Ingersoll-Rand Thermo King SGCM 4000, Maintenance Manual, Page: 149 / 181

Alternator Operation and Diagnosis
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tests listed below to identify the component that may be causing a generator malfunction.
• Symptom: Low Output Voltage—0 to 100 Vac
NOTE: The DSR has a glass fuse (5AF 250 Volt) on the board. Check fuse if this fuse is blown
disconnect fan and replace fuse check output voltage.
Test 1 - Determine if problem is with the DSR or the Alternator
During the 2 minute delayed output, perform the following steps
1. Disconnect the radiator fan at the connector. This connector is found in the harness or at the terminal
block located in the junction box on the alternator (L1, L2, L3).
2. Open the junction box on the alternator and disconnect the Blue and Yellow wires from the DSR pins
1 and 2. Connect jumper wire with a 30 ohm resistor (1/2 watt) in series from 12 VDC positive to the
Yellow wire. Connect another jumper wire to the Blue wire
NOTE: Do not connect to ground yet.
3. Connect an AC volt meter to the output terminals U1 and V1.
• Start genset - engine will be in low speed.
4. Momentarily connect the jumper wire from the Blue wire to ground and monitor the output voltage.
Output voltage should be 400 VAC.
NOTE: If output voltage is not 400 VAC go to Test 2
5. If the output is 400 VAC,
a. Stop genset and check the resistance on the Quad winding.
b. Disconnect the Red wire on Pin 3 and Red wire to DSR wire,
c. Check resistance between the Red wires, should be 1.6 ohms.
d. If resistance is correct go to step 6.
6. Check the Quad relay circuit. Connect the ohm meter to the DSR wire and Quad wire. Turn genset on
and go to Commands/Manual Function Test, select Quad relay test. Observe if ohm meter turns relay
ON and OFF. If relay is working replace DSR.
Test 2- Alternator Exciter Field Testing
1. Disconnect the Blue and Yellow wires from pin 1 and 2 on the DSR field wire. Measure the resistance
of the field circuit (Blue to Yellow). The standard value is 9.7 (±10%) ohms at 77 F (25C). If field is
open or resistance value is low replace exciter field.
2. Measure Blue or yellow wires to GND for possible shorted to ground coils. Megger F1 to stator case
to check for insulation break down, @ 500 Volts must be more than 1 M ohm. If exciter field is OK,
go to test 3.
Test 3- Alternator Stator Testing
Test 3covers testing the main alternator stator, the rotating rectifier, the rotating exciter field, and the
rotating field armature.
1. Main alternator stator windings