Fault

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FAULT FIN D I N G GUI D E BRU S H L E S S CAPA C IT O R TYPE ALTER N A T O R S BEF O R E PRO C E E D I N G , IT IS IM P O R T A N T TO RE M E M B E R THAT CHEC K S AN D FAULT FIN D I N G SH O U L D ONL Y BE CAR R I E D OUT BY A CO M P E T E N T TRAI N E D ENGI N E E R, USI N G THE COR R E C T TOOL S AN D EQUIP M E N T .

NO VOLTA G E OUTPUT. 1) The voltage output of a brushless capacitor type alternator is dependant on the rotational speed of the engine. For a 50HZ generator this should be as follows; No- load; Full-load;

3100 - 3150 rpm ( 51.5 - 52.5 hz ). Nominally 3000 rpm ( 50hz).

Before commencing checks it is important to verify that the engine rpm is correct. 2) Check that circuit breakers have not tripped and that they are in working order. 3) The alternator control box lid and non- drive end covers should now be removed, allowing a visual inspection to be carried out. Check that all connections within the control box are secure, and that there are no broken wires etc. Make a visual check of the alternator windings for signs of burning. The discovery of a broken wire or burnt out winding at this stage, can save a lot of time and effort ! 4) Check capacitor and if unserviceable, replace with one of the same voltage and micro farad value. Note; dis- charge used capacitor by shorting terminals before handling. 5) Try to re-excite generator by applying a 12vdc external supply (battery) across the capacitor terminals (with capacitor connected) for a few seconds. This should be done with the generator running at nominal speed with no- load applied. 6) Check continuity and value of alternator stator windings in accordance with manufacturer’s data; a) Check continuity / resistance of auxiliary (capacitor) winding with capacitor disconnected. b) Check continuity / resistance of main stator winding. Resistance of two halves of main winding should be equal to within 0.5 ohm. Continued.......

c) Check for a breakdown in winding insulation by carrying out following resistance tests; Check auxiliary winding to earth Check main winding halves to earth Check between both halves of main winding and auxiliary winding. Ideally, insulation checks should be made with a high voltage tester (meggar) at 500 volts. All insulation resistance readings should be greater than 1 mega ohm.

LOW VOLTA G E OUTP UT. 1) Check and verify correct rotational speed. 2) Check and verify that generator is not being overloaded. Overload = lower engine rpm = low voltage. 3) Check that alternator shaft securing stud is tight and that rotor is not slipping on engine taper. 4) Check rotating diodes for open or short circuit. This is done by un- soldering one end of the diode and checking with an ohm meter or diode tester for continuity in one direction only (refer to manufacturer’s handbook). Note; If a defective diode is found, it is advisable to replace both components. When replacing a diode ensure that it in inserted in the correct polarity. 5) With diodes disconnected, check rotor winding for continuity and resistance. Refer to manufacturer’s data for resistance values. 6) Low voltage can also be caused if a capacitor of low micro- farad value has been fitted.

UN ST A B L E VOLTA G E OUTP UT . 1) Check for constant engine speed. As we know, the voltage is dependant on rpm - unstable or fluctuating rpm = unstable / fluctuating voltage output. 2) Check for loose or poor connections within generator control box 3) Check for loose or broken rotor securing stud.

REME M B E R ! IF IN DO U BT CONT A CT STEP H I L L GENER AT O R S LTD FOR FURTHER INF O R M A T I O N .

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