View Full Version : AC servo motor to replace a 3 phase induction motor on a mill spindle.

23-04-2014, 11:21 AM
Hi all,
I am trying to replace the spindle motor on my mill (a 3 phase motor running from an inverter) with an AC servo motor.
Now, the original motor is a 3 phase (delta 240V) / 0.37KW / 4 poles / 1400RPM
The servo I have is: AC / 0.75KW / 3000RPM

The servo is physically a lot smaller but the power rating is a lot more... That get me a bit confused...
How is it possible to get twice more power in about a 1/3 of the size ?

Is this servo big enough to replace the original motor or would it struggle ?


23-04-2014, 01:18 PM
"How is it possible to get twice more power in about a 1/3 of the size?"

By being much more expensive :-)

Think the main factor is that in the brushless permanent magnet design usually used on servo motors the coils end up on the outside right up against the motor casing, so they can radiate heat well, so you can get a higher power rating in a smaller package.

So yes, you'll likely have enough power. Note though that the rated power is usually given at max RPM (3000 for the servo, 1400 for the current one) so the power ratings of the two motors at 1500 rpm might be more equal than the raw numbers suggest. Of course you may be able to alter the gearing to take max advantage of the servo. There should be manaufacturer data for it in the form of a torque vs rpm curve from which you could work out the power at any given RPM.

23-04-2014, 03:14 PM
Thanks for the reply!

I'll give it a go and see...