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  1. #21
    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.

  2. #22
    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.

    Quote Originally Posted by GEOFFREY View Post
    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.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

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