Thermo King SGCO 3000, Manual

Page: 117 / 144

Alternator Operation and Diagnosis
117
Alternator Diagnosis
Preliminary Checks
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
Listed below are the categories in which most
generator malfunctions will fall. Following each
category are a number of possible component
failures that may cause the malfunction. Listed
with each component is the test used to check the
component.
NOTE: Always use Test 1 first to determine if the
alternator or the controller is at fault.
1. Generator set has low or no output voltage
(system overload).
a. Controller is not exciting alternator
(Test 1).
b. Exciter field circuit in alternator is open
circuit (Test 4).
c. Alternator stator, main rotating field,
rotating rectifier or rotating exciter
armature is defective (Test 5).
2. Generator set tries to pick up the load but
engine labors excessively, eventually causing
a system overload condition.
a. Mechanical problems with engine (see
preliminary check 1).
b. Excessive load from refrigeration unit
malfunction (see preliminary check 2).
c. Defect in controller, rotating field, rotating
bridge, alternator main field or alternator
stator (Test 1 and Test 5).
3. Unit battery undercharged.
a. Battery defective.
b. Fuse SI2 bad.
c. Controller fault (Test 2).