Powering HMIs & Kinos with batteries for Night Shoot

[Isabelle Landers]

I am shooting a night scene on a back country road. We can't afford a movie blimped tow generator and I am afraid a portable generator will be too loud. What are my options for powering HMIs and Kinos on batteries. I have looked at a number of different types of Inverters - from boat inverters to Dewalt construction inverters - but don't know which is right or what they can handle. Any tips would be greatly appreciated.

- Isabelle Landers,

[Pietro Impagliazzo]

If you stick to tight shots with no need to light huge backgrounds areas LEDs could be a way of lighting it, just run them off batteries.

HMIs would be more tricky because of their wattage though.

Since you didn't mention LEDs seems like you're using available gear and renting or getting it somehow is not an option?

Anyone with Gaffer skills could chime in?

And welcome to the forums Isabelle. A female DP? We had a thread (http://www.scarletuser.com/showthread.php?t=200) about this. :)

[Granty]

Sounds like a back country road is going to need some heavy lighting at night. Not too sure on battery optiions but I know they ain't cheap.

You can get some quieter generators around, and if you throw it behind some trees on a long extension behind camera and sound, it may just work for you, even if you box it in and then get that mic in close on the action.

Only other options are creative tricks really, day for night is perfect for a back country road, or creative edit and over-dub to get rid of background noise, I always had to do sound after the take then shooting indoor with a old 16mm camera.

The last option depending on footage needs and timings is wait to hire a Canon 1D mark 4, if you have a fast lens, a full moon and maybe a bounce board I think you will get some perfect natural lighting.

[Pietro Impagliazzo]

I had no idea the 1DMk4 was such a night vision device, well, I thought that was just a figure of speech.

[Granty]

Open moon light is about .1 foot candle and the 1D Mk IV's expanded ISO of 102400 is 4 2/3 stops faster than ASA/EI 3200. Using the ASC charts as a guide, with a T Stop of 1.4 if my math is correct (4 2/3 stops faster than 1 is .048) that should be enough light to actually expose, albeit a noisy exposure no doubt, in available moon light. Has anyone out there had the opportunity to try this camera out in only available night time "light"?
So if you rent that camera with a 50mm 1.2 lens, add a bit of bounce light you can drop that ISO a few notches and still expose.

If the human eye can see it, that camera can - and then some.

[Isabelle Landers]

If you stick to tight shots with no need to light huge backgrounds areas LEDs could be a way of lighting it, just run them off batteries. HMIs would be more tricky because of their wattage though. Since you didn't mention LEDs seems like you're using available gear and renting or getting it somehow is not an option?


I don't have access to a Canon 1D mark 4 or LED Lights. I do have to lights the background in wide shots because a charater has to be seen moving in the woods along side the road. In my experience LEDs don't have that kind of punch. Day-for-night is not an option because the car lights figure heavily into the lighting design and they do not read on day-for-night. We tried shooting some test footage with a Honda ES6500 and found that no matter where we put the generator we still heard it. Which brings me back to either renting a movie blimped tow genertor (not in the budget) or using inverters on batteries. I think I can get by with a 1200 Par HMI (a 2500 would be better) and the headlights for the background and a couple 4' 4 Bank Kinos for talent keys around the car. I would go with smaller Kinos but their light drops off so quickly that I found on the test shoot that only a 4' 4 bank gave us the level we needed. The largest True Sine Wave inverter I have found is an 1800W with a load capacity of 15amps. The problem is that all the 1200 Par Electronic ballasts I have looked at draw 18-19 Amps which is too much for the inverter and the car lighter socket. And I still need power for the Kinos. I have found larger modified square wave inverters but don't know if the HMI or Kinos will work on them. Any help would be greatly appreciated.

- Isabelle Landers

[Pietro Impagliazzo]

So it looks like you really need gaffer help.

If you're unhappily willing to use a 1200W PAR sounds like an even lower wattage light would not be suitable?

Isabelle, did you try posting on REDUser? Post on the cinematography area there and you should get great feedback no doubt.

http://www.reduser.net/forum/forumdisplay.php?f=28

It also remembered me of a David Mullen's post where he talks about a Coen brothers film where the DP (probably Roger Deakins) could not light the whole road and decided to shoot the pursuit scene lit with only the cars headlights.

Do you think a 1200W PAR on the BG would make that much of a difference?

