motor questions

[Ken S]

Using 50 and 60 motors in an identical tool, like the Tormek T3/4, would there be a difference in the heat given off by the motors due to the Hertz or voltage difference?

Would there be a difference in the amount of surge starting current? (This should be of interest to Bobi.)

[Jan]

Ken, it is a tricky question! 

For time varying current/voltage the average power is P_avg = V_rms * I_rms
where V_rms and I_rms are root mean square values of voltage and current. The formula shows, that the average power does not depend on current/voltage frequency. But the formulae is true only for purely resistive load. Root mean square voltage and current will produce the same heating effect as direct current in a given purely resistive load.

Tormek motors are reactive loads for which the voltage and current are out of phase. This is described by the power factor, which even more changes with motor load.

Generally one can say that the use of lower frequency provides the advantage of lower impedance losses, which are proportional to frequency. 

Jan

[Ken S]

Jan,

Excellent answer, but above my technical knowledge. From your last sentence, I would guess that the 50 Hz motors are somewhat more efficient than the 60 Hz motors.. Would a 10 Hz difference be enough to be noticeable with heat produced by the motor or the starting current required?

Ken

[Jan]

Ken, I deliberately avoided a clear answer because the path from laws of physics to a real description of the behaviour of asynchronous motor is not easy. 

Provided that the impedance loses in the motor winding are dominant contribution to the heat produced by the motor, then the 50 Hz motor should produce less heat than the 60 Hz motor of the same wattage.

The 10 Hz difference may cause that the 60 Hz motor will produce by 20% more heat than the 50 Hz motor (60/50). Such an increase of heat power is enough to be noticeable. On the other hand the RPM of the 60 Hz motor's are by 20% higher, which can ensure more intensive ventilator cooling and keep the temperature of the motor housing similar to the 50 Hz motor.

I dare not to compare the size of required starting currents.

Jan

P.S.: Mary Christmas to you and to everybody on the Tormek forum!

[Ken S]

Good post, Jan. It seems we just accept the electric power where we happen to live and grind on.

Merry Christmas.

Ken

[bobl]

Great post guys, but , I can only understand about 3 percent of the message. I am not an electrician.
Anything you can say in layman's terms would be appreciated. 

[Ken S]

As one electrical layman to another, my advice is to just plug in whatever motor matches your power and sharpen.

Ken

[KinndbergKennt]

How about this workaround, buying on Ebay :

AC Voltage Regulator £ 2 (ensures the torque)  +  Laser Tachometer £ 6  to ensure the wished amount of RPM.
A motor could be recycled from e.g. kitchen equipment or any other kind of machines.

I am going to rebuild an old Tormek st250 which originaly is delivered without a motor.
Want to keep it on a low budget, so I will find someone how can make the
- universal support
- horizontal base
- vertical base believe could be made with a shaft coupling where the inner diameter is 12 mm

Kent

https://www.flickr.com/photos/55973621@N06/sets/72157630041685187/

http://www.ebay.co.uk/sch/i.html?_from=R40&_sacat=0&_nkw=AC+Voltage+Regulator&_sop=15