Refer to the "Varistor Test" section of this document for test procedures. If any meter reading does not fall within the given range, replace the heat sink assembly. Refer to the "Removal/Installation Instructions" section.
- In order to perform this diode check, the diodes must be isolated, that is, the diodes must be disconnected. Refer to Illustration 1.
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Illustration 2 g02175388 - Attach a battery and a light to each diode in both directions in order to test the diode. Refer to Illustration 2.
- Replace the diodes that illuminate the light bulb when wired in both directions.
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| Illustration 1 | g01327476 |
Check the Windings and Rotating Diodes by use of Separate Excitation
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During this procedure, make sure that the generator is disconnected from any external load. Inspect the terminal box to check that the connections are fully tightened. |
- Stop the unit, disconnect, and isolate the AVR wires.
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Illustration 3 g01327528 Show/hide table
Illustration 4 g01327530 - There are two ways of creating an assembly with separate excitation. Assemble one of the following test circuits.
Note: The voltage of a 12 V battery or a 24 V battery is too high for the required excitation voltage when running at rated engine speed. A Variac or a rheostat must be used in order to adjust the required excitation current for the nominal voltage at no load. Refer to Illustration 3. Refer also to Illustration 4.
As an alternative, a 12 V battery that is directly connected may be used if running the engine at low idle speed. Refer to "Generator Set - Test" section of this publication.
Both these systems should have characteristics which are compatible with the machine field excitation power. Refer to the nameplate.
- Run the generator at the recommended speed that is used during normal operations.
- Gradually increase the exciter field current. Adjust the rheostat or the Variac. Measure the output voltages on "L1- L2 - L3". Check the excitation voltage and the current at no load and with a load. Refer to the machine nameplate or ask for the factory test report.
- The machine is in good working order if the following conditions are true:
- Output voltage is at the rated value
- Output voltage is balanced within 1% for the rated excitation level
The fault therefore comes from the Cat DVR or the associated wiring. Associated wiring includes sensing or auxiliary windings.
Rectifier Assembly Troubleshooting Checklist
| Package S/N: | |
| Factory Claim Number | |
| Service Request Number | |
| Dealer Contact - Name and Phone | |
| External varistor check | Installed (Y / N) - |
| Megohmmeter measurement (VDC) - | |
| Condition (Good/Bad) - | |
| Internal varistor check | Megohmmeter measurement (VDC) - |
| Condition (Good/Bad) - | |
| Diode check | AC1 AC2 AC3 |
| Forward Biased Check - Pos. (VDC) - | |
| Forward Biased Check - Neg. (VDC) - | |
| Reverse Biased Check - Pos. (VDC) - | |
| Reverse Biased Check - Neg. (VDC) - | |
| Exciter Rotor check | Insulation test results (Megohms) - |
| Winding test results (Ohms) - | |
| Main Rotor check | Insulation test results (Megohms) - |
| Winding test results (Ohms) - | |
| Other Failed Parts (Regulator, Exciter Stator, Exciter Rotor) | |
| Failure Analysis Root Cause/Time Line of event |