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  1. I have an HSD spindle which I plan to use on my VTX1 rebuild, it is rated at 5Kw 380v 2 pole 400hz. I am running it on a vfd at 240v at the moment.

    I am looking into the possibility of getting it rewound as ~ 3Kw 240v 8 pole 400hz. I think this would run at more suitable speeds for a mill and have more torque at the lower speeds. My VFD will actually go to 1000hz so could still get~ 18000rpm.

    Perhaps even a pole changing winding, though I am not sure how the VFD would cope with that.

    Has anyone gone down this path - what are the snags etc - there are always some

    I did note from a search that John S had dabbled a little in rewinds.

  2. #2
    Did you get a price for a rewind ? it might be best to sell the one you have and buy another with the correct parameters you need.

  3. Haven't got as far as pricing yet, just exploring the possibilities at the moment but, even if I found a spindle with those specs, I think the price gap between selling and buying would be a lot more than a rewind.

    It's a 24 slot stator so an 8 pole single layer winding is simple and well within DIY territory
    Last edited by johnsattuk; 25-12-2013 at 11:54 AM.

  4. #4
    Ok need to get better advise on this after the holiday but don't think a 2 pole can be changed into an 8 pole just by winding.
    OK the stator has 24 slots but the rotor has to match.

    Also at 8 pole you will get approx 5.700 revs at 400 hz and there will be a limit you can go to on hz before it all gets saturated or egg bound in technical terms.
    One guy on another forum has just had a quote for a standard 3~ rewind at 350 I can supply him a new motor for 125
    John S -

  5. Ok need to get better advise on this after the holiday but don't think a 2 pole can be changed into an 8 pole just by winding.
    OK the stator has 24 slots but the rotor has to match.


    Is there an easy way to find out the slots/bars in the rotor, the laminations are ground smooth and appear continuous, it is 58 dia x 130 long, the stator is 108 o/d

    Also at 8 pole you will get approx 5.700 revs at 400 hz and there will be a limit you can go to on hz before it all gets saturated or egg bound in technical terms.

    Can't find the specs for my exact motor but HSD do give figures for their 4 pole motors to 28000 rpm (933hz). It is 5 Kw continuously rated so I was hoping that derating to ~3 Kw would give a bit of headroom. Because its a mill I am more interested in some low speed torque than high speed, I think ~6000 rpm max would be OK

  6. #6
    Duplicate post, please ignore this one.
    Last edited by EddyCurrent; 25-12-2013 at 04:22 PM.

  7. #7
    I don't know exactly which motor you have but can you change the connections from star to delta ? it won't change the number of poles obviously but it would give a lot more torque. I've worked with motors for a long time and have never heard of rewinding an ac motor being described as, "simple and well within DIY territory".

  8. Quote Originally Posted by EddyCurrent View Post
    I don't know exactly which motor you have but can you change the connections from star to delta ? it won't change the number of poles obviously but it would give a lot more torque. I've worked with motors for a long time and have never heard of rewinding an ac motor being described as, "simple and well within DIY territory".
    My first thought was to look the at connections to see if I could reconnect as delta . The motor windings are well constructed with every thing tightly wrapped up varnished and baked, I don't know if it is star or delta at the moment and it would take a bit of risky digging to find out.

    I have also worked with motors for a long time, I have in the past (~60 yrs ago) rewound the odd motor or two, things had not used to be so throwaway then, I also had the advantage of working at a motor manufacturing plant, so all the materials were readily available.

    The actual laying in of the coils is a fairly easy mechanical task, particularly with 8 poles 24 slot single layer, and is well within my DIY territory.

    The more technical aspect of rotor slots, flux densities,wire gauge and turns is a bit more challenging, as John S inferred, which is why I was looking for the experience of others who may be designers of motors. There are several programs available to help with this but was looking/hoping for a shortcut.

  9. [QUOTE=EddyCurrent;52560]I don't know exactly which motor you have but can you change the connections from star to delta ? it won't change the number of poles obviously but it would give a lot more torque. .[/Q

    Changing star to delta connections will change the operating voltage and ~ double the amps required, doesn't change the torque curve of the motor.

    More torque will require even more amps, which I haven't got, or more poles. This is in my garage on a 240v supply with my existing 3Kw VFD which is why I am looking at changing pole count.

  10. Update

    I have eventually rewound my 2 pole spindle to 8 pole, dragged on a bit for a variety of reasons. Did a little research on rotor slot numbers, seems to be a bit of a black art with different motor manufactures doing their own thing, seems to be more to do with starting torque and efficiencies than any thing else.

    Invested in a winding design service on the net, asked for 240v 400Hz delta connection, came up with 20 turns per slot.

    Wound the stator at 20 turns two in hand 0.75mm wire, ~20A in delta no load running - ~12A in star, this was about 8 times the original motor.

    Some emails back and forth getting me nowhere, seemed obvious to me that it was lack of turns (flux).

    Decided to think it through on the basis that I knew the turns and current of the original motor and that HSD had got the ampere turns right.

    Fortunately I had tried the motor before varnishing it so I was able to strip it down again very easily.

    Wound the stator at 50 turns two in hand 0.55 wire, ~2.5A in delta no load running similar to the original motor, runs OK up to 500Hz which is more than I want.

    From when I was a young lad my Father repeatedly told me ' Beware the Expert'

    Not particularly neat but does the job OK


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