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Frequently Asked Questions

Q. Is a drive required to operate VFsync (PMAC) motors?

A. Yes, all commercially available permanent magnet motors require a variable frequency drive to operate.

Q. Can I use any VFD to control the PMAC motor?

A. The drive must be specifically capable of operating PM (Permanent Magnet) motors.  Theses PM drives use motor data and current measurement to calculate rotor position.

Q. Can the magnets in the PMAC motor degrade or reduce performance over the life of the motor?

A. The magnets used in the VFsync motor do not degrade due to use of the motor in normal operating conditions.  It is possible that extreme over temperature conditions can demagnetize the magnets.

Q. Are permanent magnets subject to demagnetization?

A. High current or high operating temperatures can cause magnets to lose their magnetic properties.  Many VFD drives (like those that Bison offers) are equipped with an over-current protection circuit.

Q. What are some of the major differences in performance between AC Induction and PMAC?

A1. PMAC motors run more efficient than induction motors and consume less energy as a result. The main reason is that the rotors are already magnetized using magnets whereas rotors inside induction motors develop magnetic poles due to induced currents from the stator field. The energy needed to magnetize the rotor in an induction motor is not required in the PMAC motor.

A2. Lower operating temperatures can be obtained in PMAC motors as they are more efficient.  Lower temperatures extend operating life of the electrical insulation system and the lubricants used within the bearings.

A3. When PMAC motors are compared to Induction motors of the same power level, the PMAC motors are smaller and as a result have higher power density.  Since the rotor is already magnetized the stator size requirement is reduced which leads to lower stator core losses and higher efficiency.

A4. Induction motor operating speed is always slower than the rotating field generated by the frequency of the alternating current. Due to a variety of factors, the variance between the two rotating velocities may contribute to unplanned performance issues in a driven machine. PMAC motors have no slip. The rotating field velocity is equivalent to the rotor velocity, providing the machine builder better control and predicted performance.

Q. What are the primary benefits of PMAC motor versus AC Induction?

A. Permanent magnet AC motors are inherently more efficient due to elimination of rotor conductor losses, lower resistance winding and “flatter” efficiency curve.  Due to their synchronous operation, PMAC motors offer more precise speed control. 

PMAC motors provide higher power density due to the higher magnetic flux as compared with induction motors.  Since the magnetic fields generated by rare-earth magnets are up to four times as powerful as other commonly used permanent magnets, PMAC motors can deliver the same torque as AC induction motors with a smaller, lighter motor footprint.  


Q. What is Power Density?

A. This refers to the ratio of the power output to the physical size of the motor.  It’s a benefit to those application that are limited in space.


Q. Are VFsync motors suitable for both variable and constant torque applications?

A. Yes, the VFsync can be applied to either application. Parameters within the VFD can be set to deliver specific current levels and control torque output.

Constant Torque Application (require the same pushing or turning force (torque) at all speed in the operation range of the machine) Conveyors, Hoists, Positive displacement pumps.

Variable Torque Application (easy to start and requires more torque as the motor speed is increased) Centrifugal pump, Centrifugal fan, Low viscosity mixers.

Q. What is the watt/HP rating range of for VFsync motors?

A. Current standard product offering 187W/0.25HP – 1.1kW/1.50HP

Q. What is the ingress protection of the motor?

A. The motor is IP54 rated

Q. Can I operate PMAC motors using 115V/60Hz?

A. Bison offers two motor operating voltages: 0.25HP – 1.5HP operate on 230V and 0.75HP – 1.5HP operate on 460V

Bison’s VFD drives can be ordered with four available input voltages, 115V or 230V single phase, and 230V or 460V three phase.

Q. Are VFsync motors a stocked product, or built to order?

A. VFsync motors are built to order from component inventory at our manufacturing facility in St. Charles, Illinois.  Two-week lead-time for low quantity orders is typical.

Q. What are the efficiency gains in % over induction motor of same HP?

A. The efficiency gain is between 15%-25% when compare to an induction motor with the same HP.

Q. What is maximum speed that VFsync motors can operate?

A. VFsync motors are designed for continuous duty at 1800 RPM.  The motors can be operated at speeds up to 2500 RPM in intermittent applications. Consult Bison Engineering for guidance regarding higher speeds.

Q. Do PMAC motors offer energy savings in Constant Torque Loads?

A. Yes, when you compare AC IM and PMAC motors, PM motors consume less power to produce same amount of torque in either type of loads. Thanks to its very low rotor losses as there is no current induction into the rotor bars, which makes PMAC motors more efficient and results in energy savings.  


Q. How do PMAC motors compare to Induction motors when used on VFD’s at low speed?

A. The recommended continuous torque-speed ratio for a typical induction motor with a VFD is 2.5:1. For example, if the motor is rated at 1725 rpm speed, the lowest speed one can get reliable speed control is 690 rpm.

As PMAC motors do not have slip, they can be operated up to a 10:1 speed ratio at the constant nameplate torque. That means the motor can be operated at full-load torque from 1800 rpm to 180 rpm, synchronously with the VFD.  

In closed loop applications, one can achieve zero speed with full load torques in PMAC motors.

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