Philips Electromagnetic Lamp manual 152, Fault finding

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3.19 Fault finding

If the mains current is about half the lamp current, the capacitor is in order, resulting in a power factor of approx. 0.9.

2)Disconnect capacitor from circuit and discharge by short-circuiting terminals.

Check capacitor with ohmmeter set at highest resistance scale. If the meter indicates a very low resistance which then gradually increases, the capacitor is in order.

If the meter indicates a very high resistance which does not diminish, the capacitor is open-circuit and should be replaced.

If the meter indicates a very low resistance which does not increase, the capacitor is short-circuited and should be replaced.

This method can also be used for the series capacitors.

Measurement of the starting pulse voltage of a starter is beyond the capability of most instruments available in the field, due to the high peak voltages.The practical way is to replace the suspect starter by another one.

Measurements on the ballast can be done in two steps after disconnecting the ballast from the circuit:

1)Check with ohmmeter on the terminals.Values should be low (15 to 200 Ω , depending on lamp power). If the value is high, the ballast is

open-circuit.

2)Connect ballast on the mains supply (well fused!) and measure the short-circuit current.This should be approx. 1.5 times the nominal lamp current.

Measurements of the lamp electrodes can be done at the 4-pin versions with a standard ohmmeter.The resistance of the electrodes varies for the different lamp types, but is less than 50 Ω when cooled down.

Measurements on the lamp in operation can only be done if the starter is not operative.As the lamp voltage is not a sine wave and subject to the tolerances in the total circuit, measured lamp voltages only give a rough indication of correct functioning.The lamp current can be measured rather accurately.

Measurements of the mains supply normally involve the effective value of the supply voltage and mains current and sometimes the frequency. When pulses, interruptions, harmonics (wave form) can play a role, ‘laboratory’ instruments are necessary, preferably during a longer period while storing or noting the readings.

It is advisable to measure the various phase currents in an installation, in order to check the balance of the load.Also the measurement of the current in the neutral in a star network gives an indication of the quality of the total system. Due to harmonics in the lamp current, the current in the neutral is not zero, but should be 50....70 per cent of

the phase currents. If the current in the neutral is higher than in the phases, the balance in the load is not correct or the mains supply waveform does not have a good sine wave.This can lead to overload of the neutral cable.

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