Are there trees in the BG? Maybe you can rig some battery powered work lights some feet apart and up in the trees or in poles to simulate street lights? And just use the Kinos and healights for the actors.

Just thinking outloud.

Edit: I see you posted on REDUser.

[Granty]

It also remembered me of a David Mullen's post where he talks about a Coen brothers film where the DP (probably Roger Deakins) could not light the whole road and decided to shoot the pursuit scene lit with only the cars headlights.


Also reminds me about The Wrestler, inside the bar (strip club) they usied a few lights but moved the rig with the camera. So if you frame it right you can move the lights along with the camera, or have the camera and lights on the same rig. Won't be good for looking up and down the road, but for close and mid shots with the trees just behind will be fine.

You can do 'day for night' with car lights in twilight, or do some tracking cgi to add those headlights.

http://www.videocopilot.net/tutorial/day_to_night_conversion/

This above link isn't the best After Effects comp I've seen done, but may give you some creative ideas.

[Isabelle Landers]

Isabelle, did you try posting on REDUser? Post on the cinematography area there and you should get great feedback no doubt. http://www.reduser.net/forum/forumdisplay.php?f=28... Do you think a 1200W PAR on the BG would make that much of a difference?

Are there trees in the BG? Maybe you can rig some battery powered work lights some feet apart and up in the trees or in poles to simulate street lights? And just use the Kinos and healights for the actors.

Yes, I posted on Red User without much luck so far. As I mentioned on Red User, we had originally planned for an 18k but the project funding did not come through, and we are pushing ahead with what we can afford. We had originally planned to rent a tow generator, but now can't afford the additional costs involved in towing it. Since Ryder, Budget, U-Haul, and Penske don't equip their trucks to tow we have no alternative but to get the rental house to tow it on one of their grip trucks. So rather than renting a box truck and shelving it out, we have to rent the rental house grip truck. And instead of driving the truck myself, we have to hire the company grip/driver to drive the truck for insurance reasons. At the day rate they want, the grip/driver would be the highest paid member of the crew. Where the cost of renting a movie tow plant is much more than just the cost of the generator we are forced to scale down.

The script calls for a specific back country road where there would not be streetlights. I realize a 1200 Par is not going to go far so I had planned to use the car headlights to work the background as well. A 2500 Par would be better but I don't see how we can power it. I don't see how we can power a 1200. Moving to a location with a power drop is unfortunately not an option because the whole reason we are shooting there is a natural rock formation that is part of the story.

- Isabelle Landers

[nejuicer]

I realize a 1200 Par is not going to go far so I had planned to use the car headlights to work the background as well. A 2500 Par would be better but I don't see how we can power it. I don't see how we can power a 1200.

There is a way to do everything you want including the 2500 Par. First, you will be able to run a 1200 Par along with a couple of Kinos on a "True Sine Wave" 1800W inverter if the ballasts (both HMI & Kinos) are Power Factor corrected. Not just any inverter will do when powering fluorescent and HMI fixtures. You have to be really careful when choosing a DC-to-AC inverter for film production because there are three basic types of inverters and not all of them are suitable for production applications. Since a blanket assertion like this would not satisfy me, I would like to explain in detail why it matters that you use only "True Sine Wave" Inverters and Power Factor Corrected ballasts.

But first I should mentions that the recommendations I will make are based upon extensive research I have done on the use of portable gas generators in motion picture production. For this research, I ran a series of tests in order to analyze the interaction of the different type of portable generators with the prevalent light sources available today. Since inverter generators use the same three types of inverters, the findings of my research are applicable to stand alone DC-to-AC inverters designed for use with batteries as well. The results of my tests are going to be cited in the upcoming 4th edition of the "Set Lighting Technicianís Handbook." I have also compiled the results in an article for my company newsletter and it is available on our website (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html).

http://www.screenlightandgrip.com/images/generators/Inverter_Con_Gen_SineWave.jpeg
Waveform of power output by conventional generator. Note the frequency error and noticeable distortion (ILLUSTRATION COURTESY OF KIRK KLEINSCHMIDT]

To understand how the application is the same it may help to review why inverters are used in generators in the first place. Even though a conventional generator makes a pretty decent AC power sine wave, it is considered “dirty” power. Measured on an oscilloscope (pictured above), its’ sine wave appears jagged. Those small spikes in the sine wave indicate harmonic distortion that can cause problems for sophisticated electronics, like video cameras, monitors, computers, and hard drives that need a clean sine wave to operate. With the increasing use of personal computers and microprocessor-controlled recording equipment in motion picture production, there is a greater demand for clean, reliable power on sets.

