VOLTAGEREGULATOR VOLTAGE REGULATOR OPERATION

To inspect the voltage regulator, remove it from the subbase and clean all the terminals and contact surfaces. Examine the base or housing for cracks. Check all connections for security. Remember that the voltage regulator is a precision instrument and cannot withstand rough treatment. Handle it with care. To adjust a voltage regulator, a precision portable voltmeter is required. This, too, must be handled with care, since it will not maintain accuracy under conditions of mishandling, vibration, or shock.

Detailed procedures for adjusting voltage regulators are given in applicable manufacturer's instructions. The following procedures are guidelines for adjusting the carbon pile voltage regulator in a multiengine 28 volt dc electrical system:

1. Start and warm up all engines which have installed generators.

2. Turn all generator switches to the "off" position.

3. Connect a precision voltmeter from the B terminal of one voltage regulator to a good ground.

4. Increase the engine speed of the generator being checked to normal cruising rpm. Operate remaining engines at idling speed.

5. Adjust the regulator until the voltmeter reads exactly 28 volts. (The location of the adjustment knob on a carbon pile voltage regulator is shown in figure 9-33.)

6. Repeat this procedure to adjust all voltage regulators.

7. Increase the speed of all engines to normal cruising rpm.

8. Close all generator switches.

9. Apply a load equivalent to approximately one-half full load rating of one generator when checking a two generator system or a load comparable to the rating of one generator when checking a system that has more than two generators.

10. Observe the ammeters or load meters. The difference between the highest and lowest generator current should not exceed the value listed in the manufacturer's maintenance instructions.

11. If the generators are not dividing the load equally (unparalleled), first lower the voltage of the highest generator and slightly raise the voltage of the lowest generator by adjusting the corresponding voltage regulators. When the generators have been adjusted to share the load equally, they are in "parallel."

12. After all adjustments have been made, make a final check of bus voltage from positive bus to ground, with a precision voltmeter. The voltmeter should read 28 volts, (±0.25 volt on most 28 volt systems). If the bus voltage is not within the proper limits, readjust all voltage regulator rheostats and recheck.

When inspecting the generator relay switch, examine the relay for cleanness and security of mounting and see that all electrical connections are tightly fastened. Look for burned or pitted contacts. Never close the relay manually by pressing the contacts together; this might severely damage the relay or cause an injury. Never adjust the differential type relay, since it closes when the generator voltage exceeds the system voltage by a specified value and is not checked to close at any set voltage; however, check it for proper closing by noting the ammeter indication with the battery generator control switches turned on while running the engines. It is sometimes necessary to put a slight load on the system before the ammeter will show a positive indication when the engine is run up to cruising speed. If the ammeter does not indicate, the relay is probably defective; therefore, remove it and replace it with a new relay. Check the reverse current relay for proper opening value. If the relay fails to close when the engine speed is increased or fails to disconnect the generator from the bus bar, the relay is defective.

Troubleshooting

If a generator system malfunctions, there are two general possibilities: (1) The generator itself may be at fault (burned out, damaged mechanically, etc.), or (2) that part of the circuit leading to or from the generator may be at fault. Continuity testing refers to checking for the existence of a complete electrical system between two points. The three main types of continuity testers are:

1. The portable dry cell tester, having a buzzer or a 3 volt lamp to indicate the completed circuit, is used to test circuits with the main circuit power off.

2. An ordinary lamp bulb (24 volt type), with one lead from the center lamp contact and one ground lead attached to the lamp housing, can be used to test circuits with the main circuit power on.

3. A precision voltmeter is used to test circuits with the main circuit power on by placing the positive lead on the circuit point and the negative lead on any convenient ground.

Tests should be made at each terminal of the circuit. Between the last point at which voltage is indicated and the first point at which zero voltage is indicated, there is an open circuit or a voltage drop caused by unit operation or short to ground. If the same voltage reading is obtained on the negative terminal of a unit as was obtained on the positive terminal, an open ground is indicated. If a small voltage reading is obtained on the negative terminal of the unit, a high resistance is indicated between the unit and ground.

The following troubleshooting chart outlines the most commonly encountered malfunctions, a list of probable causes to isolate the malfunctions, and the proper corrective action to be taken. This chart is a general guide for troubleshooting a twin engine dc generator system, which utilizes carbon pile voltage regulators.

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TROUBLE: No voltage indication on any one generator.

ISOLATION PROCEDURE: Check for defective generator switch or field switch.
CORRECTION: Replace generator switch or field switch.

ISOLATION PROCEDURE: Determine if generator polarity is reversed.
CORRECTION: Flash generator field.

ISOLATION PROCEDURE: Check for open, shorted, or grounded wiring.
CORRECTION: Replace defective wiring.

ISOLATION PROCEDURE: Check for defective generator.
CORRECTION: Replace generator.

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TROUBLE: Low voltage on any one generator.

ISOLATION PROCEDURE: Check voltage regulator adjustment
CORRECTION: Adjust voltage regulator.

ISOLATION PROCEDURE: Check for defective voltage regulator.
CORRECTION: Replace voltage regulator.

