Working of Fluorescent Ballast

Fluorescent ballast is an electrical device intended to limit the amount of electric current in an electric circuit. This article elaborates on how it works and the procedure to test it.
The ballast or electrical ballast, as it is commonly known, is a device used for limiting the flow of charge in a circuit. It provides high voltage to initiate the current discharge. To sustain the discharge in a safe manner, the current is then limited quickly. They are used for lamps of three different types, i.e., rapid start, pre-heat, and instant start. This technology is also used in compact fluorescent lamps (CFLs).

How Does Fluorescent Ballast Work

This technology controls the flow of electrical discharge for pre-heat, instant start, and rapid start lamps, in the following manner.

Rapid Start Lamps
The rapid start lamp electrodes are heated before and during the electrical discharge. Transformers of this ballast possess two secondary windings. The low voltage needed by electrodes is provided by these secondary windings.

Pre-Heat Lamps
In these lamps, pre-heat operation lamp electrodes get heated prior to the initiation of electrical discharge. The flow of charge through all the electrodes is permitted by the closing of a starter switch. As the starter switch cools down, it gets opened, and voltage supply towards the arc tube is triggered. This whole process initiates the electrical discharge.

Instant Start Lamps
In these lamps, the instant start operation lamp electrodes don't get heated before the discharge. High voltage is provided by the ballast of instant start lamps in comparison to that of rapid start and pre-heat lamps.

How to Test Fluorescent Ballast
  • The electricity provided to the lamp should be turned off. The lamp should be removed from the fixture after it cools down.
  • The cover which is used for concealing the ballast should then be opened by taking off the screws.
  • If any leakage is observed, it should be removed because it could be damaged.
  • The high voltage side of the ballast should be checked for continuity between wires. The white colored wires are the neutral wires while yellow or blue are power wires.
  • The Volt Ohm meter should be turned to 'Ohms', followed by touching the two probes by their ends. A direct short or continuity is shown.
  • One of the probes of the ohmmeter should be touched with the white wire, and the other with either the yellow or blue wire. If a continuous or short circuit is not shown, then one can be sure that it is damaged. All the wires should be checked. If a short or continuous circuit is shown, then the low voltage side needs to be checked.
  • On the low voltage side, there are wires (black and white) which come from the ballast's power feed side. These wires should also be checked for continuous or short circuit. The low voltage side can be deemed as damaged if a short or continuous circuit is not shown.
Fluorescent Ballast Replacement
  • The lamp should first be removed and the light at the switch and circuit breaker turned off.
  • The screw that holds ballast to the fixture should then be removed.
  • A similar replacement ballast should be purchased from a hardware store. It should be attached to the fixture and the screws should be tightened.
  • The light should then be turned on at the circuit breaker as well as the switch. The new lamps should be replaced and the lights turned on.