http://www.screenlightandgrip.com/images/generators/MSW_Inverter_Power_Flo.jpg
Step 1: Rectifier Bridge converts multi-phase AC power to rectified sine wave. Step 2: rectified sine wave is flattened to DC. Step 3: micro processor switching alternates wave polarity creating a modified square wave. (ILLUSTRATION COURTESY OF HARRY BOX]

Inverter generators meet this demand for cleaner power by adding an additional step that completely processes the “dirty” AC power from the generator’s alternator. An inverter module takes the raw power produced by the generator's alternator and passes it through a microprocessor controlled multi-step process to condition it. But, rather than using the simple two pole cores of conventional genertors, inverter generators use multi-pole cores and small stators to produce a raw AC power that is multiphase (more than 300 overlapping sine waves), high frequency (up to 20’000 Hz), and upwards of 200 Volts. This high voltage AC power is then converted to DC. Finally the DC power is converted back to low voltage single phase AC power by an inverter. In the process the inverter cleans and stabilizes the power.

There is a popular misconception that you should only use electronic ballasts with portable generators. Where that is true with conventional generators without crystal governors, it is not true of inverter generators. By using a microprocessor to convert AC power to DC, and then an inverter module to convert the DC back to AC, inverter generators generate power that is independent of engine speed and rock solid with a frequency variance of only hundredths of a cycle - which eliminates the need for costly crystal governors. In this limited sense, it can be said that inverters, whether for batteries or built into a generator, are "actually better for use with the HMI electronics." In fact, only one of the three types of inverters are suitable to power HMI lights.

The three types of inverters are, "true sine wave", "modified square wave" (also known as "modified sine wave"), and "square wave." One might wonder why there are so many types of inverters. As John De Armond, explains in his informative article "The “Hows” and “Whys” of Inverters and Inverter Generators" the primary reason is cost. To paraphrase John's article, to make a nice sine wave from DC power (whether generator power or battery power) is expensive. There is a trade-off between cost and waveform purity. An approximation of a sine wave may be created by outputting one or more stepped square waves with the amplitudes chosen to approximate a sine (a "modified square wave" inverter). The more steps, the more like a sine wave the output (a "true sine wave" inverter). However, each of the voltage steps requires its own voltage supply, its own transistor switch, plus the necessary control circuitry. The bottom line is that the more steps, the more expensive the inverter. The two go hand in hand.

http://www.screenlightandgrip.com/images/generators/Inverter_Wave_Comp.jpeg
Ideal Sine Wave (black), Single Step Square Wave (blue), Three Step Square Wave (red)( ILLUSTRATION COURTESY OF JOHN DE ARMOND)

Take a look at the figure above. The black trace is a pure AC sine wave. The blue wave is a single step approximation or square wave. The red wave is a three step wave or simple modified square wave. As is intuitive, the three step wave produces a closer approximation of a sine wave and thus will satisfactorily operate more devices than the single step one. The trade-off is cost and complexity.

http://www.screenlightandgrip.com/images/generators/Inverter_3Step_Module.jpeg
Switch sequence of three step output stage of a modified square wave inverter. ( ILLUSTRATION COURTESY OF JOHN DE ARMOND)

The figure above is a line drawing of a typical three step output stage of a simple modified square wave inverter. The voltages V1 through V3 are increasingly higher DC voltages. A microprocessor generates this pseudo sine wave by sequentially switching S1 through S3 on, S3 through S1 off, S4 through S6 on, S6 through S4 off. It repeats this 60 times a second. Where each of the voltage steps requires its own voltage supply, its own transistor switch, plus the necessary control circuitry, one can intuit that the more steps in the modified square wave, the more complicated and thus more expensive the inverter. Where it is less expensive to make a modified square wave that will satisfactorily operate most construction equipment and RV appliances, than it is to make a true sine wave there is not the cost/benefit return to warrant the incorporation of more switches in inverters manufactured for these markets. This is why there are still three types of inverters available on the market to this day for use with batteries and built into generators.

Square wave (SW) inverters will run simple things like tools with universal motors with no problem, but not much else. For this reason, SW inverters are now found only in the construction trades, where they offer the benefit of being cheaper. For the reasons detailed below, SW inverters have no application in motion picture production.

