Caterpillar — VR3 Regulator Adjustment Procedure

Adjustments · VR3 Voltage Regulator

From a Caterpillar owner's manual covering: 3306B, 3406, 3406E, 3412C, SR4B. Check it applies to your exact model before use.

Applies to: Caterpillar 3306B, Caterpillar 3406, Caterpillar 3406E, Caterpillar 3412C, Caterpillar SR4B

Procedure

1. Remove the access panel of the generator.
2. Loosen the locknut on the voltage droop potentiometer (1).
3. Remove the protective screw from the voltage level potentiometer (2) and from the voltage gain potentiometer (3).
4. Turn the voltage droop potentiometer (1) counterclockwise to zero droop. Tighten the locknut.
5. Turn the voltage gain potentiometer (3) counterclockwise to zero, then to about 1/4 of full range of clockwise travel.
6. Perform required maintenance on the engine before you start the engine.
7. Start the engine and allow the engine to warm up.
8. Increase engine speed to full governed rated speed (high idle).
9. Set the no-load voltage with the voltage level potentiometer (2) or the voltage adjust rheostat.
10. Close the load circuit breaker and apply full load gradually. Adjust governor control to nameplate frequency or rated speed.
11. If the voltmeter reading increases above no-load voltage, turn the voltage gain potentiometer counterclockwise. If it decreases, turn it clockwise.
12. Remove the load. If necessary, adjust the voltage level potentiometer (2) to obtain desired voltage.
13. Apply the load. Repeat Steps 10 through 12 until the voltage at no load equals the voltage at full load.
14. Tighten the locknuts. Install the protective screws and the access panel of the generator.

Full service-parts list: Caterpillar 3406 →, Caterpillar 3406E →, Caterpillar 3412C →, Caterpillar SR4B →

Source: Caterpillar owner's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.

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