Piper SARATOGA PA-32-301 Maintenance Manual page 186

PIPER AIRCRAFT
PA-32-301/301T
MAINTENANCE MANUAL
ALTERNATOR SYSTEM (90 AMP FORD)
DESCRIPTION OF ALTERNATOR. (Refer to Figure 24-16)
The principal components of the alternator are the Front Housing. Fan and Pulley. Rear Housing and
Terminal Identification. Stator Core and Coil Assembly. Rotor Core and Coil. Brushesand Holder Assembly
and Rectifier Assembly.
I. The front housing is a die-cast aluminum part which meets design requirements for a light-weight.
non-magnetic material. This casting incorporates the bosses used to attach the assembly to its mounting
bracket. It also provides the supporting surface for the rotor shaft front bearing and vendor identification data
stamped into the front housing.
The fan and pulley are attached to the rotor shaft with a nut and lock-washer. The forward end of the shaft
is threaded to accept the nut.
2. The rear housing is also a die-cast aluminum part which supports the rotor shaft rear bearing and
provides mounting bosses for the rectifier assembly. The housing contains the various electrical connections
and openings for cooling airflow. (Refer to Figure 24-17 for Terminal identification.)
3. The stator core and coil assembly consists of a number of steel stampings riveted together to form the
stator core which contains 36 equally spaced vertical slots to accomodate the stator coil windings. (Refer to
Figure 24-18.)
4. The rotor core and coil assembly consists of the rotor shaft. two slip rings. two rotor hal\ es and the
coil assembly. The shaft is supported at each end by bearings. The front bearing (ball-type) is a slip fit on the
shaft and is retained in the front housing with a retainer. The rear bearing (needle-type) is pressed into the rear
housing. The slip rings. core and coil assembly are press-fitted to the shaft with a rotor half enveloping each
end of the coil.
The rotor core and coil assembly turns inside the stator core and coil assembly with a very narrow air gap
between the two assemblies, thus developing maximum magneto induction.
5. The brush and holder assembly is installed in a cavity inside the rear housing. The brushes ride the
surfaces of the slip rings on the rotor shaft under spring pressure and transmit field current through their
circuit to ground. One brush or field terminal is. therefore. insulated from the housing.
6. The rectifier assembly is located between the stator and the inside surface of the rear housing.
Attachment to the housing is made by means of mounting studs that protrude from the positive and negati\e
diode plates (heat sinks). The positive plate is insulated from the housing. and the negative plate is grounded to
the housing through the studs. The rectifier assembly has a printed circuit board spaced away from the heat
sinks. (Refer to Figure 24-19.)
The stator winding leads are soldered to integral terminals on the back of the circuit board. The stator
phase top is attached to the insulated stator terminal. The heat sinks are attached to the circuit board with
insulated spacers and roll pins maintaining the necessary separation between the two assemblies. The diodes
themselves are exposed. The rectifier assembly has three diode plates connected to an AC potential. Each of
the three plates is connected to one of the three stator leads. Two steel conductor plates or "bus bars". one
positive and the other negative. circle the diodes beginning at the "BAT" and "GND" terminal studs. The bus
bars act as termination points for collecting the DC current from the terminal wire of each diode. One positive
and one negative diode is soldered to each of three stamped aluminum plates to form the plate and diode
assemblies. The aluminum plates serve as heat sinks to cool the diodes by providing increased surface area to
the air flow through sent slots in the rear housing to the fan at the front of the alternator.
One plate and d ode assembly is connected to each of the three leads to form the full wave bridge rectifier.
Diode terminal wires are connected to the bus bars by means of a flexible connector wire. One diode is
connected to the positive bus bar. and the other diode. on each plate. is connected to the grounded or negati e
bus bar. (Refer to Figure 24-20.)
EFFECTIVITY: FORD
24-32-01
Page 24-21
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Added: August 23. 1982
1H18