“Modified Sine Wave”, “Psuedo Sine Wave”, and “Cycloconverter” are all sales terms used for a modified square wave type of AC power generated by inverters with more switching capacity. Modified square wave (MSW) inverters are low in cost and will satisfactorily operate almost all common household appliances and power tools. For this reason, MSW inverters are the most prevalent and the ones typically used in the economy RV/Residential Standby and Industrial lines of inverter generators. Unfortunately, they also are not suitable for use in motion picture production except for the powering of quartz lights. Since I am out of space, I will have to explain in my next post why MSW Battery Inverters and Inverter Generators are not suitable for HD digital cinema productions.


-Guy Holt, Gaffer, ScreenLight & Grip (http://www.screenlightandgrip.com), Boston

[nejuicer]

Cont. from above

MSW Battery Inverters and Inverter Generators are not suitable for HD digital cinema productions because a modified square wave will cause sensitive electronic equipment (computers, hard drives, video cameras) to overheat, and will cause electronic HMI and Fluorescent light ballasts to kick harmonic noise back into the power stream. Furthermore, electrical components that depend on the peak value of the voltage waveform to operate effectively (the diode-capacitor power supplies in computers, hard drives, and electronic HMI ballasts, as well as the bridge rectifiers of battery chargers) will not operate effectively on a modified square wave. In his article "The “Hows” and “Whys” of Inverters and Inverter Generators," John De Armond explians why using the example of a battery charger powered by a rudimentary MSW inverter generator - a Honda EX350.

http://www.screenlightandgrip.com/images/generators/Inverter_ModSineWave_NoLoad.jpeg
Output waveform of a Honda EX350 square wave inverter generator ( ILLUSTRATION COURTESY OF JOHN DE ARMOND)

The illustration above is of an oscilloscope shot of the modified square wave of a Honda EX350 inverter generator. The output of a MSW battery inverter would be almost identical. Notice the Root Mean Square (RMS) voltage indication (on the right side) is 120 volts even though the peak voltage is only 142 volts. A true sine wave with a RMS voltage of 120 would have a peak voltage of 169 volts (120 x 1.414 = 169 volts.) This difference in peak voltages is what makes MSW inverters unsuitable for motion picture production applications. This becomes apparent when we compare the operation of a battery charger on the true sine wave of grid power to its operation on a modified square wave of an MSW inverter.

A battery charger typically consists of a step down transformer, a rectifier and support electronics like charge control circuitry. On each half-cycle of the 60 hz line voltage, the voltage first increases and then decreases in the shape of a sine. The transformer secondary of the battery charger follows this voltage. Connected to the secondary is the rectifier that converts the AC to DC for battery charging. Only when the instantaneous AC voltage exceeds the battery voltage plus the 0.7 voltage drop of the rectifier does current flow to charge the batteries. Photo 5 illustrates this effect. The two lines at “1” and “2” mark on the voltage sine wave where the rectifier starts conducting and causing current to flow.

http://www.screenlightandgrip.com/images/generators/Inverter_ModSineWave_BatCharge.jpeg
(ILLUSTRATION COURTESY OF JOHN DE ARMOND)

Problems arise when a charger of this type is powered by a modified square wave regardless if it is generated by a battery inverter or inverter generator. Recall from the first photo above that the peak voltage of a modified square wave does not rise as high as a sine wave (142 volts verses the 169 volts of a true sine wave.) The horizontal line in the photo above shows about where the modified square wave would reach. In this particular case, the modified square wave would never reach a voltage sufficient to make the rectifier conduct and so the battery would never charge even though power is connected, the LED indicators light up, and a true RMS voltmeter would indicate about 120 volts. Problems also arise when a modified square wave is used to power the electronic ballasts of HMI and fluorescent lights. This becomes apparent when we compare the power waveform induced by the operation of a Quartz Incandescent Light (an Arri 300) to that of a fluorescent fixture that uses Compact Fluorescent Lamps (CFL) operating on MSW inverter (the same Honda EX350.).

http://www.screenlightandgrip.com/images/generators/Inverter_ModSineWave_QuartzLoad.jpeg
Voltage and the current output waveforms of a Honda EX350 square wave inverter generator powering 300W incandescent light ( ILLUSTRATION COURTESY OF JOHN DE ARMOND)

