Lighten Up: Doing More with Less without Compromise
Written by Guy Holt | Posted by: NewEnglandFilm.com
A new generation of smaller & brighter lights that consume less power have resulted in new and more cost effective lighting techniques. To this, add the greater light sensitivity and contrast range of HD camera systems and it is possible to shoot an entire feature production with what can be powered by a portable generator. Unfortunately, sizing a portable generator for a lighting load can be very complicated. When you use lights sources like HMIs, Kinos, CLF lamp banks, & even LEDs, on generators it matters not only what type of generator you use but also what type of ballasts the lights use. That is because the poor Power Factor and Harmonic Noise that magnetic and non-Power Factor Corrected electronic ballasts (HMI, Kino, CFL, & LED) kick back into the power stream can have a severe adverse effect on the power waveform of some generators, but not others.
For example, what size generator is required to power a small lighting package consisting of a 800W Joker Buglite and two 40W 1×1 Litepanels? You would think that you could operate this lighting package on a conventional 1000W generator (800W+40W+40W= 880W.) However, when your lighting package consists predominantly HMIs, Kinos, CLF lamp banks, & even LEDs, you must consider the Power Factor of the lights when calculating the load that you will put on the generator. A careful analysis of the Power Factor of the Joker 800 and 1×1 Litepanel indicates that our lighting package would in fact overload a conventional 1000W generator.
If we look at the technical specifications for the Joker 800 Buglite, we see that it uses a non-Power Factor Corrected ballast with a Power Factor of .58. According to the K5600 website, the Joker 800 ballast draws 12.5 Amps rather than the 7 Amps you would think using Ohm’s Law (800W/110V=7.2A.) What that means is that it has an Apparent Power of 1375W (110V x 12.5A = 1375W) or draws nearly twice the power to generate 800W of light output than a quartz instrument of the same wattage. Used on wall outlets, this relatively inefficient use of power is negligible because the power draw of the Joker 800 fits easily in a standard wall circuit. However, the greater Apparent Power of the Joker 800 must be factored when using portable generators because the generator must be sized to supply the Apparent Power (1375W), even though only the True Power (800W) provides light.
The same is true when it comes to the 1×1 Litepanels. According to the manufacturer, the AC-to-DC power supply that Litepanel uses for their 1×1 fixtures has a Power Factor of .54 and so draws nearly twice the power (an Apparent Power of 75W) for it’s true power output of 40W. If you were to use this lighting package on a 1000W conventional generator, the total Apparent Power of 1525W (1375W + 75W + 75W = 1525W), would overload the generator because the ‘continuous load’ rating of 1000W conventional generators are usually only 850W. Even though it’s power is cleaner and more stable, you would not be able to run this package on a Honda EU1000is Inverter Generator either because, with a continuous load rating of 900W, the accumulative load of 1525W would also overload a 1000W inverter generator.
Could you operate this lighting package on a 2000W conventional generator? Again, the answer is ‘no’ because the greater Apparent Power of lights with a poor Power Factor is not the only consideration when operating them on conventional generators. Of equal importance, is the Harmonic Noise that ballasts with poor Power Factor kick back into the power stream that severely limits the total amount of Leading Power Factor loads, as compared to Unity Power Factor loads, that can be reliably operated on conventional generators.
Given the large sub-transient impedance of conventional 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. Add to that, the fact that the original supply voltage waveform of conventional generators is appreciably distorted to begin with, and you have a situation where the return of any harmonic currents by a non-PFC HMI, Fluorescent, or LED ballast will result in significant waveform distortion of the voltage at the power bus and operational problems with the generator voltage and frequency regulation.
This is graphically illustrated in the You-Tube video, ‘Compact Fluorescent verses The Generator’, by Lighting Designer Kevan Shaw’s (available on-line here), when he is not able to operate an equivalent Apparent Power of CFLs, as he could incandescent light, on his small 850W generator.
