Piper CHEROKEE WARRIOR PA-28-151 1995 Maintenance Manual page 391

PIPER CHEROKEE WARRIOR SERV I C E M A N U A L
b . Rectifiers: A diode rectifier tester will detect and pinpoint open or shorted rectifiers without
d i sconnecting stator leads. On both the 12 Vdc and 24 Vdc alternators, if a tester is not available, test probes
and a no. 57 bulb, connected in series with a 12 volt battery can be used as follows:
1 Touch one test probe to a rectifier heat sink and the other test probe to a lead from one of the
rectifiers in that heat sink.
2 Reverse position of the leads.
Test bulb must light in one direction and not light in the other
direction. If test bulb lights in both directions, one or more of
the rectifiers in that heat sink is shorted.
3 To pinpoint defective rectifier, stator leads must be disconnected and above test repeated on
each rectifier.
Open rectifiers can only be detected, when using test bulb, by
disconnecting stator leads. Test bulb will fail to light in either
direction if rectifier is open.
c. Stator: The stator is tested for open or grounded windings with a 12-volt test bulb, described in
rectifier section, or an ohmmeter, as follows:
1 Separate stator from slip ring end head just far enough to insert a fold of rags or block of wood
(insulate stator from end head).
2 Test for grounded windings by touching one test bulb or ohmmeter probe to auxiliary terminal
or any other stator lead, and the other test bulb or ohmmeter probe to stator frame. If test bulb lights, or
o h mmeter indicates continuity, stator is grounded.
3 Test for open windings by connecting one test probe to auxiliary terminal or stator winding
center connection, and touch each of three stator leads. (Test bulb must light, or ohmmeter must show continuity.)
Due to low resistance in stator windings, shorted windings are
difficult to locate. Shorted stator windings will usually cause
alternator to growl or be noisy during operation, and will usu -
ally show signs of overheating. If all other electrical checks
are normal and alternator fails to supply its rated output, sta -
tor must be replaced to determine if it is the faulty component.
d. Bearings and seals: When alternator is overhauled, new bearings and oil or grease seals are recom-
mended (even though bearings and seals may appear to be in good condition).
A faulty seal will cause alternator to fail within a very short
period of time.
Revised: February 28, 1995
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2E8
Island Enterprises
ELECTRICAL SYSTEM