The illustration above is of a scope shot of both the voltage and the current output of the Honda EX350 generator driving a 300 watt Quartz Incandescent light (a resistive load.) As you see, a modified square wave works well for a resistive load like an incandescent light. The current waveform rises and falls with the voltage waveform (they are in phase) and the inherent distortion of the modified square wave does not induce distortion of the current. Things get a whole lot more interesting when we connect a Compact Fluorescent Lamp (CFL) to the modified square wave. As you can see in illustration below the fluorescent lamp creates all kinds of current oscillation that slightly distorts the voltage waveform (creates a spike).

http://www.screenlightandgrip.com/images/generators/Inverter_ModSineWave_FloLoad.jpeg
Voltage and the current output waveforms of a Honda EX350 square wave inverter generator powering fluorescent light (ILLUSTRATION COURTESY OF JOHN DE ARMOND)

Electronic ballasts (both fluorescent & HMI) utilize solid state electronic components (rectifiers, capacitors, and IGBTS) that use only portions of the power waveform - they place all their load on the peak values of the voltage waveform. These devices then return the unused portions to the distribution system as a harmonic current. These harmonic currents stack on top of one another in the distribution system creating harmonic distortion that pulls the voltage and current out of phase. Under certain conditions, these harmonic currents that are kicked back into the power stream by the electronics of the ballast can cause a distortion of the voltage waveform (the spike in the waveform above) that manifests itself as a noticeable audio buzz or equipment to malfunction. For a detailed explanation for why harmonic currents cause voltage waveform distortion see my article on the use of portable generators in motion picture production available on our website (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html).

Fluorescent lights are a good choice for operation on battery inverters in the limited sense that they use a quarter of the power of a comparable tungsten light. However, the ballasts of the many fluorescent fixtures, like the Kino Flo fixtures that use the T-12 tubes (the Single, Double, and 4 Bank Fixtures, the Wall-o-Lite, Flathead 80, and the Image 20, 40, & 80 fixtures) and fluorescent fixtures that use Compact Fluorescent Lamps (CFLs) return harmonic currents into the power stream. For this reason, Kino Flo cautions users, on their website: "Kino Flo ballasts ... will draw double the current on the neutral from what is being drawn on the two hot legs. On large installations it may be necessary to double your neutral run so as not to exceed your cable capacity."( FAQ "Why is the neutral drawing more than the hot leg" at http://www.kinoflo.com/FYI/FAQs.htm#2) For a detailed explanation for why harmonic currents cause unusually high neutral returns see my article on the use of portable generators in motion picture production available on our website (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html).

When you plug a single 4' - 4 Bank Kino into a wall outlet you need not be concerned about harmonic currents causing voltage waveform distortion. The impedance of the electrical path from the power plant is so low, the distortion of the original voltage waveform so small (1-3%), and the plant capacity so large in comparison to the load of the one light, that the inherently noisy load of the 4'- 4 Bank Kino will not affect the voltage at the distribution bus. Since I am out of space, I will have to explain in my next post how it is a different situation when plugging fluorescent fixtures into the inherently distorted voltage waveform of MSW inverters or conventional portable generators.



Guy Holt, Gaffer, ScreenLight & Grip (http://www.screenlightandgrip.com), Boston

[nejuicer]

Cont. from above

When you plug a single 4' - 4 Bank Kino into a wall outlet you need not be concerned about harmonic currents causing voltage waveform distortion. It is, however, an all together different situation when plugging fluorescent fixtures into the inherently distorted voltage waveform of MSW inverters (as seen above) or conventional portable generators (as we will see below.) If we compare the oscilloscope shots below of the voltage waveform induced at the power bus by a Kino Flo Wall-0-Lite (with 10 - 4' T-12 Tubes) operating on grid power (left), power generated by a conventional generator (middle), and power generated by a Pulse Width Modulated (PWM) Inverter generator to the same power sources without a load, we see clearly that the degree of voltage waveform distortion caused by the return of harmonic currents by the Kino Flo T-12 ballasts is directly proportional to the degree of distortion of the inherent power waveform.

http://www.screenlightandgrip.com/images/generators/wwaveform_no-load.jpg
Left: Grid Power w/ no load and a THD of less then 3%. Center: Conventional Generator w/ no load and a THD of 17-19%. Right: Inverter Generator w/ no load and a THD of 2.5%.

