External Rotor Motors utilize multi-pole NeFeB magnets.

Press Release Summary:

Measuring 63 x 52 mm, VDC 3-49.15 Series is available in 2 versions with nominal voltage of 48 and 24 Vdc and operating voltage range of 18-55 or 18-30 V. Units feature output power of 105 and 63 W at 2.9 and 3.5 A current consumption, respectively. With nominal speed of 4,000 rpm, nominal torque reaches 250 mNm or 150 mNm, while max torque controlled by I2t function can be twice as high. Maintenance-free motors include solid flange with 3 tapped holes for direct mounting.

Original Press Release:

New Generation of External Rotor Motors from ebm-papst

Many applications require small yet reliable drive units. Unfortunately, while compact internal rotor motors have a small diameter, they derive their performance out of an increased length or high operating speeds. Therefore they frequently require a multi-stage reduction gear unit for many drive tasks which makes the complete drive unit rather large. However, compact overall dimensions and high dynamics can now be found in the new generation of external rotor motors from ebm-papst. With high constant torque over a wide speed range, the use of gears is avoidable or the number of gear stages can be reduced. This way the VDC 3-49.15 is more compact and is easier to integrate into the application and thanks to cost-effective production methods, the price of the "power package" is supremely competitive.

Modern electronics focus on distributed and decentralized intelligence, a trend that applies increasingly to smaller drive units where a compact drive is required. A power output of around 100 Watt is sufficient for many areas of application where dynamic control behaviour and a highly adaptable speed range are required. In order to fulfil these requirements ebm-papst, the specialist for small external rotor motors from St. Georgen in the Black Forest, has developed the new VDC 3-49.15 motor generation. Innovative design, and the use of components and production methods based on new technologies enable the manufacturing of these highly competitive, high performance motors to be the top of the class.

Setting New Standards

For the Black Forest specialist, external rotor motors have long been a state-of-the-art feature of small fans and drives. This extensive experience has been used for the continued development and optimisation of such external rotor motors. Contrary to "fan motors", a drive motor which is suitable for universal use requires a completely different motor configuration. Achieving high torque over a wide speed range or high overload capability combined with a high starting torque are important factors. Additionally, a high efficiency, reliable control at low speeds, an electrical holding torque at speed "0" as well as quiet operation and easy integration in the application are also required. To solve these manifold requirements, the ebmpapst engineers based their development on the principle of a multi-pole external rotor motor (Fig. 1).

The introduction of a multi-pole magnet in the rotor housing and a corresponding number of poles at the stator winding simply mean a higher coverage of magnet and stator pole at all times and thus a multiple torque (Fig. 2a,b) - somehow similar to a higher number of cylinders in a combustion engine. With this the motor is even able to provide substantial torque already at lowest controlled speeds, so that the number of stages of the gearbox can frequently be reduced. Despite the many poles, the stator poles of the external rotor motor have the slots open towards the outside which makes the winding process much easier than the winding of comparable stators of internal rotor motors. The use of modern NeFeB magnets enable outstanding performance values to be achieved. Nevertheless, the cogging torque is less than 1% of the nominal torque.
With the cup-shaped iron rotor housing the magnets are securely supported against the centrifugal forces so that the motor remains completely stable at high speeds. Integrated electronics that operate with field-oriented control (FOC), supply the stator winding in the star winding configuration with required voltage for smooth sinus commutation (Fig. 3) which ensures that the winding is optimally used and accoustic noise is reduced further. Even the operating efficiency increases with this type of commutation. Mounted on a 6-layer HDI PCB, the powerful electronics improve the efficiency of the motor. Variable current limitation per analogue set value voltage as well as varying additional inputs and outputs enable extensive drive functionality. Using different types of software, different motor characteristics can be parameterised from the R&D experts to suit the application. Further options, e.g. position controller, single turn absolute encoder or an RS-485 interface can be provided on request for customized projects. Two analogue and four digital inputs as well as three digital outputs can now be used for integration in the application. An optional BUS connection in preparation will also become available for changing parameters during operation or for receiving current motor data for further processing. All components of the SMD-assembled PCB are AOl tested. Importantly, both PCB and motor fulfil the basic requirements relating to EMC and creepage distances that are necessary e.g. in medical applications. The specially developed, fully sealed cable connection is attached as a separate module to the motor and enables further flexibility in the designing of adapted interfaces and functionality (Fig. 4a,b).

High Performance Data

The performance data of the two motor versions are outstanding: Nominal voltage 48 respectively 24 V DC, and operating voltage ranges from 18 to 55 V or 18 to 30 V. With a nominal speed of 4000 rpm, the nominal torque reaches 250 mNm or respectively 150 mNm while the maximum torque controlled by an I2t-function can be twice as high. The drives have a 105 and 63 watt nominal output power at 2.9 A (48 V) and 3.5 A (24 V) current consumption. With dimensions of only 63 x 52 mm (diameter x length) the motors are extremely compact. Therefore the VDC 3-49.15 achieves high ratings with regard to nominal power per construction volume and mass. A bearing system that is purposely designed to meet the high requirements has a service life of up to 40.000 h even under the most arduous operating conditions. The motors can operate over the entire speed range from 0 to 4000 rpm and are maintenance-free. In addition The powerful motor version with NeFeB magnets, reaches its maximum operating efficiency of over 80% within a wide torque range with virtually optimum operating efficiency and thus has high power in reserve.

The solid flange of the motor with three tapped holes is designed for direct mounting and is suitable for the adaptation of different gears. Spur and planetary gears are suited exactly to the motor characteristics, so that optimum combinations can be realized, e.g. to produce quiet operation or maximum torque.

Universal Use

The VDC 3-49.15 compact drives are suitable for many fields of applications. In the medical or laboratory technology they power sensitive metering pumps with a wide speed (flow) adjusting range e.g. peristaltic pumps in dialysis machines. In other applications they can also be used for the force- and speed-controlled operation for passive movement rehabilitation and training devices. In packaging technology and the textile industry the adjustable torque limitation and accurate closed loop control allow e.g. optimum adaptation of the winder drives to the processes and materials used. Thanks also to its 4-Q controller, the high overload capability of 2 x nominal torque MN and the digital fault output, the drive is also optimally equipped for electronic gears as used in letter sorting systems or other demanding applications.

The new VDC 3-49.15 multi-pole external rotor motors are both powerful and compact. The wide speed range and corresponding torque enhance the dynamic values of the motors. Based on these performance features the VDC-3-49.15 can be used in applications where only internal rotor motors could have previously been considered. All motor functions are controlled via integrated electronics enabling the relevant operating data and error messages to be transmitted to the customer interface if required. A special, application-specific motor configuration is possible by simple programming or parameterization of the control electronics. This saves overall costs for the system designer in development, production and storage.

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