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Core and Coil metal halide ballast
2013-12-18 08:34:15
Core and Coil ballast is the original type of ballast for a metal halide bulb, and for many years was the only option available. It remains the most common type, in part because it’s much cheaper to buy than electronic ballast. Depending on the wattage of bulb you’ll power with the Core and Coil metal halide ballast, expect at least a loss that will be around 10 percent of the lamp wattage, and can be much higher. You can buy magnetic ballast for metal halide lamps of up to 1500 watts.
The usual type of Core and Coil ballast sold for a metal halide bulb is called the constant-wattage autotransformer. It’s made up of magnetic coils and often includes a capacitor that offers improved power. It keeps the power to the bulb regulated so there’s little flicker. Also, if the line voltages varies a great deal, the ballast will prevent the bulb from shutting off.
Most Core and Coil ballasts used for metal halide lighting are the CWA (constant wattage autotransformer) type. This is a lead circuit ballast and consists of a high reactance autotransformer (core-coil) with a capacitor in series with the lamp. However, ballasts for 150-watt and 250-watt DE lamps tend to be the HX-HPF circuit type and require an igniter along with the capacitor and core-coil. Ballasts for pulse start lamps also have an additional igniter to start the arc, and have their own set of ballast circuit types.
Capacitors are needed to improve a ballast’s (input) power factor, and are integral components of CWA and regulated lag circuits; they will not operate without capacitors. Both oil-filled (wet) and dry-film capacitor technologies are commonly used with
magnetic ballasts. Oil-filled capacitors come in metal cases and are filled with a dielectric fluid; dry-film capacitors do not use a dielectric fluid. High intensity discharge lamp igniters provide a brief, high voltage pulse or pulse train to break down the gas between the electrodes of an arc lamp. Pulses can range from several hundred volts to 5kV. Typical durations are in the µsec range. They are usually timed to coincide with the peak of the open circuit voltage.
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