Huanyang VFD - RPM is not reading correctly

Spindle/VFD (Aftermarket)
9

Hey Tim,

  1. you can measure the currents the spindle produces if you turn it manually. Every induction motor is an induction generator. You can connect a multimeter which is set to 200 V DC between two of the three phase pins and turn the spindle manually. If you get one positive and one negative pulse value per turn, it has two poles. With four poles, you would get double the number of positive and negative pulses per turn. Here you see a diagram of a three-phase induction motor, at left with two magnetic poles and at right with four magnetic poles:

  1. You can deduce it from rated rpm and frequency. If your seller tells you it is rated 24,000 rpm at 400 Hz, you can calculate the number of magnetic poles back:

    The rotational speed of a spindle is calculated this way:

    SPINDLE_RPM = $VFD_FREQ × 2 × 60 / $SPINDLE_NUMBER_OF_POLES

    e.g. 400 Hertz × 2 × 60 seconds / 2 poles = 24,000 rpm
    or:   400 Hertz × 2 × 60 seconds / 4 poles = 12,000 rpm

    This means with a spindle with two magnetic poles a VFD will make the spindle run with 24,000 RPM spindle speed at 400 Hz. If it was a spindle with four magnetic poles, at 400 Hz, it would run at 12,000 Hz according to the formula. To bring this spindle to 24,000 rpm, you would need 800 Hz.

So if you know how fast a spindle runs at a specific frequency (e.g. 24,000 rpm at 400 Hz), you do:

$SPINDLE_NUMBER_OF_POLES = $VFD_FREQ × 2 × 60 / SPINDLE_RPM
400*2*60/24000 = 2 poles

  1. You can deduce it from price. Spindles with four poles are more expensive, e.g.
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