...... I'm wondering what is going on inside the ballast and whether the ballast itself will be power limited in some way.
Kino fluorescent ballasts are a Switch-mode Power Supply (SMPS) designed to perform all the same functions as a magnetic fluorescent ballast but at a higher frequency. They first rectify the 60 Hz AC input to DC and then produce a very high frequency alternating current (20,000 - 50,000 Hz depending on the fixture) from the DC using an inverter and power conditioning components.
The high frequencies at which Kino ballasts operate is what makes them a suitable light source for film and television production. By converting the 60 Hz input frequency to between 20,000 - 50,000 Hz, Kino ballasts eliminate the problem of light intensity fluctuation associated with standard magnetic ballasts. At those frequencies the period of time between the off and on pulse of each cycle is so short that the illuminating phosphors do not decay in light output.
Like the glowing tungsten coil of an incandescent lamp, the fluorescent phosphors become essentially flicker free. Electronic fluorescent ballasts also weigh less and don’t have the characteristic hum of magnetic ballasts. These characteristics of the Kino Flo high frequency electronic ballasts make them well suited for motion picture lighting.
Schematic of typical of electronic ballast: L-to-R consists of half-bridge rectifier, conditioning capacitor, DC/AC Inverter.
All Kino ballasts utilize a Diode-Capacitor circuit on the front end (to the left of the dashed line in the schematic above) to first convert the AC line input to DC. A pair of MOSFETS (to the right of the dashed line in the schematic above) act as a high frequency DC to AC inverter to create the high frequency alternating current (20,000 - 50,000 Hz depending on the fixture) that drives the fluorescent tubes.
So that they can operate off of a car battery, the 9” Kinos separate these two stages in separate boxes - the MOSFETS in one and the Diode-Capacitor circuit in another. This way 12V DC from a car battery can be fed directly to the MOSFETS to invert to high frequency alternating current. To operate them on wall outlets, there is a separate box that contains the Diode-Capacitor circuit that converts the 60Hz AC to 12V DC.
Unless power factor corrected the Diode-Capacitor circuit of an electronic ballast generates a high level of capacitive reactance, which leads to an inefficient use of power and the generation of harmonic currents (use this link more detailed information about how Fluorescent ballasts, as well as HMI & LED ballasts, operate.)
Guy Holt, Gaffer
ScreenLight & Grip
Lighting Rental & Sales in Boston