 Eddy Current Drives for Industrial Automation
- Integral Design
- Modular Design
- Drive-Brake Combinations
- Air-Cooled Drives
- Water-Cooled Drives
- High Speed Drives
- Totally Enclosed
- Eddy Current Brakes
- Geared Drives
- Electronics To Match
Eddy Current Adjustable Speed Drives
The Dynaspede series of Eddy Current drives comprises a family of AC adjustable speed drives, offered as a cost-effective solution to almost every industrial application requiring accurate, controllable, infinitely variable speed from an AC power source. These high torque, low inertia eddy current drives are mated with a variety of electronic feedback control options for precise control of machine speed or torque in single or multiple motor applications.
An eddy current drive is a combination of a constant speed AC induction motor coupled to an eddy current clutch. The function of an eddy current clutch is to transmit a controlled torque from the induction motor (prime mover) to the load (driven machine). The medium of torque transmission is a controlled magnetic field generated by a stationary field coil. A thyristor-based electronic controller is used to convert a relatively small amount of AC power into a DC power to excite the field coil.
The principle of operation is explained overleaf with reference to the following cut-away view of a standard, air-cooled eddy current drive.
Design Features
The following figures of merit may be compared for an objective study of eddy current drives of different brands.
Stationary Field
No slip-rings or brushes to wear. The coil is glass taped and epoxy moulded to prevent ingress of moisture or dust. All coils are made of high-grade polyester coated copper conductors. Insulation resistance guaranteed to be > 500 MW
Low Residual Torque
The active members of the coupling are made of specially alloyed, metallurgically controlled steel. The maximum residual torque is <10% of the rated torque, the typical value being <5%.
Low Slip Loss
Single most important figure of merit is the minimum slip loss needed to transmit the rated torque. Our Product Data figures reveal the Dynaspede advantage over competitive products.
 Operates Cooler
Lower losses in the coil and improved ventilation to enhance heat dissipation.
Branded Motors
Dynaspede drives come with the best known brands of induction motors.
Service Back-up
Extensive all-India service back-up and customer support.
Principle of Operation
The Drum-Fan assembly, forming the input member, is driven at a constant speed by a fixed speed prime mover which, in this case, is a flanged AC motor. The output member consists of a low inertia pole assembly connected to the output shaft of the drive. Thus there is no mechanical linkage between the driving and driven members to cause any mechanical wear and tear.
When the stationary field coil is excited by a low voltage (typically 45 volts DC, from the solid state electronic controller), a strong magnetic field is developed around the coil. The magnetic lines of force from the coil are guided to the pole pieces, through the working air gaps, into the drum assembly and back to the coil thus forming a closed magnetic circuit. The flux path through the working gaps between the pole and the drum is shown in the adjoining figure.
The flux lines are seen concentrated in the air gap near the pole faces resulting in a varying magnetic field around the periphery of the drum. Since the drum rotates in relation to the pole assembly, the surface of the drum experiences a time rate of change of magnetic field. Depending on the relative speed between these members, the induced cross currents (eddy currents), flow in the drum material.
The direction of flow of these induced currents is perpendicular to the magnetic flow lines as shown with conventional ¤ and Å signs. The reactive magnetic field caused by these cross currents is responsible for the torque transmission from the input to the output members, in these forms of torque transmitters.
 The extent of torque transmission depends both on the magnetic field strength and the relative speed (slip speed) between the drum and the pole. An increase in excitation, therefore, can correspondingly reduce the slip required to transmit a desired level of torque, thus providing an easy electrical means to control the drive speed.
Eddy Current Brakes work much the same way, except that one of the torque transmitting members is rigidly attached to the casing and is thus held stationary. Such a device therefore can exert a controlled braking torque, when the brake shaft is externally driven.
Clutch Brake Units have an eddy current brake in addition to a clutch. When used with solid-state Dual Channel controllers, eddy current transmissions can enforce close control of both acceleration and deceleration or other programmes of a rapidly changing nature of load.
 Speed Control is by a closed-loop speed feedback from an AC Tachogenerator of 48 poles, integrally mounted to the drive. Speed is maintained to the set value, despite load changes.
Torque Control is easy and straight forward. The intrinsic nature of an eddy current drive lends itself admirably to applications as constant torque or constant tension winding or unwinding.
Standard Electronic Controls
The modular design, add-on concept of the control units permit most control requirements from simple speed or toque control to complex systems to be effected with maximum economy.
The basic control unit is an Electronic Controller containing all necessary operator controls common for use with all ratings from 0.5 to 75 HP. Speed holding ability (against load) is better than 2%.
 Speed Controller Model AC40
General Purpose
Electronic Speed Controller with tacho feedback, common for drives up to and including 75 HP.
Standard features include Soft Start 0-30 sec, Preset Overload limit and Operator Controls
Specifications:
Input: 240 V. AC; ±15%, 1f
Output: 85 V DC(nom), 5A
Speed Holding: Better than 2%
ON/OFF: switch with Indicator
Set Speed: Potentiometer, single turn
Speed Indicator: Analogue
Ambient: 50°C
Construction: Wall /Desk mounting
Standard Options
AC40-7 with multi-turn potentiometer
AC40-16 with LCD display
AC40-8 with multi-turn pot and LCD display
AC40-10 features as in standard with JOG push button and JOG/RUN selector switch
AC40-11 multi-turn pot, JOG push button and JOG/RUN selector switch
AC40-12 with LCD display, JOG push button and JOG/RUN selector switch
AC40-13 with multi-turn Pot, JOG push button and JOG/RUN selector switch
AC40-3 with AUTO/MANUAL selector switch for accepting external speed reference voltage signal
AC40-15 with AUTO/MANUAL selector switch and multi-turn Potentiometer
Electrical Specifications |
Integral Design 
Transmissions
T.E. Drives
Modular Design
Fast Stopping 
Flanged Drive