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The following provides an overview of the nature and use of Powerform controllers for single phase motors.
WHAT PHASE CONTROLLERS DO
Powerform single phase fan speed controllers are called phase controllers. The controllers contain:
a. Fast acting solid state switches which vary the time for which mains voltage is applied to the motor being controlled.
b. An input system which is used to vary the output voltage of the controller.
c. Components which keep the controller environmentally friendly by suppressing unwanted high frequency currents and voltages to within the levels specified by environmental standards
APPLICATIONS
Powerform fan speed controllers provide stepless electronic speed variation of single phase motors in fan and pump applications
Conceptually, phase control is suitable for any load which has a torque characteristic which increases with speed, as does a fan load. Phase controllers are therefore used on axial fans, on centrifugal fans and blowers and on centrifugal pumps. Applications in which the fan or blower is mounted on the motor shaft will provide the most sensitive control, however controllers may also be used satisfactorily when fans are driven by light, flexible vee belts.
Powerform controllers are available:
a. To permit users to vary fan speed manually. Manual controllers with switches are also available.
b. To reduce air volume or excessive air noise when it is required that the user be unable to make alterations from the settings determined at installation.
c. As variable speed drives (VSD) for use in Building Management Systems where control of air flow rate is via a 0 - 10 volt or 4 - 20 milliamp interface.
d. For motor loads up to 10 amperes (2400VA)
Phase controllers are generally unsuitable for ceiling fans, which have high flux densities and loose stacking, often leading to unacceptable audible noise.
COMPLIANCE WITH STANDARDS
Powerform controllers are designed to comply with all Australian electrical and environmental standards. Installations must be in accordance with the instructions supplied with the controllers, and also with national standards, eg. AS3000. As appropriate, new designs are tested at external compliance laboratories.
In particular, when properly installed, Powerform controllers meet the requirements of Electromagnetic Compliance (EMC) standard AS/NZS1044:1995 which is identical to the European Standard IEC/CISPR14:1993. The controllers therefore carry the C-tick logo.
REQUIREMENTS OF MOTORS
For phase control, the single phase fan motors must be either split phase capacitor (PSC) induction motors or shaded pole motors. Clearly, an induction motor with a centrifugally switched start winding is unsuitable, as the short-term start winding would be energised continuously at low speeds.
It is preferable that fan motors intended for speed control be designed for that purpose. Desirable features include:
a. High resistance rotor
b. Means of cooling at low speed
c. Low flux density
d. Concentric shaft and rotor diameter
Suitable motors with matching fan loads can provide a range of speed variation from maximum speed to say 30% of maximum speed. For standard motors, the minimum speed should not be lower that say 80% of maximum speed (air flow rate reduced by approximately 35%). In any event, for standard motors, it is wise to ensure temperature limits are not exceeded at reduced speeds.
Street address: 33 Burraneer Ave, St Ives, Sydney, NSW 2075, Australia
Telephone: +61 2 9144 3973
Fax: +61 2 9144 3976