The fact that the original supply voltage waveform of conventional generators is appreciably distorted (a THD of 17-19%) to begin with (see middle frame above) causes harmonic currents returned by an electronic Kino ballasts to induce significant waveform distortion of the voltage in the distribution system. The magnitude of current and voltage waveform distortion depends upon the quality of the original applied power waveform and the relative size of the electronic load with respect to the source impedance and capacity of the power system. That is, the amount of voltage distortion increases as distortion of the applied waveform increases and the percentage of electronic ballasts taking up the total capacity of the power system increases.

http://www.screenlightandgrip.com/images/generators/wwaveform_kino.jpg
Left: Grid Power w/ Kino Flo Wall-o-Lite. Center: Conventional AVR Power w/ Kino Flo Wall-o-Lite. Right: Inverter Power w/ Kino Flo Wall-o-Lite.

This is evident in the oscilloscope shots below of an Arri 1200 HMI Par Plus with standard Arri electronic ballasts. The adverse effects of the severe voltage waveform distortion exhibited in the power of the conventional generator below, can take the form of overheating and failing equipment, efficiency losses, and circuit breaker trips. This is because, as we saw above, circuits that depend on the peak value of the voltage waveform to operate effectively (the diode-capacitor power supplies in computers, hard drives, and electronic ballasts), will work sporadically, if at all, on a squared off wave form whether it is created by harmonic currents distorting the voltage waveform (above) or created by the switching of a MSW battery inverter. Common symptoms are computers locking up and other operational malfunctions that are unexplainable.

http://www.screenlightandgrip.com/images/generators/wwaveform_elec_ballast.jpg
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.

On top of that, the excess part of the wave (the shaded area in the diagram below) must be dissipated somehow. This comes in the form of heat. The bigger the current draw from the unit, the more it produces excess heat within the unit that was not factored for in its' original design. Extended exposure to square wave power supplies, and the heat it generates, may eventually cause premature component level failures within the unit. Harmonic distortion of the magnitude above can also create ground loops and radio frequency (RF) interference. For a detailed explanation for why this is, see my article on the use of portable generators in motion picture production available on our website (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html).

http://www.screenlightandgrip.com/images/generators/waveform_harmonics_heat.jpg
Unuseable portion of distorted waveform (shaded) dissipated in heat.


For these reasons, audio/video production equipment, computers, electronic ballasts, and battery chargers require a nearly pure (low distortion) true sine wave input. If these devices are to be run from a battery inverter or an inverter generator, then the inverter must supply a sine wave or something pretty close to it. As discussed at the outset, inverters of this sophistication are appreciatively more expensive - from 2 to 3 times - because of the number of and prohibitive cost of high power electronic switch devices and components required. However, recent rapid developments in the field of IGBT (Insulated Gate Bipolar Transistors) electronics and miniaturization/mass production of microprocessor based digital control systems have reached the stage that Pulse Width Modulation inverter modules are now economically viable and affordable. Since I am out of space, I will have to explain the benefits of Pulse Width Modulation in my next post.

Guy Holt, Gaffer, ScreenLight & Grip (http://www.screenlightandgrip.com), Boston

[nejuicer]

Cont. from above

Pulse Width Modulation (PWM) inverters provide a more sinusoidal current and for that reason are commonly called True Sine Wave inverters. PWM inverters use extremely fast micro-processor control modules to switch Insulated Gate Bipolar Transistors (IGBTs) at extremely high speeds to produce AC power with a "true" sine wave (with full width and amplitude) from DC power (whether from batteries or the rectifier bridge of an inverter generator.)

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Pulse Width Modulated (PWM) Voltage Steps(ILLUSTRATION COURTESY OF SIEMENS CORP)

In the case of "True Sine Wave" inverter generators, the PWM inverter module consists of a converter, DC link, control logic, and an inverter. The converter section consists of a fixed diode bridge rectifier which converts the more than 300 three phase AC sine waves generated by the multi-pole core of the generator's alternator to high voltage DC power. AC Output is then generated from the high voltage DC by the inverter section with voltage and frequency set by a PWM control logic. A highspeed microprocessor switches IGBTs on and off several thousand times a second according to the PWM control logic to create a variable voltage and frequency.

http://www.screenlightandgrip.com/images/generators/Inverter_Gen_SineWave.jpeg
Waveform of power output of PWM inverter generator. Note there no discernable distortion or frequency error. (ILLUSTRATION COURTESY OF KIRK KLEINSCHMIDT]

The "true" sine wave that PWM inverters deliver is more suitable for computers, solid-state equipment with built-in computer functions or microcomputer-controlled functions. Not as cheap as MSW inverters, generator manufacturers only put PWM inverter modules in their deluxe or Super Quiet product lines. For instance, the Honda super quiet EU series of generators employ Pulse Width Modulation (PWM) inverter modules with a waveform distortion factor of less than 2.5% - which is considerably better than conventional generators and quite often better than what you get out of the wall outlet.

