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Synchronous electric motors

Synchronous electric motors If you need an electric motor that won't be at risk of burning out if it stalls, or that offers much higher efficiency than a standard induction motor, or runs smoothly and quietly, then a synchronous motor may be exactly what you're after.

A synchronous motor is an AC motor in which, in a steady state, the rotation of the shaft is synchronised with the frequency of the supply current, such that the rotation speed is exactly equal to an integral number of AC cycles. Electromagnets on the stator create a magnetic field which rotates in time with the oscillations of the line current, and the rotor turns in step with this field.

Synchronous motors such as those within the Rotek range offered by OEM Automatic are easy to drive and can be readily used with standard inverters. Further, if you have an application where motor stall is a real possibility, then the synchronous motor is ideal. Synchronous motors can be stalled for long periods without risk of burning out.

Further, these motors can provide big benefits beyond those afforded by the synchronous nature of the motor, delivering real advantages in a raft of applications. They are more efficient than standard induction motors, so a smaller motor could be considered for a given application. Where a good quality single phase induction motor might be just 45% efficient, the equivalent Rotek synchronous motor boasts 60% efficiency, and while the same induction motor in a three-phase version will be 70% efficient at best, the Rotek equivalent is 90% efficient.

Additional benefits include very good speed holding and smooth, stable running, regardless of changes in load, because the motor locks onto the frequency it is being driven at. This makes the motors ideal for applications where precise speed holding is required. They also offer good holding torque - in some cases eliminating the need for a holding brake. Other advantages include light weight and compact size for a given output, with a low heat dissipation which does not vary with changing load.

The Rotek family of motors from OEM Automatic provides a compact range with thousands of options. With over 15 years experience, Rotek is one of the world's leading exponents of synchronous motors from 10-100W, and offers a comprehensive portfolio of products that embraces motors, gears (spur, planetary and worm), shafts, encoders and other accessories. With literally thousands of combinations available, solutions can be precisely tailored to the needs of the specific application.

Forming the foundation of Rotek's unique modular system is the Robase motor - a classical synchronous motor equipped with prominent stator teeth and ferrite magnets, delivering excellent self-holding torque and impressive service life. With a motor diameter of 65mm, the Robase motor offers speeds up to 1000rpm at 50Hz in 6-pole versions or 1500rpm at 50Hz in 4-pole versions. Output power is from 8-30W.

For maximum performance coupled to low power consumption, single-phase Rosync motors are up to 75% efficient and three-phase motors up to 90% efficient. This is particularly important where long running periods are required, for instance in conveyor belts. In comparison to conventional single phase synchronous motors, they offer up to 40% more output power.

With a motor diameter of just 65mm, the high performance-to-size ratio makes the Rosync ideal for use where space is limited. These 6-pole motors offer speeds up to 1500rpm at 50Hz and powers from 20-36W (S3 to 50W) single phase, or 50-85W three-phase. Further benefits include a long life expectancy, short starting and stopping times, and a maintenance-free design.

When smooth running is the prime concern, the Roslyde motors are the ideal solution, with their low-vibration, low-noise running down to Rotek's 'SmoothDrive' technology. This makes the motors ideal for laboratory and domestic applications such as wood-burning stoves and rotary heat exchangers. While not having the self-holding torque of other motors in the Rotek range, Roslyde motors are virtually silent in operation, and so are ideal for applications where any noise would be regarded as intrusive. The 6-pole motors offer speeds up to 1500rpm at 50Hz, with output powers from 11-20W single-phase, 20-40W three-phase.

Complementing these motors is a full range of gears. Flexible and durable spur gears are available with ratios from 5:1 to 1333:1 and torques from 6-13Nm. The hardened steel gears, high quality lubrication and durable sintered bronze bearings given them a long service life. Worm gear transmissions are available wherever a second shaft or a 90° deflection of forces is needed. The polished worm and bronze wheel ensure smooth running, and if particularly quiet operation is required a durable fabric-based laminate can be used. Gear ratios from 2.5:1 to 100:1 are available, with torques from 5-12Nm.

Where space is a prime concern, three flat-gear series meet a variety of requirements, with output torques of 10Nm, 20Nm and 27Nm. The smallest gear is fully fitted with ball bearings and is suitable for the most demanding applications, while the medium gear is a durable, low-cost design for higher volume demands. The strongest gear has a hollow shaft with ball bearings and can be fitted with an optional release mechanism.

Where high torques are needed within the most confined spaces, planetary gears offer torques from 3-50Nm for motors up to 100W. For short periods they can be subjected to up to 50% overload. Their durability, lack of maintenance and range of variants makes them ideal for the most demanding applications. Combined with Roslyde motors, the low-noise variant offers a particularly smooth running drive unit.

OEM Automatic has found numerous applications where the specific features of these synchronous motors have proved particularly beneficial. From joystick controlled CCTV cameras to industrial access gates, the motors have successfully eliminated problems of burn out should the motors stall. The fixed speed running has also proved a problem solver, in applications from fixed speed conveyors with varying loads to dosing and to a blood separation system which separates blood from plasma.

OEM Automatic UK has over 25 years experience in supplying leading products to industry, with a product range that is one of the widest and deepest on the market. The company operates in four key business areas: motors; panel products; machine/safety; and pressure/flow products. OEM Automatic can also help to select the best products for each application, and reduce the number of suppliers, so lowering the total cost of purchasing. Through its market presence, customer focus and high level of service, OEM Automatic adds real value to the supply chain.
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