VOLTAGE REGULATOR ADJUSTMENT

PREVENTIVE MAINTENANCE - TM-5-3820-256-24-4_351

TM-5-3820-256-24-4 Drilling System Well Rotary Truck Mounted Air Transportable 600 Feet Capacity Model LP-12 NSN 3820-01-246-4276 Manual
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HEAVY DUTY ALTERNATORS 7. If the alternator is found to be OK or if an "overcharging" condition exists, then the regulator must be adjusted. See VOLTAGE REGULATOR ADJUSTMENT. NOTE - If the alternator Is equipped with a "fixed voltage" (non-adjustable) regulator, then adjustments cannot be made. If the alternator is found to be OK, the "fixed voltage" regulator must be replaced. If adjustment has no effect on the output voltage, the regulator must be replaced. 8. To establish which component is causing the alternator to malfunction, perform an AC voltage test. The batteries must be fully charged and a 12-volt test lamp is needed to perform this test. The test lamp can be made of a two filament headlight unit, with both filaments wired in parallel. The lamp acts as an indicator as well as a load. With all electrical accessories off, run the engine at about 1000 RPM and connect the test lamp across the three AC terminals as shown in Figure 4. If the test lamp does not light, or if it lights with equal intensity on each phase, then the rotor is probably faulty. If one or two test points result in a dimmer light, then either the stator or a power diode is defective. Figure 4 - AC Voltage Test. The voltage regulator used in these alternators is a solid state device and for this reason will normally have an extremely long life. It can, however, be damaged by mechanical or electrical abuse. If the system polarity is inadvertently reversed by installing a battery backwards, boosting or jump starting with the jumper connected backwards, or reversing the positive and negative alternator output leads when changing an alternator, the voltage regulator will be damaged. Although the polarity reversal may only be momentary and may not damage the alternator diodes, the regulator will still be damaged. VOLTAGE REGULATOR ADJUSTMENT NOTE - This procedure applies to alternators with adjustable regulator. If the alternator Is equipped with a "fixed voltage" regulator, adjustment cannot be made. 1. Check the drive belts, wiring, and mounting hardware, and make sure that they are in proper working order. 2. Check the batteries according to manufacturer’s specifications to insure that they are in good condition. The batteries must be fully charged. If necessary, charge or replace batteries. 3. To adjust the regulator, shut off all electrical accessories and run the engine at about 1000 RPM. Check the voltage across the alternator output terminals. Remove the plastic screw from the regulator and engage a small screwdriver with the adjustment screw inside the access hole (Figure 5). CAUTION - TO AVOID DAMAGING REGULATOR, DO NOT EXERT EXCESS PRESSURE ON THE ADJUSTMENT SCREW. Figure 5 - Adjusting Voltage Regulator. Turn the adjustment screw CLOCKWISE TO RAISE voltage or COUNTERCLOCKWISE TO LOWER the voltage. CAUTION - TO AVOID DAMAGING REGULATOR, DO NOT FORCE THE ADJUSTMENT SCREW PAST THE STOPS AT EITHER END OF THE ADJUSTMENT RANGE. Voltage should be set between 13.8-14.2 volts (or 14.0 volts nominal setting ± 0.2 volts). Reinstall the plastic CTS-4043A - Chapter II - Page 4

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