This type of ballast is used on Mercury Vapor lamps, Metal Halide lamps [typically 250-1000 watt] and Low Pressure Sodium lamps, where the line voltage is close to the required starting voltage of the lamp [typically for a line voltage of 240 VAC].
This is the most simple of the Ballasts, as it uses the basic components only - the Reactor core, which is the current limiting component.
** NOTE ** The Capacitor connected across the input is used to raise the Power Factor [PF] from nominal - or 50%, to High - or +90%.
This is also a simple Reactor core Ballast, which is used for High Pressure Sodium lamps, along with a few Metal Halide lamps where an Ignitor is incorporated in the circuitry to assist in starting the lamp after the lamp's arc drops out [typically from a voltage sag or momentary interruption in power]. MH Lamps can take upto 15 minutes to restrike after the arc dropped out, due to the high pressure created inside the arc tube from the high operating temperature.
The High Pressure Sodium lamp will usualy require the high voltage pulses from the Ignitor for starting under any conditions - cold startup or hot startup.
For 35, 50, 70, 100 and 150 watt 55 volt HPS lamps, this simple Ballast can be used where the input is 120 VAC. The 55 volt "S" lamps are the ones with the Medium Base screwshell.
They're arc tubes require at least 55 VAC to sustain the arc, once it has been established from the high voltage pulses of the Ignitor.
** NOTE ** When HPS lamps near the end of their operational usage [end of their lives], they will require an elevated level of voltage across the arc tube to keep the arc established. As they age, the required voltage becomes higher and higher, until the Reactor cannot supply the lamp with a high enough voltage. When this occurs, the arc [Plasma] shrinks rapidly, which results in the arc being extinguished. The high temperature of the arc tube creates high pressures inside the arc tube, so before the lamp can be "fired" again, the arc tube must cool down to a certain temperature - thus lowering the internal pressure. While this is taking place, the Ignitor is pulsing bursts of currents under aproximately 2,500 Volts of pressure through the arc tube. Pulses run on average 5 per second.
Once an arc has been created across the arc tube [in which a plasma is born], the lamp becomes the path of lower Impedance in the circuit, so the higher currents flow through the lamp - while minimal currents flow through the Ignitor.
I'll create a discussion thread for this ballast in the Theory section, then come back and insert a link here.
And here it is! Look in the Electrical Theory and Appications area for the subject heading of: Discussions On: HID Reactor Ballasts
Scott SET posted 07/21/2001
[This message has been edited by Scott35 (edited 07-22-2001).]