In fact, Kevan Shaw’s You-Tube video illustrates the general rule of thumb that it is not possible to load conventional generators beyond roughly 65% of their rated capacity for more than a short period when the load consists of lights with a poor Leading Power Factor ( Max Apparent Power of 540W/850W Generator = .64) Which translates to a maximum load of 1300W on a 2000W conventional generator. Where the total Apparent Power of our lighting package consisting of a Joker 800 and a couple of 40W 1×1 Litepanels is 1525W, it will overload even a 2000W conventional generator.
Will our lighting package operate on a 2000W inverter generator like the Honda EU2000is? The oscilloscope shots above indicate that it would. Even though the non-PFC ballasts of our lighting package kick back the same harmonic currents, the voltage waveform of inverter generators retain an over all sinusoidal shape because of their lower system impedance and purer original power waveform. The appreciable difference in voltage distortion created here by the same light demonstrates that an inverter generator will provide cleaner power, and operate more reliably, regardless of the type of load.
Power Factor Correction can be of tremendous benefit when operating HMIs, Kinos, and LEDs on portable gas generators because a PFC circuit realigns voltage and current, eliminates the generation of harmonic currents, and induces a smoother power waveform at the distribution bus. PFC circuits successfully increase the power factor to as much as .98, making ballasts with it near linear loads. As a result, the ballast uses power more efficiently with minimized return current and line noise and also reduces heat, thereby increasing their reliability. For instance, if you were to replace the Joker Ballast with a Power-2-Light 800W PFC HMI ballast instead, the same head would draw 8 Amps at 110 Volts (instead of 12.5) and have an Apparent Power of only 880 Watts. If you were also able to replace the non-PFC AC power supplies of the 1×1 Litepanels with Power Factor Corrected ones, the oscilloscope shots above also indicate that you would likely be able to operate the whole package on a 1000W inverter generator (880W + 40W + 40W = 960W.)
A modified Honda EU6500is with our Transformer/Distro can power the PFC 2.5 & 1.8 HMI Pars, PFC 400w Lighthouse HMI, 2 ParaBeam 400, 2 ParaBeam 200s, and 2 Tegra 400s of our HD P&P Pkg.
What is true of small lighting loads on small generators, is also true of larger lighting loads on larger generators. For instance, before reading this article, you would have thought that you could reliably operate a 4k HMI with non-PFC ballast on a conventional 6500W generator. But, where a non-PFC 4k electronic ballast will draw 58A at 120V it will overload a 6500W. To understand why, simply compare its’ Apparent Power of 6960W (58A x 120V = 6960W), to the continuous load capacity of a conventional 6500W generator after de-rating it for a load with Leading Power Factor of .58 (6500W x .65 = 4225W.) Likewise, if you were to replace the non-PFC 4k electronic ballast with a Power Factor Corrected one, the light would only draw 38A at 120V and have an Apparent Power of 4560W. And since, the ballast has a near Unity Power Factor, the 6500W generator would not have to be de-rated, and so could operate the 4560W Apparent Power load without a problem.
How to Learn More
The poor Power Factor of HMIs, Kinos, CLF lamp banks, and even LEDs, have been vexing set electricians for years. For more insight into operating bigger, or more small, lights on portable generators than has ever been possible before, join author Guy Holt on Feb. 16th, 2013, for a workshop on new trends in production titled ‘Lighten Up: Doing More with Less without Compromise.’ As part of the same Boston workshop series, New England Studios, Talamas Broadcast, and Production Hub will be sponsoring a workshop on ‘Video Lighting Design’ by L.D. Richard Cadena. Noted Focal Press Author, ETCP Trainer, and Founder of the Academy of Production Technology, Richard’s workshops are both lively and informative. Log onto bit.ly/nptwkshps for more workshop information and registration details.
For more information on the Feb 9 workshop with Richard Cadena, please click here. For more information on the Feb 16 workshop with Guy Holt, please click here.