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VFD with shared motors on a roll handling belt application
5

VFD with shared motors on a roll handling belt application

VFD with shared motors on a roll handling belt application

(OP)
We have a new material handling project that calls for the use of two motors on a reversing, chain-driven conveyor belt. The plan calls for two drive motors, one on each end (drive roller) of the conveyor. It also calls for one VFD to supply the power to both motors. I am concerned that the two motors will not be synchronized and this may cause issues with power if there are differences in the gearmotor speeds, gearing in the gearbox or slipping on the belts or if the motors try to work against each other creating artificial load. Is this a proper application for a standard duty VFD? What steps should be taken in this type of application to reduce the risks of problems associated with opposing motors with no feedback?

RE: VFD with shared motors on a roll handling belt application

No problem with induction motors.
The torque in an induction motor is developed by the very low frequency induced current in the rotor.
A 1760 rated motor will run close to 1800 RPM when unloaded.
As the load increases, the rotor slip and the frequency of the induced rotor current current increase and the motor slows slightly, until at full load it will have slowed to 1760 RPM.
Similar motors, energized with the same frequency will share a load very well with no further though or action on your part.
Even if the drive chain at one end is slacker than at the other end, so that when the motors reverse, one motor drives immediately and the other motor must first "pull slack", the motors will work it out within a few revolutions.
Synchronous motors definitely have problems such as you anticipate, but you will not have synchronous motors.
"Don't worry. Be happy."

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: VFD with shared motors on a roll handling belt application

2
Twin drive motors (or multiple drive motors like conveyors) are all from the same OEM with almost identical operating characteristics and have been operating successfully (with or without VFD's) without any issues for decades. Just don't mix motors from two different OEM's.

Muthu
www.edison.co.in

RE: VFD with shared motors on a roll handling belt application

Yes, done all the time when motors are mechanically coupled. As Muthu says though, the motors should be the same because you want the slip to be the same. If the slip is different they will not share evenly. So if you ever have to replace one motor, replace them both with identical motors.

But they will never really be “working against each other”, the worst case is one working slightly harder than the other, like 52 vs 48 percent.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: VFD with shared motors on a roll handling belt application

Don't match a 1760 RPM moor with a 1740 RPM motor.or as jraef mentioned, the 1760 motor will hog the load.
When the 1760 motor is fully loaded the 1740 motor will be at about 67% load. That may or may not be acceptable.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: VFD with shared motors on a roll handling belt application

(OP)
Thank you all for your input.

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