Lincoln Electric SAE-300 HE Service Manual page 35

LINCOLN ELECTRIC
EXCITER ROTOR RESISTANCE AND GROUND TEST PROCEDURE
(Exciter / Auxiliary Power Alternator)
Service and repair should be performed by only Lincoln Electric factory trained personnel. Unauthorized
repairs performed on this equipment may result in danger to the technician or machine operator and will
invalidate your factory warranty. For your safety and to avoid electrical shock, please observe all safety
notes and precautions detailed throughout this manual. If for any reason you do not understand the test
procedures or are unable to perform the test/repairs safely, contact the Lincoln Electric Service Department
for electrical troubleshooting assistance before you proceed. Call 1-888-935-3877.
TEST DESCRIPTION
This test will determine if the Exciter / Auxiliary Power Alternator Rotor Winding is open, shorted, or
grounded.
MATERIALS NEEDED
Volt/Ohmmeter (Analog Type Meter Best For Dynamic Resistance Test)
Wiring Diagram
TEST PROCEDURE
Static Tests:
1. Turn off the engine on the SAE-300 HE machine.
2. Lift the left and right side covers and secure them with the hooks provided.
3. Remove the cover from the exciter / auxiliary power alternator by removing the screws securing it.
4. Label and disconnect the leads connected to the rotor brush holder assembly. See Wiring Diagram.
Remove the leads to electrically isolate the rotor windings.
5. Using a volt/ohmmeter, measure the rotor winding resistance across the slip rings. Normal
resistance is approximately 40* ohms, at 77°F. (25° C.). See Figure F.9.
6. Using a volt/ohmmeter, measure the resistance to ground. Place one meter probe on either of the
slip rings. Place the other probe on any good, unpainted chassis ground. The resistance should be
very high, at least 500,000 (500k) ohms.
If the resistance measurements are not as specified the rotor may be faulty and should be replaced.
If these resistance values are normal, continue testing, using the dynamic rotor resistance and
ground test.
Dynamic Tests:
(Also referred to as flying resistance test)
This test checks for faults in the rotor winding, while these windings are being stressed by the
mechanical forces encountered during normal operation.
NOTE: This test is best performed with a good quality analog type ohmmeter. Many digital meters
will not provide stable or accurate resistance readings while the rotor is spinning.
This test requires that the brushes and slip rings are clean, in good condition and are properly
SAE-300® HE Service Manual
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