TM11-6125-256-34
4-30. Voltage and Frequency Potentiometer
c The face of each ship ring brush should contact its
slip ring for at least 75 percent of the brush area
Spread
d There should be no evidence of excessive grooving
a Apply a 27 5-volt dc input and a no-load output
or other surface damage to the face of the brushes
b Monitor output voltage and adjust the voltage
adjust potentiometer (fig 3-1) fully counterclockwise and
then fully clockwise Output voltage, at minimum, must
vary between 110 and 120 volts Adjust output voltage to
a Apply a 27 5-volt dc input and a no-load output
116 volts
c. Monitor output frequency. Frequency
must be 400 Hz 10 Hz. See paragraph 3-5.
4-31. Commutation Test
b Measure the shunt field current and then remove
input power
a Remove the dc brush access covers
c Loosen the screws securing the dc end bell assembly
b Apply a 26-volt dc input and a no-load output
to the housing.
Observe brush commutation The commutation must
produce only fine pin points
d Shift the dc end bell assembly for minimum shunt
c Apply a 3-phase, 5000-watt unity power factor load
field current at no load and for the best commutation at
The commutation must produce only fine pin points
full load
d Repeat step b and c with a 29-volt dc input The
e Tighten the dc end bell assembly screws
commutation must produce only fine pin points
f Drill and install spring pins (71, fig FO-3) to retain
e Turn off input power and install the dc brush access
the end bell assembly setting
covers
