It gets a bit more complicated with HMIs because it not only matters what type of HMI ballast you use, but also what type of generator you use. If the OP were using incandescent lights, he could use a AVR type generator (AVR stands for Automatic Voltage Regulator.) However, the harmonic noise that a non-Power Factor Corrected (PFC) electronic HMI ballast will kick back into the power stream can have a severe adverse effect on the power waveform of conventional AVR generators like the Honda EX5500 (the “older EX 5.5 Silver” one Leonardo mentioned.) The harmonic noise these light sources generate will not have nearly as bad an effect on the power supplied by an inverter generator like the Honda EU6500is.
As the middle oscilloscope shot below indicates, when you power a standard non-PFC HMI Electronic ballast from a conventional portable generator, the harmonic noise they kick back into the power stream can have a severe adverse effect on the power waveform. Given the large sub-transient impedance of conventional portable generators, even a small degree of harmonic noise being fed back into the power stream will result in a large amount of distortion in its’ voltage.
Left: Grid Power w/ 1.2Kw Arri non-PFC Elec. Ballast. Center: Conventional AVR Power w/ 1.2Kw Arri non-PFC Elec. Ballast. Right: Inverter Power w/ 1.2Kw Arri non-PFC Elec. Ballast.
The adverse effects of the harmonic noise exhibited here, can take the form of overheating and failing equipment, circuit breaker trips, excessive current on the neutral wire, and instability of the generator’s voltage and frequency. Harmonic noise of this magnitude can also damage HD digital cinema production equipment, create ground loops, and possibly create radio frequency (RF) interference.
When your lighting package consists predominantly of non-linear light sources, like HMI, Fluorescent, & LED lights, it is essential to have Power Factor Correction circuitry (PFC) in the ballasts and to operate them on an inverter generator. The combination of improved power factor and the nearly pure power waveform (1-2 %THD) of a inverter generator creates clean stable set power (like that in the power waveform below right).
Left: Grid Power w/ 1.2Kw P-2-L PFC Elec. Ballast. Center: Conventional AVR Power w/ 1.2Kw P-2-L PFC Elec. Ballast. Right: Inverter Power w/ 1.2Kw P-2-L PFC Elec. Ballast.
Chris’s best bet would be to use a 1.2kw HMI with PFC ballast and use an inverter generator like the Honda EU6500is. The Honda EU6500is will also generate less than half the noise of an AVR type generator – making it easier to record clean audio tracks.
For more details on what type of generator to use with HMIs and fluorescent lights read the article I wrote for our company news letter on the use of portable generators in motion picture production. The article is available online at http://www.screenlightandgrip. com/html/emailnewsletter_generators.html.
Guy Holt, Gaffer, ScreenLight & Grip, Lightng & Grip Rental and Sales in Boston