Mercury Vapor Ballasts
Mercury vapor ballasts are designed to drive tubular medium pressure ultraviolet lamps. There are two types of mercury vapor lamps.The most common is the medium pressure lamp with no metal additives. This lamp is available in arc lengths of 1 to 120 inches.The other type of lamp is a metal-additive-mercury-vapor lamp. The additives used in the lamp create changes in the lamps spectral output enhancing different portions of the ultraviolet spectrum.The ballast initiates and controls the arc in mercury and metal additive curing lamp. This is accomplished by providing an instantaneous high voltage to strike the elements within a mercury vapor lamp, creating a plasma that, once initiated,is sustained by the ballast.Total wattages up to 50 kilowatts can be designed.Our constant wattage ballast consists of a transformer,capacitors and igniter.
The advantage of a constant-wattage ballast is that it allows for wide variations in input voltage to affect output wattage by only a few percent. These ranges can be customized to meet your applications requirements. Typical designs have an output variation of only +/- 3% with an input voltage varying over a range of -15% to +10%. Constant wattage is accomplished by a resonant tank circuit in which the lamp winding is in controlled magnetic saturation with the AC capacitors, such that voltage swings on the input side have a very small impact on lamp current. An interesting feature is that these current-limiting capacitors can be switched (see schematic) in and out of the circuit to provide various lamp power levels.
Metal Additive Ballasts
Metal additive ballast is required for metal additive lamps. In addition to needing a higher open circuit voltage a metal-additive lamp requires a special wave-shape to main the arc plasma. The metals inside the lamp create electrical noise in the ballast secondary circuit, which normally would cause the lamp to extinguish during lamp warm-up, if a standard ballast were used. The metal additive ballast uses a special bridge gap design to successfully shape the waveform and absorb this noise.
From the user standpoint the metal-additive ballast has the same schematic as the mercury ballast. And can be used to operate a mercury lamp, but a mercury lamp ballast can not be used for an additive lamp.
Ballasts are available in sizes from 400 watts to 50kW in 50, 60, or 50/60Hz. Typically, input power factor is better than ninety (90%) percent at nominal input voltage. Ballasts are constructed using silicon grain oriented steel, UL rated copper wire, UL Class H insulation system and impregnated with a unique epoxy varnish for maximum thermal transfer.
Controlled Ferroresonant Ballast
The controlled- ballast offers a linear variation of output power from 40 to 100%. A standard ballast switches capacitors in and out of the circuit to change lamp power as a step function.With a Controlled-Ballast, lamp power is adjusted by varying the conduction time on an inductor, which negates capacitance in the circuit allowing enhanced control of lamp current. Lamp current is sensed in a closed feedback loop circuit that can instantaneously respond to changes making the necessary adjustments.
Another advantage is that since the controls are on the secondary of the ballast all the electronics are protected from power problems found on the primary side. A PLC interface is available to communicate with the ballast in order to vary lamp output. In order to protect all of the control circuitry from power problems typically found on the primary the control circuits are all located on the secondary of the ballast.
- Continuously variable output power from 40% power through 100% power
- Precise regulation, less than a 2% change in output power over an input range of +l0% to - 20%
- Low input current distortion seen on SCR controlled designs.
- No need for mercury relays.
- Very high input power factor. Typically better than 0.90
- Low lamp current crest factor, 1.5 typical
- High watt efficiency
- Controllable via a Programmable Logic Controller (PLC). A 4ma to 2Oma signal is preferred with 0 to 5 volt or 0 to 10 volt option.
- All components are pre-wired and tested at the factory
- Easy to wire. Just six wire connections need to be made to make the system operational
- Capable of running either a standard mercury lamp or metal halide lamps
- Secondary wave-forms are designed to improve lamp life
If your application requires an accurate variation of lamp output power over a range of 30% power to full power, saturable reactors are available to provide a smooth, linear variation of lamp power.