Even though "True Sine Wave battery" inverters generate clean stable power, they have limited application in motion picture lighting because they are only capable of limited power output (1800W max.) The amount of power they can generate from a car battery through the lighter socket is further limited by the wiring of the 12V car lighter socket. That is because when voltage goes down, amperage goes up. Wire that carries 12V DC has to be sized considerably larger then wire that carries 120V AC for the same load (wattage.) For instance to supply 12 volts to a 1800W inverter requires 2 ought feeder cable to the car's battery. Also the car's alternator has to be large enough to take the load without burning out (most are not.) The wiring of a car cigarette lighter circuit is typically only sufficient to power a 300W inverter. This is enough power to operate a few fluorescent fixtures, but for the reasons cited above you would want to make sure to use a "True Sine Wave" Inverter.

http://www.screenlightandgrip.com/images/shuttlefilmstrip4lg.jpg
Exo-skeletal pipe rig on shuttle to rig lights and mount 750W batt-verter on front (covered for rain protection)

A better alternative to using a car's lighter socket is a Battery/Inverter set up that is commonly called a "Batt-verter." A "Batt-verter" system consists of one or more deep cycle 12V batteries (usually Marine Cells), a 12V DC-to-120V AC "True Sine Wave" Power Inverter, and a 12V Battery Charger. Batt-verters can work great for traveling car shots but offer limited capacity and run time. Your run time will depend on your load and how many batteries you wire in paralell. Here are some production stills that show you two Batt-verter systems we built to run Kinos to light the inside of an airport shuttle bus for the feature "Shuttle." The first is a 750W "Batt-Verter" rig wired into in a Calzone case and mounted on an Exo-skeletal pipe rig that also held the Kino Flos.

http://www.screenlightandgrip.com/images/shuttlefilmstrip4.2lg.jpg
750W "Batt-Verter" Rig wired into in Calzone case and tied into the Shuttle's alternator

To maximize the running time on however many batteries you use, I suggest you use a "jumper cable" to attach the marine cells to the leads of the car's alternator. That way you can use the car alternator as a generator to run the lights during set up and rehearsals. When it comes time to shoot, shut off the engine and continue to run the lights on the silent Batt-verter alone. Running the vehicle engine between takes charges the batteries so that they will run longer.

http://www.screenlightandgrip.com/images/shuttlefilmstrip3.1lg.jpg
1800W "Batt-Verter" Rig wired into the back of Shuttle

The production stills above and below show you a more elaborate 1800W Batt-verter system that we built to run 16 - 4' Kino T-12 tubes inside the airport shuttle bus. Use this link -  - for details on how we wired it. To supply 12 volts to the 1800W inverter we ran 2 ought feeder to the buses' alternator. And since the shuttle bus was equipped with a wheel chair lift and extensive inside lighting of it's own, it was equipped with an oversized alternator that could bear the 1800W DC load. Even then we were able to run only four 4' - 4 Bank Kinos on our 1800W rig.


http://www.screenlightandgrip.com/images/shuttlefilmstrip3.2lg.jpg
SL&G's custom 1800W Batt-Verter powers 16 - 4' Kino Flo single tubes rigged in the interior and on the exterior of an Airport Shuttle


If you need more than 1800 Watts you have no alternative but to use a generator. I would suggest the Honda EU6500is inverter generator. The Honda is so quiet that all you have to do to record clean sound is move the generator around the corner of a building or operate it out of a van or truck. Since I am out of space, I will have to explain in my next post what makes the Honda EU6500is inverter generator much quieter than any other portable generator available - including the "Crystal Synced" Honda EX5500.



