The electrical connections to the motor are made in the metal box, in which
the starting resistor is mounted, on the end of the motor. Four leads are brought
out into this box from the motor, two of which are connected to the running winding and two to the starting winding. The leads from the running winding are
connected to the two binding posts provided for power connections, and the starting winding is connected to the left-hand binding post and to the left-hand end of
the starting resistor. If these two last named leads are reversed the direction of
rotation of the motor will be reversed, as such a connection will reverse the "phase
relation" between the starting and running windings. The running winding will
keep the motor running in either direction once it is up to speed.
This motor utilizes waste-packed bearings which should be oiled about once a
week with a medium grade of machine oil. The oil hole for one bearing is underneath the motor terminal and resistor box, and must be reached through the channel provided in the bottom of the terminal box for such a purpose.
(C) CONVERTING EQUIPMENT
33. AC to DC M-G Sets for Driving DC Projector Motors. -An AC to DC M-G
set is used to supply DC power for driving projector motors when either 25 cycle or
50 cycle two-phase or three-phase power is the standard power supply at the
theatre; or where 60 cycle three-phase power is standard power supply for the
theatre, but it is desirable to have a variable speed projector drive motor.
The purpose of the M-G set is solely that of supplying power to the projector
drive motor. Two M-G sets are usually supplied for one installation, one of the sets
being a stand-by machine for emergency service. See Figure 23.