Basic Operation
Bidirectional motors - those that can rotate in either direction – are
of two classes:
1. Reversing motors
, which can change from full
speed in one direction to full speed in the opposite direction.
2. Reversible motors
, which can be reversed only when the motor
is not running, or is running below cut out speed. Some motor
manufacturers distinguish between quick reversing and instant
reversing. A quick reversing motor requires a time delay of
approximately 1/25th of a second or more for the switching circuitry
to react. An instant reversing motor requires absolutely no time
delay. The standard SINPAC Switch can be used on reversible and
reversing motors. The SINPAC IR Series Switch provides the
function of a direction sensing centrifugal switch and makes a
reversible capacitor start motor into an instant reversing motor.
In order to reverse a single-phase motor, it is necessary to reverse
the polarity of either the start or main winding, but not both at the
same time. The reversal of the winding is accomplished with an
external reversing switch or contactor that is not part of the SINPAC
Switch. SINPAC Instant Reverse Switch is not dependent upon how
quickly the user operates the reversing switch, but only that the
reversing switch did change states, i.e., forward to reverse, or vice
versa. The SINPAC Switch detects the change in the phase shift
between the main and start windings, and the logic circuit instantly
actuates the starting switch, causing the
start circuit to be reconnected to line
voltage. This connection causes the
motor to decelerate and then
reaccelerate in the opposite direction.
The SINPAC IR Series Switch interrupts
the start circuit current after the motor
has accelerated to the cut out speed, and
reconnects the start circuit whenever the
circuit senses the motor speed has fallen
to cut in speed (usually about 50% of
synchronous motor speed).