Spindle motor rewind

[John S]

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

[johnsattuk]

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

[EddyCurrent]

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".

[johnsattuk]

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.

[johnsattuk]

[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.

[johnsattuk]

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

[Clive S]

Very interesting John, Just goes to show with knowledge and patience a lot can be achieved ..Clive

[GEOFFREY]

Brilliant, well done. I don,t suppose that you want to rewind my HF (1000hz, 55volt) to 400hz 230volt), for a (small) bag of gold of course. This is a serious enquiry as I too have been told that it is not possible. G.

[johnsattuk]

I don,t suppose that you want to rewind my HF (1000hz, 55volt) to 400hz 230volt), for a (small) bag of gold of course. This is a serious inquiry as I too have been told that it is not possible. G.

Sorry but modifying some one else's motor would be a bit scary , I persevered with mine mostly because I was told it's not possible and I could see no reason that it could not be done, just a matter of finding the correct info, I have spent a lifetime solving engineering problems, many of which were not possible.

There are motor design programs out there but they are very expensive, need to find a friendly face in one of the universities. I tried a couple of re-winders for info but they really don't want to know about anything non standard.

Modifying an existing motor should not be too difficult if you accept that the manufacturer got it right with respect to flux densities in the stator (ampere turns in old money).

This something I found somewhere on the net.

Rewinding for a change in voltage

If a 220 volt motor is to be rewound to operate on 440 volts, use twice as many turns on each coil and one-half the circular-mills area of wire. In other words, if 40 turns of NO. 17 wire were used on the original motor, 80 turns of NO. 20 should be used on the new motor

Some motors rated for 230 volts will not handle the load on 208 volts if loaded to the maximum. The turns must be reduced to the ratio of the voltage change. As an example, 230-volt motor has 40 turns: 230/208 = 1.1, 40 turns/1.1 = 36 turns. If there is enough room, the next larger wire size should be used. An easy way to determine whether there is enough room is to cut the required number of of lengths of wire of this size and fit then into the slot.

Changes for New frequency

There are two ways to convert these motors; one keeps the same horsepower for the new speed, and the other keeps the same torque for the new speed (more horsepower). For the same horsepower, use the following formula: old turns*Sqrt(old Hz / new Hz) = new turns. If you want the same torque then it is: old turns*old Hz/new Hz = new turns.

[Sourabhkumawat]

Can you share your email? I would like to do this modifications too. Just a couple of questions. 😅 My mail is [email protected]