Electrical ballast

To allow the engine to start, the ignition system was designed to operate on this lower voltage.

But once the vehicle was started and the starter disengaged, the normal operating voltage was too high for the ignition system.

Another common use of a ballast resistor in the automotive industry is adjusting the ventilation fan speed.

A very common failure occurs when the fan is being constantly run at the next-to-full speed setting (usually 3 out of 4).

This will cause a very short piece of resistor coil to be operated with a relatively high current (up to 10 A), eventually burning it out.

These devices are sometimes called "barretters" and were used in the series heating circuits of 1930s to 1960s AC/DC radio and TV home receivers.

[citation needed] This property can lead to more precise current control than merely choosing an appropriate fixed resistor.

A commonly used light in the home in the 1960s in 220–240 V countries was a circular tube ballasted by an under-run regular mains filament lamp.

An electronic ballast is usually quieter than a magnetic one, which produces a line-frequency hum by vibration of the core laminations.

Advanced electronic ballasts may allow dimming via pulse-width modulation or via changing the frequency to a higher value.

Systems with remote control of light level via a wireless mesh network have been introduced.

The high output frequency of an electronic ballast refreshes the phosphors in a fluorescent lamp so rapidly that there is no perceptible flicker.

[6] Because more gas remains ionized in the arc stream, the lamp operates at about 9% higher efficacy above approximately 10 kHz.

[6] This technique uses a combination filament–cathode at each end of the lamp in conjunction with a mechanical or automatic (bi-metallic or electronic) switch that initially connect the filaments in series with the ballast to preheat them.

This system is described as "Preheat" in North America and "Switch Start" in the UK, and has no specific description in the rest of the world.

DC fittings were complicated by the need to reverse the polarity of the supply to the tube each time it started.

An instant start ballast does not preheat the electrodes, instead using a relatively high voltage (~600 V) to initiate the discharge arc.

It is the most energy efficient type, but yields the fewest lamp-start cycles, as material is blasted from the surface of the cold electrodes each time the lamp is turned on.

Instant-start ballasts are best suited to applications with long duty cycles, where the lamps are not frequently turned on and off.

A resistor of about 10 kΩ is required to be connected in parallel with the fluorescent tube to allow reliable firing of the quadrac at low light levels.

An electronic ballast with an integrated rechargeable battery is designed to provide emergency egress lighting in the event of a power failure.

When power is lost, the ballast will illuminate one or more lamps in the fixture at a reduced output for a minimum of 90 minutes (as required by code).

An American electronic instant start ballast for powering a variety of American T8 fluorescent lamps .
Variety of ballasts for fluorescent and other discharge lamps
A typical 230V, 50hz series choke ballast (inductor) used in older lighting. This example is used for a tanning lamp . It requires a starter switch (below).
A lamp starter , required with some inductor type ballasts. It connects the two ends of the lamp to preheat them for one second before lighting.
A fluorescent lamp , a device with negative differential resistance. [ 1 ] [ 2 ] In operation, an increase in current through the fluorescent tube causes a drop in voltage across it. If the tube were connected directly to the power line, the falling tube voltage would cause more and more current to flow, until it destroyed itself. [ 1 ] [ 3 ] To prevent this, fluorescent tubes are connected to the power line through a ballast . The ballast adds positive impedance (AC resistance) to the circuit to counteract the negative resistance of the tube, limiting the current. [ 1 ]
Several American magnetic ballasts for fluorescent lamps . The top is a rapid start series autoregulator ballast for two 30–40 W lamps. The middle is a preheat reactor ballast for a single 30–40 W lamp while the bottom ballast is a simple inductor used with a 15 W preheat lamp.
An American magnetic ballast for signs in an aluminum sign frame. Ballasts for sign lighting in the United States, are heavier duty than other ballasts because the cooler outdoor temperatures increase the energy required to start a fluorescent tube. They are sized based on the total tube length used.
Typical European 230V series choke ballast 40W T12 or 36W T8 fluorescent lamps .
Electronic ballast of a compact fluorescent lamp