External rotor motors drive all of the Ecofit fans and most of the Rosenberg fans.
Unlike conventional motors whose rotors are on the inside of a wound stator, external rotor motors have their rotor on the outside. This presents unique advantages to the fan manufacturer and user as detailed below:
- An extremely compact, therefore space saving unit, is produced by utilising the external rotor component as the hub of a fan impeller.
- Precision balancing is assured as the hub and impeller becomes one integrated unit of short axial length.
- Heat is very effectively removed in the airstream, assisted by the fan impeller that acts as a rotating heat sink of appreciable surface area.
- Speed control is then possible by low cost voltage variation because the extra heat generated in the rotor under speed control is lost directly into the airstream.
- Air filters can be 'saved' when clean but 'air flow compensated' when dirty by the tendency of centrifugal fans to speed-up as flow resistance increases. The increase in speed is more pronounced when using external rotor motors.
- In general the external rotor principle leads to small efficient motors, ideal for saving space within equipment.
