are a Dahlander 2 speed motor and a vfd compatible? - Page 2
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  1. #21
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    Quote Originally Posted by Jraef View Post
    Don’t bother with all of that nonsense. Just permanently connect the motor in the highest speed and use the VFD to lower it.
    And lose half (or more) the motor power when pretending you have the low-speed motor by having low speed, same torque IF it does that well (IR losses are the same, so motor efficiency drops off too as you lower the speed/frequency - how efficient is an induction motor with DC power?).

    Connecting the low-speed winding and running it over frequency could be a better solution, you'd have more torque close to the design frequency, could run it up to the same RPM as the high-speed winding by supplying e.g. 120 Hz from the VFD. Depends whether you want torque for heavy cuts or not?

    Still, if you can use both windings, why not? I LIKE having that big lever for the 3 speeds, even with a VFD, it's part of the machine's design and a nice feature - and the VFD lets me do Useful Stuff, like near-constant surface speed by coupling a frequency control to the cross-slide, best of both worlds

    Dave H. (the other one)

  2. #22
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    "And lose half (or more) the motor power when pretending you have the low-speed motor..."

    Dahlander wound motors *are* half the hp at the half speed connections. Best approach for these is indeed
    a well-tuned sensorless vector VFD direct-wired to the high speed connnections.

    Don't like that? Build a rotary converter, use all your original kit.

  3. #23
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    Quote Originally Posted by jim rozen View Post
    "And lose half (or more) the motor power when pretending you have the low-speed motor..."

    Dahlander wound motors *are* half the hp at the half speed connections. Best approach for these is indeed
    a well-tuned sensorless vector VFD direct-wired to the high speed connnections.

    Don't like that? Build a rotary converter, use all your original kit.
    Badly designed and implemented Dahlander motors, perhaps - the BTH (trashcan-sized) motor in my Holbrook is 3HP (only 3 HP, it's a hideously expensive toolroom lathe, not a cheap production lathe) in all three speeds, pretty much the same current - think about it logically, at half speed two sets of pole windings each apply the same torque as the single winding (with fewer poles) at full speed, speed times torque is power so it's the same actual power delivered to the shaft. They could do it in England in the 30s/40s/50s, is this something that never made it across the Atlantic to the rebel colonies, or is it mystical lore lost in the ages?

    Plus using the high-speed, lower pole-count winding is already halving the torque compared to the low-speed winding (for the same current), so inherently less power at the same RPM - use the low-speed winding and run the VFD to higher frequencies, not rocket science, is it? The higher inductance of the low-speed winding will reduce the current at high Hz, but as you have more poles and more torque per amp what you lose on the swings you gain on the roundabout.

    Dave H. (the other one)

  4. #24
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    This is interesting. I guess this is a Dahlander motor? This motor flips all the windings to the same polarity, north for example, to create set of south fields in between the the windings. So the rotor sees twice as many fields as there are actual windings and the result is half speed. Hard for me to explain.

    YouTube

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