Ingersoll-Rand Thermo King SGCM 4000, Maintenance Manual, Page: 148 / 181

Alternator Operation and Diagnosis
147
Alternator Diagnosis
Preliminary Checks
WARNING: Extreme care must be used when working with an operating generator set. Lethal voltage
potentials exist inside the control box, at terminals on the DSR and at the power receptacle.
Before attempting the more complicated diagnosis procedures, check the following items to ensure a
superficial problem is not overlooked.
NOTE: Further diagnosis is a waste of time until these items are checked, since a problem in one of
these areas will influence test results.
1. If the generator malfunction is accompanied by excessive black exhaust smoke and engine lugging,
double check all possible engine problems such as fuel supply, injection timing, engine speed,
restricted air cleaner, etc.
2. Disconnect the refrigeration unit from the generator and check the output voltage at the plug. Voltage
between the three phases should be between 230 to 250 Vac or 400 to 500 Vac depending on engine
speed and whether the alternator stator is wired for 230 or 460 Volt operation. All three phases should
be within 3% of each other. If the voltages appear normal, make sure the refrigeration unit is not at
fault. Reconnect refrigeration unit and run in Cool mode. Check the amperage draw with an induction
type ammeter (amprobe), and compare it with the load plate on the refrigeration unit.
3. Check all push-in plugs on control circuits for loose pins or sockets. Make sure all wire terminals are
tight.
Test Instruments
If the preceding checks did not uncover the cause of the malfunction, more extensive diagnosis
procedures will be required. The following tests will require various electrical test instruments, and the
technician performing the tests should have a good working knowledge of their basic electrical principles.
The tests are intended to determine whether the source of difficulty lies in the generator itself or in the
excitation control system. Following the procedures carefully will, in many cases, avoid unnecessary
dismantling and reassembly of the generator when easily corrected problems may exist in the external
circuitry.
The test instruments required:
1. AC-DC voltmeter 2.5 Volts to 500 V ranges (± 2% max. error).
2. AC induction ammeter (amprobe).
3. DC ammeter (preferably induction type TK No. 204-947).
4. Ohmmeter.
5. Megohmmeter (Megger ® )
Alternator Troubleshooting
WARNING: When servicing or repairing a generator set, the possibility of serious or even fatal injury
from electrical shock exists. Extreme care must be used when working with an operating generator set.
Lethal voltage potentials can exist at the unit power cord, inside the exciter control box, inside any
high voltage junction box and within the wiring harnesses.
Normal alternator output voltage is 460 +/- 10 VAC with engine rpm 1890 +/- 10 rpm and no load
applied. If the generator produces no or low voltage output at the plug, perform the