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M-2
CONTROLLERS, VSD, SENSORS & RUN-ON TIMERS
CONTROLLERS, VSD, SENSORS & RUN-ON TIMERS
© FANTECH
2016
INTRODUCTION
SPEED CONTROL
Air capacity control of fans is most efficiently achieved by controlling the fan speed.
The principle benefits to be gained are:-
O
control of noise
O
control of power absorbed
There are a number of methods that can be used to do this, including:-
O
star/delta 2 speed switches
O
triac speed controllers (example VA and AVA speed controllers....
Ref. Pg. M5
)
O
Variable speed drives (frequency inverters)
O
multi-speed motors
There are many applications where the full capacity is required for only a short period
of time and if no speed control system is available, there is an unnecessary loss of
heated or conditioned air or wasted energy taking place. In addition, there are
substantial reductions in fan noise and power that can be obtained.
Controlling the speed of a fan by means of changing the supply voltage with a triac
speed controller is a simple and often-used method, but it does require certain
conditions to be fulfilled:-
O
the motor must have a high resistance rotor (single phase)
O
the motor must have above average cooling
However a triac controller is not an efficient method of speed control.
Note: If more than one fan is to be connected to a single controller, the fans must be
identical. Dissimilar fans should not be connected to the same controller and never to
multiple multi-speed motors.
When using a speed controller on a single multi-speed single-phase fan, always set or
connect fan to "high".
SPEED CONTROL OF EXTERNAL ROTOR MOTORS
External rotor motors generally have a high resistance rotor as an inherent feature of
their design.
In addition the cooling of these motors is very efficient, so these motors meet the basic
requirements necessary for speed control by triac control.
With triac control, heat is generated in the rotor, particularly at around two thirds of full
speed. This heat is then transmitted directly to the impeller mounted on the motor and
hence into the surrounding air without adding additional thermal stresses on the stator.
Therefore unless otherwise stated, motors operating with a speed-controller should not
be run in ambient temperatures exceeding 40ºC.
STAR/DELTA CONTROL
The three-phase external rotor motors fitted to backward-curved centrifugal fans have
star/delta motors fitted to them as standard. This facility enables two speeds to be
obtained using either a star/delta switch such as the SD1-S or star/delta controller.
In addition some axial fans, such as SCD and CPD fitted with conventional motors,
have the star/delta feature.
The speed ratio obtained with the star/delta feature is approximately 1.3:1.
M