ISOLATION PROCEDURE: Check for defective wiring.
CORRECTION: Replace defective wiring.

ISOLATION PROCEDURE: Check for defective generator.
CORRECTION: Replace generator.

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TROUBLE: Generator cuts out.

ISOLATION PROCEDURE: Check for defective reverse current cutout relay.
CORRECTION: Replace reverse current cutout relay.

ISOLATION PROCEDURE: Check for defective overvoltage relay.
CORRECTION: Replace overvoltage relay.

ISOLATION PROCEDURE: Check for defective field control relay.
CORRECTION: Replace field control relay.

ISOLATION PROCEDURE: Check for defective voltage regulator.
CORRECTION: Replace voltage regulator.

ISOLATION PROCEDURE: Check for defective wiring.
CORRECTION: Replace defective wiring.

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TROUBLE: Voltage unsteady for any one generator.

ISOLATION PROCEDURE: Check for defective wiring.
CORRECTION: Replace defective wiring.

ISOLATION PROCEDURE: Check for defective generator.
CORRECTION: Replace generator.

ISOLATION PROCEDURE: Check wear of generator bearings.
CORRECTION: Replace generator.

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TROUBLE: No load indication on any one generator. Voltage is normal.

ISOLATION PROCEDURE: Check for defective reverse current cutout relay.
CORRECTION: Replace reverse current cutout relay.

ISOLATION PROCEDURE: Check for defective generator switch.
CORRECTION: Replace generator switch.

ISOLATION PROCEDURE: Check for defective wiring.
CORRECTION: Replace defective wiring.

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TROUBLE: Low dc bus voltage.

ISOLATION PROCEDURE: Check improper voltage regulator adjustment.
CORRECTION: Adjust voltage regulator.

ISOLATION PROCEDURE: Check for defective reverse current cutout relays.
CORRECTION: Replace reverse current cutout relays.

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TROUBLE: Voltage high on any one generator.

ISOLATION PROCEDURE: Check for improper voltage regulator adjustment.
CORRECTION: Adjust voltage regulator.

ISOLATION PROCEDURE: Check for defective voltage regulator.
CORRECTION: Replace voltage regulator.

ISOLATION PROCEDURE: Determine if generator field lead A is shorted to positive.
CORRECTION: Replace shorted wiring or repair connections.

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TROUBLE: Generator fails to build up more than approximately 2 volts.

ISOLATION PROCEDURE: Check voltage regulator or base. Take precision voltmeter reading between A terminal and ground. No voltage reading indicates trouble in either regulator or base. Reading of about 2 volts indicates regulator and base are OK.

CORRECTION: Check regulator contacts where they rest on the silver contact bar. Any signs of burning at this point is cause for replacement of regulator.

ISOLATION PROCEDURE: Check for defective generator. Low ohmmeter reading indicates current is good and trouble must be within the generator.

CORRECTION: Disconnect generator plug. Place one lead of ohmmeter on A terminal and the other lead on E terminal. High reading indicates that the generator field is open. Replace generator.

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TROUBLE: Instrument panel voltmeter reading of excessive voltage.

ISOLATION PROCEDURE: Check for short across A and B terminal of voltage regulator.
CORRECTION: If shorted, change voltage regulator.

ISOLATION PROCEDURE: Check voltage regulator control.
CORRECTION: Replace voltage regulator.

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TROUBLE: Instrument panel voltmeter reading of zero volts.

ISOLATION PROCEDURE: Check for defective voltmeter circuit.

CORRECTION: Place positive lead of voltmeter on positive terminal of instrument panel voltmeter and negative lead to ground. Reading should be 27.5 volts. If not, lead from regulator to instrument is defective. Replace or correct lead. Place positive lead of voltmeter on negative terminal of instrument panel voltmeter and negative lead to ground. If voltmeter reading is zero, instrument panel voltmeter is defective. Replace voltmeter.

ISOLATION PROCEDURE: Check for broken B or E lead. Remove voltage regulator and take ohmmeter reading between B contact finger of regulator base and ground. Low reading indicates circuit is OK. High reading indicates that a high resistance is the trouble.

CORRECTION: High resistance most likely is caused by oil, dirt, or burning at connector plug or commutator. Replace generator.

ISOLATION PROCEDURE: Check for loss of residual magnetism.

CORRECTION: Place flasher switch in ON position momentarily, Do not hold. NOTE: If flasher switch is held ON rather than switched momentarily, damage may be done to generator field coils.

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TROUBLE: Voltage does not build up properly when field is flashed.

ISOLATION PROCEDURE: Check for open field. Disconnect generator connector and take ohmmeter reading between A and E terminals of generator connectors. High reading indicates field circuit is open.

CORRECTION: Check and repair lead or connectors.

ISOLATION PROCEDURE: Check for grounded field. Take ohmmeter reading between A terminal of generator and generator housing. Low reading indicates field is grounded.

CORRECTION: Insulation on field winding is broken. Replace generator.

ISOLATION PROCEDURE: Check for open armature. Remove generator cover and inspect commutator. If solder is melted and has been thrown off, then armature is open (caused by generator overheating).

CORRECTION: Replace generator.

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