35. DC to AC Rotary Converter. -A rotary converter, in effect, is a motor-generator set built on one frame. The same field is used for both the motor and the generator, and the operation of the machine depends upon the generated voltage in
any DC motor as described in the beginning of this chapter. The armature has a
commutator on one end and is tapped, and connections are brought out to slip rings
on the other end. Power is supplied to the direct current end (the commutator
end) of the armature. As the machine rotates, an alternating current flows in
the armature, and is brought out through the slip rings to the power supply.
Such a machine is much simpler in construction and operation than the DC to AC
motor-generator sets just described. The rotary converter used with Photophone
equipment was specially constructed for such use, as the ordinary rotary converter
run from a 125 volt DC line would not supply, the voltage required by the power
amplifier unit.
A rotary converter which may be used in any installation where the
1/2 k-va. motor-generator set may be used is illustrated in Figure 30. The DC commutator
is at the left and the slip rings of the AC end are at the right. To oil the machine,
which should be done once a week, it is necessary to remove the oil well covers at
each end of the converter by means of the two screws provided. The bearings are
waste packed, and the waste should be kept well saturated with oil. At the time
of oiling, the commutators and slip rings should be inspected and cleaned if
necessary.
In Figure 31 is illustrated the 1 1/2 k-va. rotary converter which may be used in
any installation where the 1 1/2 k-va. motor-generator set may be used. This converter is similar to the
3/4, k-va. converter except for its size. On account of its
increased size a starting box is used. This starting box is the same as that described
for the 1 1/2 k-va. motor-generator set. The 1 1/2 k-va. rotary converter has oil ring
bearings similar to those described in the discussion of the AC to DC motor-generator sets for DC projector drive motors. The level of the oil in the oil cups should
be checked once a week and maintained about 1/8 of an inch from the top of the oil
cups. The commutator of the 1 1/2 k-va. converter should be checked weekly and
cleaned with 00 sandpaper when necessary. Both converters contain, on the commutator end of the armature, a blower for the purpose of ventilation.
23
