Piper COMANCHE PA-24-180 Service Manual page 543

PIPER COMANCHE SERVICE MANUAL
9-21. Regultors. The regulator shown in Figure 9-3 consists of a cutout relay, a voltage regu-
lator, and a current regulator unit. The cutout relay closes the generator-to-battery circuit when
the genertor voltage is sufficient to charge the battery, and it opens the circuit when the gener-
ator slows down or stops. The voltage regulator unit is a voltage-limiting device that prevents
the system voltage from exceeding a specified maximum and thus protects the battery and other
voltage-sensitive equipment. The current regulator unit is a current-limiting device that limits the
generator output so as not to exceed its rated maximum.
9-22. Cutout Relay.
a. The cutout relay (Figure 9-3) has two windings, a series winding of a few turns of heavy
wire and a shunt winding of many turns of fine wire (shown in dashed lines). The shunt winding
is connected across the generator so that generator voltage is impressed upon it at all times. The
series winding is connected in series with the charging circuit so that all generator output passes
through it. The relay core and windings are assembled into a frame. A flat steel armature is at-
tached to the frame by a flexible hinge so that it is centered just above the and of the core. The
armature contact points are located jut above the stationary contact point:
When the generator
is not operating, the armature contct points are held way from the stationary points by the ten-
sion of a flat pring riveted on the side of the armture.
b. When the generatr voltage builds up a value great enough to charge the battery, the mag-
netism induced by the relay windings is sufficient to pull the armature toward the con so that the
contact points close. This completes the circuit between the generator and battery. The current
which flows from the generator to the battery passes through the series winding in a direction to
add to the magnetism holding the armature down and the contact points closed.
c. When the generator slows down or stops, current begins to flow from the battery to the
generator.
d. This reverse flow of current through the series winding causes a reversal of the senes
winding magnetic field. The magnetic field of the shunt winding does not reverse. Therefore, in-
stead of helping each other, the two windings now magnetically oppose so that the resultant mag-
netic field becomes insufficient to hold the armature down. The flat spring pulls the armature
away from the core so that the points separate this opens the circuit between the generator and
battery.
9-23. Voltage Regulator.
a. The voltage regulator (Figure 9-3) has two windings assembled on a single core, a shunt
winding consisting of many turns of fine wire (shown in dashed lines) which is shunted across
the genertor, and a series winding of a few turns of relatively heavy wire which is connected in
series with the generator field circuit when the regulator contact points are closed.
b. The windings and core are ssembled into a frame. A flat steel armature is attached to
the frame by a flexible hinge so that it is just above the end of the core. The armature contains a
contact point which is just beneath a stationary contact point. When the voltage regultor is not
operating, the tension of a spiral spring holds the armature away from the core so that the points
are in contact and the generator field circuit is completed to ground through them.
c. When the generator voltage reaches the value for which the voltage regultor is adjusted,
the magnetic field produced by the two windings (shunt and series) overcomes the armature spring
tension and pulls the armature down so that the contact points separate. This inserts resistance
into the generator field circuit so that the generator field current and voltag are reduced. Reduc-
tion of the generator voltage reduces the magnetic field of the regulator shunt winding. Also,
ELECTRICAL SYSTEM
ISSUED: 8/18/72
3 A21