Max. speed range, 2 or 4 pole

[Barry1961]

I have an application for a machine/conveyor that needs a large speed range. The customer would like a 16:1 range but can live with less. I have been able to do 10:1 ranges without feedback using 4 pole motors.

Would like:
Top speed, 35 in-sec with 1% speed variation allowed
Low speed, 2 in-sec with 7% speed variation allowed
Horsepower, .5 hp max.
Drive Pulley, 1.43" PD (not actual but good for calculation)
The motor is driving multiple mechanisms.
Torque, 60 in-lb max.

I would like to use a sensorless vector and stay away from feedback. At this time I am planning on using a 1 hp, 4 pole motor. In past experience the speed control gets mushy on the low end but since I can have a 7% variation on low end I was hoping to get down to 5 hz.

Is there any advantage to using a 2 pole motor as far as speed range is concerned? I know the gearbox will cost more for a 3600 rpm input. My gut tells me that a 2 pole will not do as well at low hertz where it really counts.

Any guesses on what speed range I can get with the allowed variation in speed?

Barry1961

 

[Skogsgurra]

I think that you should stay with 4-pole. It is much more standard than 2-pole. And the gearbox is cheaper too.

A modern sensorless vector drive should be able to go down to 1 or 2 Hz without getting too "mushy". Old scalar drives used to have that problem.

 

[DickDV]

And consider taking the 4 pole motor to 100hz (3000rpm) for conveyor top speed. That would calculate to about 6 hz on the bottom end.

Either way a good sensorless vector drive should be able to provide good speed accuracy and stability at 1 hz and higher.

 

[mc5w]

However, taking the motor above 60 Hertz requires a gearbox that is rated for the excess speed. Most gearmotor manufacturers warn against connecting a motor for 230 volts and hooking it up to a 460 volt drive so as to run constant torque up to 120 Hertz.

At 5 Hertz you should be able to use either tachometer or shaft position encoder feedback. I would seriously consider using that.

Also, for your speed range you need a totally enclosed nonventilated motor or a blower cooling kit. The former is cheaper.