Factors that Affect Specification of A Ballast

The following factors affect ballast specifications:

a) Lamp wattage regulation spread (expressed as a %): To arrive at the lamp wattage regulation spread, divide the difference between the maximum watts and minimum watts by the nominal or design watts; then multiply by 100. As an example, a nominal 400 watt H.P.S. lamp is rated at 100V, and the ballast is designed to operate a nominal 100V lamp at rated watts. The nominal watts in this example equals the design point at 400 watts. The same nominal 100 volt lamp with 10% more line voltage from the ballast measuring 435 watts is the maximum watts; with 10% less line voltage is the minimum watts, measuring 365 watts. The regulation spread then, using the formula detailed above, is 70 divided by 400, times 100 or 17.5 percent for a 400 watt H.P.S./C.W.I. type ballast. A safe spread for ballasts with lamps less than 400 watts is 18 percent. Note: H.P.S. regulation is a total percent spread and not a plus or minus variation. When the 400 watt H.P.S. lamp reaches 130 volts, the spread is 31 percent.

b) Lamp current crest factor: This is the ratio of the peak current to the average current. To ensure rated lamp life and lumen maintenance, manufacturers specify a maximum limit. Anything above this can shorten the lamp electrode life. Ballasts with a 1.8 crest factor or less will provide rated lamp life performance. Venture now offers newly-engineered ballasts with reduced current crest factor for use with Uni-Form pulse start lamps. The improved crest factor design yields additional benefits over traditional ballast designs due to less stress on the electrodes from the higher current.

These low crest factor ballasts work with high voltage pulse ignitors to allow quicker cold starting and faster hot restarts, a proven factor in longer lamp life and superior lumen maintenance. The new designs all offer lower current crest factor, as low as 1.4.

c) Ballast power factor: A regulating ballast design compensates for line voltage range, and a non-regulating design does not compensate. Common names for non-regulating types are reactor, lag, and autotransformer/reactor. Common names for regulating types are: regulator, constant wattage (CW), constant wattage isolated (CWI), and constant wattage autotransformer (CWA). All regulating types are HPF with the capacitor in series with the lamp. Non-regulator ballasts can be either normal power factor (NPF) or high power factor (HPF). HPF has a capacitor across the line.

d) Lamp failure modes: All. lamps will eventually fail and ballasts must be designed with that fact in mind. Lamps which need to be replaced usually cycle on and off, although they may also fail in a short circuit mode as a result of mechanical failure. The ballast must be designed for the following operating modes: start, warm-up, and proper burning operation; failure due to open circuit cycling; and mechanical failure due to open or short circuit.

e) Ballast/starting aid compatibility: Venture designs and controls the components of all starting aid systems. When used as designed, a ballast and starting aid will operate under open circuit conditions without an appreciable loss of life for three months.

f) Ambient and operating temperature rating: The life of any ballast is directly affected by heat. The introduction of smaller lighting fixtures, ballast housings, and ballasts has resulted in higher operating temperatures. Insulation systems that have been designed for specific operating temperatures will last for an average of approximately 60,000 hours. But if a ballast is operated at 10°C over the design temperature, its operating life will be decreased by approximately 50 percent. Temperature ratings for ballasts take into account the temperature of the surrounding air where the ballast is placed (ambient), and the operating temperature which includes the heat generated by the lamp and the ballast. The following is a typical profile:

Normal rated ambient temperature 40°C

Typical average ballast temperature rise 90°C

Typical fixture temperature rise (lamp heat) 15°C

Total operating temperature of insulation system 145°C

All Venture core and coil ballasts are manufactured to Class H standards. The total operating temperature of 145°C is safely below the ANSI standard maximum limit of 165°C, and will give the system normal H.I.D. ballast life.

NOTE: The fixture temperature rise may vary substantially depending on the fixture design, lamp rating, and operating conditions. The total operating temperature should not exceed the ANSI standard maximum limit of 165°C.

Recommended maximum ambient temperatures are listed below.

Venture manufactures a line of specially designed ballasts for operation in maximum ambient temperatures of 60°C (140°F). Design features of this line include superior insulation, high temperature potting compound, and specially designed capacitor enclosures. These ballasts are recommended for use in areas where high ambient temperatures prevail.

The advice of a Venture technical specialist should be sought whenever the installation of ballasts in abnormal conditions is required. One proven method to combat conditions such as a corrosive atmosphere, high ambient temperatures, or excessive humidity, is to mount the ballast in a remote location.

g) Fixture/Ballast Housing design: The mounting of core and coil ballasts within the enclosure of a lighting fixture or ballast housing is critical to its operation. Heat dissipation leading to premature ballast failure and can be prevented by a core and coil ballast. It is therefore necessary to install the core and coil ballast in a way that conduction and radiation take place to dissipate the heat generated.