Usage:
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Take care when using meggers and high potential test equipment to check components. Improper use of such equipment could destroy the rectifiers, transistors and capacitors in the regulator. |
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Disconnect the leads between the regulator and generator when testing insulation resistance of generator windings with a megger.
Testing of components may be done with either an ohmmeter or an 8S4627 Continuity Circuit Tester.
Rectifier Test
Connect the ohmmeter or circuit tester across the rectifier. Observe the ohmmeter reading or whether or not the circuit tester bulb lights.
Reverse the leads and again observe the ohmmeter reading or whether the circuit tester bulb lights.
A good rectifier will have high resistance in one direction and low resistance in the opposite direction. If the circuit tester is used, the bulb should light in the direction where resistance is low, and should not light in direction of high resistance. If a low resistance is observed, or if the bulb glows, in both of the above tests, the rectifier is probably shorted and should be replaced. High resistance in both tests indicates an open rectifier and replacement is necessary.
RECTIFIER TEST PROCEDURE
Capacitor Test
Capacitors are best checked on a capacitance bridge that measures their value and leakage. Capacitors that vary more than ± 10% of their rated value should be replaced.
An approximate test of a capacitor may be made with an ohmmeter set on a high resistance scale. The meter will initially indicate a low resistance and then gradually increase until the capacitor is fully charged.
Saturable Transformer Testing
Typical defects found in any type of transformer are open and shorted windings. Open windings are easily determined by disconnecting the transformer from the circuit and testing for continuity with an ohmmeter. Shorted windings or shorts between windings are more difficult to determine. A resistance check can be made and compared against those of a transformer known to be good. However, the best policy is to replace a transformer that is suspect.
Power Transformer Test
Disconnect the secondary windings. Start the engine and increase RPM until rated voltage is measured across the primary.
Measure the output voltage across the secondary.
NOTE: It may be necessary to exceed rated RPM about 10% in order to obtain rated voltage in the primary. Exercise extreme caution during this test.
Since the resistance of the windings in most transformers is so low, it is often very difficult to locate a problem with an ohmmeter. If the transformer has overheated, the fault may be shorted turns. In this case, check the no-load alternating current in the primary. Disconnect the secondary from the load. There will be excessive current in the primary if there are shorted turns.
Current Transformer Test
Current transformers have a fixed ratio of current between the primary and the secondary. This ratio is determined by the ratio of winding turns. The following test may be made to check for shorted turns:
1. Load the generator to produce primary current in the transformer.
2. Measure the secondary current.
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Do not open the secondary circuit of a current transformer when the circuit is energized. |
The ratio of primary to secondary current is approximately the same as the ratio of secondary turns to primary turns. If secondary current is considerably less than it should be, shorted turns are indicated.
Rheostats And Resistors
Check the resistance values of these components with an ohmmeter. Rheostats and adjustable resistors should be checked over their entire range. Care should be taken to avoid damage to the fine wire when setting adjustment bands on adjustable resistors. The adjustment band should be loosened until it slides freely on the resistor tube.
Silicon Transistor Test
Silicon transistors can be tested for opens or shorts using the 8S4627 Continuity Circuit Tester. Remove the transistor from the circuit to prevent other components from affecting the indicators. The light indications shown in the chart are those which should be observed if the transistor is not shorted or open.
Testing Rotating Rectifiers (Diodes)
If a failure of one of the rotating rectifiers (diodes) is suspected, remove the generator cover and test the rectifier (diode) with an ohmmeter.
NOTE: The 8S4627 Continuity Circuit Tester may be used in lieu of an ohmmeter.
1. Remove the nut and washer holding the diode in the heat sink. Remove the lead from the diode and remove the diode from the heat sink.
2. Connect the ohmmeter (or tester) leads across the rectifier in one direction. Note the meter reading (or whether the light glows or not). The meter should indicate a low resistance in one direction and a high resistance in the opposite direction. (Light will burn in one direction and not in the other.)
3. If a low resistance indication is obtained in both directions the diode is shorted. A high resistance in both directions indicates an open. In either case, the rectifier (diode) must be replaced.
ROTATING RECTIFIER (DIODE) LOCATION
1-Rectifiers (Diodes).
Surge Protector Test
Use the same procedure for testing the surge protectors as outlined for the rotating rectifiers. However, a very high value of resistance should be indicated in both directions. The test lamp should not light in either direction. A low value of resistance (or a glowing lamp) indicates a short. Replace the surge suppressor in this event.
SURGE SUPPRESSOR LOCATION