Piper COMANCHE PA-24-180 Service Manual page 545

PIPER COMANCHE SERVICE MANUAL
winding is reduced, the spiral spring tension pulls the armature up, the contact points close and
directly connect the genertor field to ground. Output increases and the above cycle is repeated.
The cycle continues to take place while the current regulator is in operation 50 to 200 times a
second, preventing the generator from exceeding its rated maximum. When the electrical load is
reduced (electrical devices turned off or battery comes up to charge), then the voltage increases
so that the voltage regulator begins to operate and tapers the generator output down. This pre-
vents the current regulator from operating. Either the voltage regulator or the current regulator
operates at any one time-the two do not operate at the same time.
9-25. Resistances.
The current and voltage regulator circuits use a common resistor which is
inserted in the field circuit when either the current or voltage regulator operates. A second re-
sistor is connected between the regulator field terminal and the cutout relay frame, which places
it in parallel with the generator field coils. The sudden reduction
in
field current occurring when
the current or voltage regulator contact points open, is accompanied by a surge of induced volt-
age in the field coils as the strength of the magnetic field changes. These surges are partially
dissipated by the two resistors, thus preventing excessive arcing at the contact points.
*(The second resistor is not present on all regulators. Many Aircraft regulators have this resistor
omitted.)
9-26. Temperature Compensation. Voltage regulators are compensated for temperature by means
of a bimetal thermostatic hinge on the armature. This causes the regulator to regulate at a higher
voltage when cold which partly compensates for the fact that a higher voltage is required to
charge a cold battery. Many current regulators also have a bimetal thermostatic hinge on the ar-
mature. This permits a somewhat higher generator output when the unit is cold, but causes the
output to drop off as temperature increases.
9-27. Regulator Polarity. Some regulators are designed for use with negative grounded systems.
while other regulators are designed for use with positive grounded systems. Using the wrong
polarity regulator on an installation will cause the regulator contact points to pit badly and give
short life. As a safeguard against installation of the wrong polarity regulator, all regulators of
this type have the model number and the polarity clearlystamped on the end ofthe regulator base.
9-28. Regulator Maintenance.
9-29. General Instructions.
a. Mechanical checks and adjustments (air gaps. point opening) must be made with battery
disconnected and regulator preferably off the aircraft.
CAUTION
The cutout relay contact points must never be closed by hand with
the battery connected to the regulator. This would cause a high
current to flow through the units which would seriously damage
them.
b. Electrical checks and adjustments may be made either on or off the aircrail The regulator
must always be operated with the type generator for which it :s designed.
ELECTRICAL SYSTE..
ISSUED: 8/18/72
3 A23