I currently am running some different motors, some complete with Reduction Drives. Some three phase, and some single. I am wondering what my options are to vary the output speed of these motors units.(Both the three & single phase) I have searched through some old threads in this forum, and notice VFD is commonly reffered to. I looked into what it was, and learnt it varies the frequency, hence the speed. What other options, both mechanically and electrically, do i have, and should explore into?
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Varying Speed of a Motor
- Thread starter Marktal
- Start date
Hello Marktal
I have some brief information on variable speed on my web site at This lists a few of the options that you have.
If you look at directly changing the speed of the induction motors electrically, you do this by varying the frequency and voltage applied to them.
This only works for three phase motors, basically you have to ignore the single phase motors.
The disadvantage of VFD technology, is that at reduced speeds, the maximum torque is limited to the rated torque at full speed. In otherwords, the effective power capacity of the motor reduces with speed. You must ensure that there is sufficient torque at the lower speeds. Mechanical speed controllers provide rated power at reduced speed and thereby an increased torque at reduced speed.
The advantage of the VFD, is that the speed is continu0ously variable and can be automatically controlled by a feedback loop.
For high torque at low speed, look at DC machines rather than AC.
Best regards,
Mark Empson
I have some brief information on variable speed on my web site at This lists a few of the options that you have.
If you look at directly changing the speed of the induction motors electrically, you do this by varying the frequency and voltage applied to them.
This only works for three phase motors, basically you have to ignore the single phase motors.
The disadvantage of VFD technology, is that at reduced speeds, the maximum torque is limited to the rated torque at full speed. In otherwords, the effective power capacity of the motor reduces with speed. You must ensure that there is sufficient torque at the lower speeds. Mechanical speed controllers provide rated power at reduced speed and thereby an increased torque at reduced speed.
The advantage of the VFD, is that the speed is continu0ously variable and can be automatically controlled by a feedback loop.
For high torque at low speed, look at DC machines rather than AC.
Best regards,
Mark Empson
There is also a traction ring drive. With this type there is a traction ring at a slight angel driven by the motor and a disc on the input of gearbox. The motor and traction ring are then cranked up or down to cause the traction ring to contact the disc closer to or further from center.
I think the only people who make these are Stober. About the only place where they are still used is in the agriculture industry for conveyor drives. This is because the design is so simple that it can be repaired by unskilled workers.
In general the VFD’s are the most popular.
Barry1961
I think the only people who make these are Stober. About the only place where they are still used is in the agriculture industry for conveyor drives. This is because the design is so simple that it can be repaired by unskilled workers.
In general the VFD’s are the most popular.
Barry1961
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