Service Manual

Table Of Contents
6. Service 10-2019
112 A062J683 (Issue 1)Copyright © 2019 Cummins Inc.
NOTICE
Make sure that the brushes are aligned correctly with the slip
rings; otherwise, the brushes may break when the generator set
is started.
b. If the slip rings have grooves, pits, or other damage, use a Scotch Brite
pad or commutator stone to remove light wear or corrosion.
6. Re-install the brush block cover.
Testing the Alternator
1. Rotor Winding Continuity:
a. Test the rotor for grounded, open and shorted windings using an
ohmmeter, testing at the brush block terminals first.
b. If the resistance is high, remove the brush block and test directly on the
slip rings.
c. Replace the brush block if a high resistance is due to the brushes.
2. Rotor Ground Resistance Test:
a. Set the ohmmeter to the highest resistance scale, or use a megger.
b. Touch one test probe to the rotor shaft and the other to one of the slip
rings.
c. Refer to the table below for resistance values. If test values do not match
measurement values, replace the alternator.
TABLE 14. ROTOR AND STATOR RESISTANCE TESTS
Tests Measurement Values
Rotor Ground Resistance Reading > 1 megohm (one million Ohms) on
megger, or infinity on an ohmmeter
Rotor Winding Resistance F1 to F2 (at 24 °C
[75 °F] room temperature)
13 kW = 26 +/– 10% Ohms
17/20 kW = 30.5 +/– 10% Ohms
Main Winding to Quad Winding Open (infinity) for any winding
Stator Ground Resistance Reading > 1 megohm (one million Ohms) on
megger, or infinity on an ohmmeter.
Stator Winding Resistance (at 24 °C [75 °F]
room temperature):
L1 to N
13 kW = 0.112 +/– 10% Ohms
17/20 kW = 0.042 +/– 10% Ohms
L2 to N
13 kW = 0.112 +/– 10% Ohms
17/20 kW = 0.042 +/– 10% Ohms