a motor that can have its three windings connected in Delta. A motor that is in Star or Y mode will need 400v. As Pete says, the plate on your motor only has the 400v rating: 400/400. It should say 220/400. You can confirm the plate by looking inside the motor terminal box. There will only be 3 terminals, you need 6 terminals to be able to convert from Star to Delta.
     
  4. northwest Member

    Messages:
    823
    Location:
    Manchester UK
    This describes the scenario perfectly.
    I would do as Pete says and just get a long 3 phase (4 wire) extension cable. Alternatively, get a replacement motor, they are not that expensive and get it running. A Boxford does not require masses of horsepower.
     
  5. RobCox

    RobCox Member

    Messages:
    63
    Location:
    Cambridge, UK
    daleyd likes this.
  6. timangus New Member

    Messages:
    11
    Edinburgh, UK
    Thanks for the advice everyone, though it turns out I'm an idiot and I mis-transcribed the motor plate! It actually says 400/440. I'm not clear if this changes anything? Here's a (bad) picture: IMG_20200202_205518.jpg
     
  7. Seadog

    Seadog Forum Supporter

    Messages:
    4,779
    Location:
    NE London - UK
    No, it doesn't.
     
    daleyd likes this.
  8. MattH

    MattH Member

    Messages:
    3,655
    Location:
    Bristol
    You can get "dual stage" invertors that input 230v and output 400v.

    They are a little more expensive that a normal invertor but will do the job.

    I used one on a Boxford VSL that @HughF now owns.
     
    eLuSiVeMiTe likes this.
  9. timangus New Member

    Messages:
    11
    Edinburgh, UK
    Okey doke. Thanks again, everybody ;)
     
  10. Wedg1e

    Wedg1e They call me Mr. Bodge-angles

    Messages:
    6,194
    Location:
    Teesside, England
    ...and I use one on my VSL too :D
     
    MattH likes this.
  11. Kram

    Kram Member

    Messages:
    692
    Location:
    Sussex
    AC motors take their rated voltage at rated speed, lower speeds the voltage is reduced and it is roughtly linear, iirc. You'd get about 700-800rpm running from a 240v 3ph inverter without any decrease in torque.
     
  12. m_c Member

    Messages:
    170
    Location:
    East Lothian
    Personally, I'd look at the 240 to 400 inverters. I've just bought one to test on my big mill from AliExpress, but it took a while to get here.
    it's a CNC Weiken brand - https://cnweiken.aliexpress.com/store/group/220V-to-380V-VFD/5248031_516106264.html

    Other Chinese supplier I know people have used is Ecogoo - http://www.ecogoo.com.cn/product-category/220-380 however you need to email them for pricing/ordering.


    This blog from inverter drive supermarket explains this, and what settings you should change in a VFD to achieve it - https://inverterdrive.com/HowTo/240V-Supply-to-a-400V-AC-Motor/
     
    rikrobson likes this.
  13. Hopefuldave Intergalactic pot-mender

    Messages:
    1,151
    Location:
    The Shed of Danger, surrey, England
    I homebrewed/hacked my own 240 to 415 VFD, started with a secondhand ABB 3-phase 415-input VFD and did a modification that cost about 20p*, nowhere near the difference you pay to have an inverter seller do precisely the same mod... It gives the full frequency and speed ranges and full power you'd get from "native" 415v, downside is the main bus capacitors age prematurely and give you regular Under Voltage alarms at high loads when it's time to change 'em (about £20 if you shop around, takes a year or so with heavy use, a few with hobby use).

    It does invalidate all warranties and the CE and UL approvals though, and probably causes Gerbil Warming...

    Dave H. (the other one)

    * conversion of the mains input to a voltage doubler circuit, 4BA brass bolt and nuts, ring terminal, some solder and iron and a hole drilled in the PCB copper between the two banks of bus capacitors, easy peasy BUT needs a VFD that won't panic at seeing a missing phase and has two banks of capacitors in series to make the necessary voltage rating (1980s - 90s ABB ACS300 are perfect).
     
    daleyd likes this.
  14. duncans Member

    Messages:
    75
    Location:
    leicester
    shame as I've got a brand new one in my shed it's a Chinese one I ended up getting it free as wasn't the same one as in the advert and he didn't sent me a return label 1st thing I've ever got free off eBay Screenshot 2020-02-19 at 07.14.27.png lol
     
  15. Hopefuldave Intergalactic pot-mender

    Messages:
    1,151
    Location:
    The Shed of Danger, surrey, England
    Have you taken the lid off the junction box on the motor (assuming it has one)? If there are 6 terminals in there, 3 with the incoming wires and 3 linked together, it's a dual-voltage motor and can be re-linked for 240v 4-phase - quite common, as Merkins in the Rebel Colonies use 220ish 3-phase and Boxford exported to them. If so, you can use the cheap 240v VFDs no problem (well, none from the motor, anyway).

    Dave H. (the other one)
     
  16. hareng Member

    Messages:
    1,485
    Location:
    Wolverhampton
    Change the motor theres every chance its had it or on the way out needing a rebuild. Had exactly that on a 2.2kw Brook Compton 400v 3ph, took loads of power to start up could only run it at 370 - 540 rpm with a push start from a 7.5kw invertor.
    Bought a new motor 2 1/2 years ago installed last year but didnt fit the Mitsubishi VFD until last year. Same Invertor 7.5kw kicking out 3ph 400v not a problem on startups but weiry when gearbox set for 1800+ rpm - 7.5kw + 60% for 10 secs took with a small 5 1/4" chuck in excess of 10 secs to 2500 rpm.
    18 months later control board contactors went down, easiest convert to VFD and swap motor to 220v with Mitsubishi bought. Got no power even with 3mm cuts its throwing 13A on the display and spindle slowing. Yet supposedly ok for the job.
     
  17. Hopefuldave Intergalactic pot-mender

    Messages:
    1,151
    Location:
    The Shed of Danger, surrey, England
    Sounds like duff bearings, only a few quid to replace and an afternoon's work, if that. I have a7.5 HP Western Electric in my phase convertor, that would pop breakers all the time until I noticed that it barely turned by hand, changed the bearings and it's fine now...

    Dave H. (the other one)
     
    daleyd likes this.
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