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Control multiple motors by one Variable Frequency Drive

1. You can even run more than 2 motors on a single variable frequency drive; it is absolutely OK, I am using it for quite a long time and the VFD is just working very fine.
2. In one application I had used 8 Motors (screw conveyors) on a single VFD (Gozuk make) we had no problem in that configuration.
3. In another application I used ABB 22KW VFD, to run 2x11 KW induction motors this was used on large EOT cranes and the motors were used for the long travel of the EOT cranes.

Running multiple motors on a single variable frequency drive, certain conditions, considerations and safety must be met, here are few guidelines you'd better follow:
  • VFD should be at least 20% more power of the two motor power clubbed together. So go for next higher rating available for VFD.
  • Set VFD to V/F mode, no vector at all (see V/F mode VS vector mode).
  • Set correct current rating
  • Don't perform Auto tuning
  • At the VFD output put right OLR for each motor
  • NC of OLR should be wired to VFDs enable terminal, so that any of the motor goes to fault VFD should be disabled.
  • NOs of OLR and VFDs can be used for fault display
But please keep in mind that you can only set the variable frequency drive to V/F mode control if you control multiple motors by a single VFD, never set VFD to any Vector control, even at open loop with Vector control, otherwise the VFD will be burned.

So the bottom line, go ahead with your project. It is absolutely fine to run more than 1 motor on single VFD till the KW is matched and the parameters are set correctly. This is the key of any VFD application.
I have worked on applications dating back to the late 70's running 40-60 motors on the same variable frequency drive. Additional issues to consider are:
1. You can only control multiple motor on one VFD by setting it in V/Hz mode. Open or closed loop vector modes won't work in this type of configuration. I have seen one application using two motors on an open loop vector VFD running in torque mode but if you get it working and ever have to replace one of the motors it may not continue to work.
2. Make sure that you use the proper line reactors if you are running the motor leads a long distance. You can mitigate the need for this somewhat by changing the carrier frequency of the variable frequency drive, but I recommend going with the line reactors.
- - - -> by: Mike
You can do if setting VFD correctly, however personally I don't like to do this as unknown little fingers bridge out O/L units and keep quiet etc so one of the motors burn out. then cause unnecessary downtime. I have come across systems with 3 or more motors on one drive,but also as stated depends on the application.
- - - -> by: Keith
you have to share the same load on each motors in the same time. More ever it depends of the type of Drives ... DTC control or not , with encoder or open loop etc .... and consider about rating of each motor and install two separate Motor protections.
- - - -> by: Sam Chang
Yes, its possible. We are regular user of this type implementation with sensorless vector control /DTC mode. For such application we prefer to go for ACS800 Demag series variable frequency drive which is manufactured by ABB - Finland for Demag Cranes .To get better result go for identification run of motor in sensorless vector control. Apart from various other experts input take care as per following.

1. All Motor required of identical rating
2. Provide Thermal overload protection in series with each Motor
3. Depends on length of cable between Motor & VFD provide output choke as per VFD manufacturer recommendation.

Recently we have implemented 6 project in crane application with above said consideration.
- - - -> by: Sandeep
yes you can run multiple motors on one vfd but total KW of motors should be equal or less then rating of vfd
- - - -> by: Patel
When using an inverter duty motor with a VFD, do one or both bearings on the motor have to be insulated?
- - - -> by: Eric
For running multiple motors using single vfd, is it not necessary that all motors should of same rated rpms?
Otherwise if rated rpm of one motor are more than other motor then at rated frequency of suppose 50 Hz both motors will be running at their rated rpms which are not equal ?

I am talking about an application where all the motors being controlled by vfd are running a common conveyor at a constant speed.
- - - -> by: Muhammad Khalil Yousaf
We are currently getting 4 50 hp motors set up to run a dust collector. We are using gates at each machine to open when the machine is turned on and the motors ramp up as needed to maintain 4000 feet per minute in the trunk.
I am now being told that they can only run the motors in steps. 52kz 54hz
56hz 58hz and 60hz.

I was expecting it to run between 30hz and 60 hz. Are my expectations not feasible? Can anyone tell me if its possible
- - - -> by: gino
How would you wire multiple motors to a single VFD?, would it be same as for one unit?

I am looking at operating 4x25 kW motors simultaneously and under identical conditions using a single VFD.

Also, is there a particular VFD manufacturer or a particular specification for the VFD to operate efficiently other than what already has been highlighted in this thread?

Thanks in advance,
- - - -> by: Dan

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