PCS Or PF Softstarters Used In Multi-Motor Applications
Question:
Can I use a single PCS or PF softstarter to control and start more than one motor at the same time or to start multiple motors simultaneously? What installation procedures, recommendations and programming parameters should be changed for this application?
Answer:
Yes, a single PCS & PF soft starter can be used in this application to start multiple motors at the same time. When this is done, the soft starter must be sized for the combined full load currents of the motors. Generally, when using Soft Starters in this application the best results are obtained when the motor shafts are physically coupled so that the load being started is shared by all motors. This can be done through belts, a gearbox, or other coupling methods.
When multiple motors are not physically coupled, the acceleration rates of each motor can differ due to differences in the load seen by each motor. In some cases the back EMF that the soft starter is reading can become distorted if the motor loads are significantly different. In this case several lightly loaded motors may "trick" the soft starter that it is up to speed and "tells" the soft starter to go to full voltage.
If this happens there is a remedy that can be applied by using parameters in the PF soft starter (but not on the PCS). When the PF parameters are enabled the soft starter forces the voltage ramp to continue for the entire programmed time. If you need assistance with programming, contact Technical Support for assistance in accessing these parameters. See the recommended procedure below for selecting and setting the soft starter for use with multiple motors:
- Size the Soft Starter per the combined motor sizes (add all of the motor full load currents.)
- Select overload relays for individual motors. Each motor will require its own overload protection under this type of installation per the NEC code.
- Select Soft Start mode for the Starting Mode parameter.
- Turn overload protection off on the soft starter as they are individually protected per the NEC code.
- Set Motor soft starter FLC (Full Load Current) parameter to the sum of all the motors' full load currents.
For additional information please contact your nearest authorized distributor, sales representative, or call our customer service or technical support lines.
