Electric Ballast_Siddharth Chauhan

8/9/2019 Electric Ballast_Siddharth Chauhan

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A device required by electric-discharge lightsources such as fluorescent or HID lamps toregulate voltage and current supplied to thelamp at the start and throughout theoperation.

Ballasts vary greatly in complexity. They canbe as simple as a series resistor as commonlyused with small neon lamps.

For higher-power installations, too muchenergy would be wasted in a resistive ballast,

so alternatives are used that depend upon thereactance of inductors, capacitors, or both.Finally, ballasts can be as complex as thecomputerized, remote-controlled electronicballasts used with fluorescent lamps.


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Why an Electronic Ballast isNeeded

A lighting ballast is necessary to operate discharge lightsbecause they have negative resistance.

The discharge light sources are unable to regulate the

amount of current that passes through them.

A lighting ballast must be used to control current flow;otherwise the light source could fail .


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Electronic Lamp Ballast...

Uses solid state electronic circuitry to provide the properstarting and operating electrical condition to power one ormore fluorescent lamps and more recently HID lamps.

Usually change the frequency of the power from thestandard mains (e.g, 50Hz in India) frequency to 20,000 Hzor higher, substantially eliminating the Stroboscopic

Effectu of flicker (100 or 120 Hz, twice the line frequency)associated with fluorescent lighting . The lamps actually operate at about 9% higher efficacy

above approximately 10 kHz


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Because of the high frequency of operation, electronicballasts are generally smaller, lighter, and moreefficient (and thus run cooler) than line frequencymagnetic ballasts

Electronic ballasts are often based on the SMPStopology, first rectifying the input power and thenchopping it at a high frequency. Advanced electronicballasts may allow dimming via pulse-widthmodulation


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Why all the Hype aboutElectronic Ballasts?

Higher light output than electromagnetic ballastsat the same power input level .

Electronic ballast manufacturers have developeda variety of ballast types for the various availablelamps .

The familiar hum of electromagnetic ballastshas all but been eliminated .

Color rendering has improved . Lamp flicker has been greatly reduced .

Further energy savings can be realized byreducing the heating load on the system.


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How Do Bulbs Work? The modern light bulb,

which hasn't changeddrastically sinceEdison's model, ismade up of only ahandful of parts.

Light is a form ofenergy that can bereleased by an atom. Itis made up of manysmall particle-likepackets that haveenergy and momentumbut no mass. Calledphotons.


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At the base, they have twometal contacts

The metal contacts areattached to two stiff wires,attached to a thin metalfilament

The filament sits in themiddle of the bulb, held upby a glass mount.

The wires and the filamentare housed in a glass bulb,which is filled with an inert

gas, such as Argon.


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The bulb is hooked up to a power supply An electric current flows from one contact to the other As the electrons zip along through the filament, they

are constantly bumping into the atoms that make upthe filament.

The energy of each impact vibrates an atom -- in otherwords, the current heats the atoms up.

Bound electrons in the vibrating atoms may beboosted temporarily to a higher energy level. Whenthey fall back to their normal levels, the electronsrelease the extra energy in the form of photons.

The filament in a light bulb is made of a long,incredibly thin length of tungsten metal.


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Necessity For CurrentLimiting

Ballasts are most commonly needed when anelectrical circuit or device presents a negative(differential) resistance to the supply.

If such a device were connected to a constant-voltagepower supply, it would draw an ever-increasingamount of current until it was destroyed or caused thepower supply to fail. To prevent this, a ballast providesa positive resistance or reactance that limits theultimate flow of current to an appropriate level. In thisway, the 'ballast' provides for the proper operation ofthe negative resistance device.

Examples of such negative-resistance devices are gasdischarge tubes and lamps.


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Starting of an ElectronicBallast

Electronic Ballasts use threemethods of starting:

instant start, rapid start, andprogrammed start. The firsttwo methods also are

available in electromagneticballasts, while the last one isoffered only by electronicballasts.

Playing with an Electronic Ballast


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Instant start provides the most energy-efficientoperation for T8 lamps and should be used inapplications where the lamps will operate more thanthree hours per start.

Rapid start ballasts are intended to prolong

lamp life, with a 15% to 25% increase in switch cyclesbefore failure, depending on individual ballast design.

Programmed start ballasts are best suitedfor applications where the lamps will operate less thanthree hours per start and offer an increase in switch

cycles before failure of 100% or more over the rapidstart ballasts.


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Electro-Magnetic Ballast Electromagnetic ballasts limit the flow of

current to the light but do not change thefrequency of the input power. The lampthen illuminates on each half-cycle of thepower source. This is why manyfluorescent and neon lights visibly flicker.

Since the light illuminates on half-cycles,the rate of flicker is twice the frequency ofthe power source, meaning the light willflicker at 100Hz or 120Hz. A lead-laglighting ballast can minimize flicker whenconnected to two lamps by alternating the

flow of current to them: one leading thefrequency of the input power and the otherlagging behind it.


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MAGNETIC ELECTRONICCore & Coil Electronic,

microprocessor

Rated Lamp Life20,000 hours

Rated Lamp Life20,000 hours

Mean Calculated @40% of rated lamplife8,000 hours

Mean Calculated @40% of rated lamplife8,000 hours

Lumen Maintenance(Output @ Mean)64% of initiallumens

Lumen Maintenance(Output @ Mean)86% of initiallumens

Mean Lumens

Good lighting systems are

specified on the basis of mean

or average light output of the

lamp. This mean is defined as

the light output, measured in

lumens, at 40% of the lamps

rated life.

Cost of Ownership - Long

Term Savings*

While the initial cost of a

magnetic ballast is considerablyless than a high performance

electronic ballast, the over-all

cost of ownership is much

higher.

Comparing Electronic andElectromagnetic Ballasts


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MAGNETIC ELECTRONIC

Installing more fixtures means...

Higher installation laborHigher material costsHigher energy costs

Install up to 36% fewer FUTURE

BRITESAchieve the same light levelsLower cost of ownership


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Few Examples.

HPF ELECTRONIC BALLAST


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Self-Oscillating Dimmable Electronic Ballast


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FAQ:- Flicker And Stroboscopic Effect The mercury arc in a fluorescent

lamp operated on a 60 hertzalternating current goes on and off120 times per second. The light fromthe lamp would go out completely

except that the phosphors havesome phosphorescent or "carry-over"action. That is, they continue to glowfor a short time after the existingradiation is cut off.

This variation in light output is

known as flicker. The flicker rate overthe length of the lamp is 120 cyclesper second. At the ends of the lamp,each alternate flash is comparativelyweak. This gives an effective rate of60 flashes per second.


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The 120-cycle flicker is too fast to be visible. The 60-cycle flicker can be detected, but only by theperiphery of the retina. For this reason, lamp flicker isseldom noticed except when observing the ends of thelamps out of the corner of the eyes or related

equipment.


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Electric Ballast_Siddharth Chauhan

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