Spindle motor rewind

[Jonathan]

There are motor design programs out there but they are very expensive

Here's a free one:
https://www.emetor.com/
Although lately I've been using this one as it's on the university computers.

Anyway, Geoffrey, have you got a picture of the stator inside your motor? I'd be interested in rewinding it / working out how for you. Who told you that it wasn't possible and what reason did they give?

[johnsattuk]

Here's a free one:
https://www.emetor.com/
Although lately I've been using this one as it's on the university computers.

I did find and play with emetor and also Koil, and some demo versions of others, but really my only requirement was no of turns per slot and I did not find that these gave me that info.

I originally tried the forum in the hope that some kind soul would help with some positive info.

It is highly unlikely that I will wind another motor, this was a just a whim that became a challenge.

[GEOFFREY]

Here's a free one:
https://www.emetor.com/
Although lately I've been using this one as it's on the university computers.

Anyway, Geoffrey, have you got a picture of the stator inside your motor? I'd be interested in rewinding it / working out how for you. Who told you that it wasn't possible and what reason did they give?

Thanks for your reply and offer Jonathan. I do not have any pictures of the internals of my spindle as I have never thought about dismantling it. I have a couple of these spindles which I love to use because of the air release collet chuck and work around the fact that I am limited to 3.172mm shank tools. As I have a "spare" spindle I would be happy to take a chance that it does not work if you are prepared to try. The impossible comment came from various commercial rewinders and I had very little faith in that I believe that nothing is impossible!!! Perhaps a little difficult sometimes. The most logical comment came from one rewinder who said that it would be difficult on a small diameter spindle to use the heavier duty wire necessary to change. These spindles are lovely (ex pcb machine), but I only have one HF inverter and I would like to get one running on a standard 400hz inverter as I have started to strip down another machine which has a cutting area of 540x600mm. G.

I apologise if I seem to be hi-jacking this thread, but I did start a somewhat similar thread about my spindle and had no response. G.

[johnsattuk]

The most logical comment came from one rewinder who said that it would be difficult on a small diameter spindle to use the heavier duty wire necessary to change.

Not sure it was a very logical comment, I would expect the requirement would be for more turns of a smaller dia wire.

[GEOFFREY]

Oops!! That could be my misinterpretation. Perhaps he meant not enough room to get the turns in. Anyway, they said it would be impossible - I guess they were just not interested. G.

[johnsattuk]

Perhaps he meant not enough room to get the turns in. Anyway, they said it would be impossible - I guess they were just not interested. G.

I think you guess correctly, getting the turns in is not generally a problem, once you know the turns you have to decide on the wire dia that will fill the slots as much as possible, bigger is better but it depends on the practicalities of getting them in. It may be that the number of turns required reduces the dia of the wire enough to limit the current, and thus the power of the motor.

What is the current rating of the existing motors, may be cheaper to get a VFD with enough amps to drive them, you would be able to program it for the volts.

Be interesting to see Jonathan's winding solution.

[GEOFFREY]

Thanks for the reply, but it is not possible to find a suitable replacement VFD. The problem as I understand it is that the spindle (900w max) is a 2 pole 3ph motor with a speed range of 15-60krevs at 15-60volts. I do not need that speed, so would be happy with 24krevs at 230volts and use an off the shelf inverter. I have been advised that whilst I may be able to set the voltage down that low with a 400hz inverter, these inverters are PWM and would still be applying a higher voltage for a short period to achieve the lower working voltage, but that the spindle low voltage windings will not be insulated sufficiently to cope with that. I hope that makes some sense. I certainly had the impression that the "impossible" comment was because there would not be enough space for the revised windings, or indeed that they were not really interested. The spindle body diameter is 62mm, but none of the rewinders I spoke to have seen the spindle, let alone examine it. G.

[Jonathan]

Rewinding a motor will only increase its torque rating if you manage to fit more copper in the stator slots than the original. Changing the number of turns in series/parallel (etc) primarily changes the voltage rating - it is the *total* current through the slot that matter when calculating the torque output. The total current you can put through the slot depends on how much copper you can fit - too much current or too little copper = more heat.

If you just copied the existing winding, but increased the number of turns by the ratio of the new to old voltage rating, then it would be OK. We can go into a lot more detail if you want to, but it's hard to say how much there is to gain from this without actually seeing the motor inside.

Thanks for the reply, but it is not possible to find a suitable replacement VFD. The problem as I understand it is that the spindle (900w max) is a 2 pole 3ph motor with a speed range of 15-60krevs at 15-60volts.

That is well within the rating of the VFD I have designed/made.