Guy Holt, Gaffer, [url="http://www.screenlightandgrip.com"] ScreenLight & Grip (http://screenlightandgrip.com/html/shuttlemailintro.html[/url), Boston

[nejuicer]

Cont. from above


The Honda EU6500is inverter generator is much quieter than the movie blimped Honda EX5500. Part of what makes the new Honda EU6500is so quiet is it's "Eco-Throttle." "Eco-Throttle" is Honda's trade name for a feature of inverter generators already discussed. It is the name Honda give to the fact that the generator's microprocessor automatically adjusts the generator's engine speed to produce only the power needed for the applied load. It can do this because the PWM inverter of the Honda EU6500is enables it to run at different RPMs and maintain a constant frequency and voltage. Where conventional generators like the Honda EX5500 and ES6500 have to run full speed at a constant 3600 RPM to produce stable 60 hertz (cycle) electricity, a Honda EU6500is only needs to run as fast as required to meet the load demand. Since their engines do not have to run at full speed, and the fact that an inverter generator generates 20% more power per revolution of the engine, makes the Honda EU6500is inverter generator substantially quieter than conventional models. To make them even quieter, Honda has designed a new separate triple chamber construction and a new centralized intake/exhaust system. The net result is that the EU6500is is half as loud (ten decibels) as the comparable EM7000is and ES6500 generators typically found at lighting rental houses. Honda's EU Series generators operate at 34 to 44 dBA at 50 ft. - well below what is required for trouble free location recording and quieter than your typical Crawford 1400 Amp "Movie Blimped" Generator. With sound specs this good all you need to record sound without picking up generator noise is a real distro system that will allow you to move the generator off set but yet keep your plug-in pockets conveniently on set.

My company, ScreenLight & Grip (SL&G), has developed a Gen-set that is designed to take advantage of the benefits of "True Sine Wave" Inverter genertors and recent technological advances in HMI ballast design to create clean stable set power that is capable of operating larger lights (HMIs up to 6kw or Quartz lights up to 6kw), or more smaller lights, off of portable gas generators than has ever been possible before. What we do is tap the Honda EU6500is inverter generator as it is designed for 230/240V markets like the UK, EU, Australia, & India (to name just a few.) By doing so, we gain access to the full 7650 Watt power capacity designed into the generator for these 230/240V markets, but not available in generators manufactured for 120V Markets like North America. We then use a proprietary step-down transformer/distro to convert the full 240V power into a single 60A/120V circuit (7500Watts) capable of power large lights. Finally, where PWM inverter generators, like the Honda EU6500is, generate a nearly pure power waveform, our modified Honda EU6500is is capable of reliably powering more lights than has been possible before.

To maximize the number of HMI & fluorescent lights that can run off our modified Honda EU6500is inveter generator, we offer HMIs and Kino Flo lights with Power Factor Corrected ballasts. For those of you not familiar with Power Factor Correction (PFC), a PFC circuit utilizes a RF Mains Filter to restrict the flow of harmonic currents back onto the supply service. In this fashion, the PFC circuit realigns voltage and current and induces a smoother power waveform at the distribution bus. Formerly only available in large HMI ballasts this advanced electronics reduces voltage waveform distortion and contributes to a more economical use of power than typical HMI and fluorescent electronic ballasts.

The substantial reduction in line noise that results from using PFC ballasts on the nearly pure power waveform of an inverter generator creates a new math when it comes to calculating the load you can put on a portable gas generator. In the past we had to de-rate portable generators because of the inherent short comings of conventional generators when dealing with non-PFC electronic ballasts. The voltage waveform distortion created by non-PFC ballasts reacting poorly with the distorted power waveform of conventional generators limited the number of HMIs you could power on a portable generator to 60% of their rated capacity (4200Watts on a 6500W Generator). The power waveform below left (from my article) is typical of what results from the operation of a 2500W non-Power Factor Corrected load (electronic HMI & Kino ballasts) on a conventional portable generator (a Honda EX5500 with a Barber Coleman Governor.) The adverse effects of the severe harmonic noise exhibited here - overheating and failing equipment, efficiency losses, circuit breaker trips, excessive current on the neutral return, and instability of the generator's voltage and frequency - limits the number of non-PFC HMIs and Fluorescent lights you can reliably operate on the generator.

http://www.screenlightandgrip.com/images/generators/wwaveform_pkg_comp_AVR_In.jpg
Left: Conventional generator power w/ pkg. of non-PFC Elec. HMI Ballasts & Kino Flo Wall-o-Lite. Right: Inverter generator power w/ Pkg. of PFC Elec. Ballasts & Kino Flo Parabeam 400.

For this reason, when your lighting package consists predominantly of HMI and Fluorescent lights, it is important to have power factor correction (PFC) circuitry in the ballasts and operate them on inverter generators. The combination of improved power factor and the nearly pure power waveform of inverter generators makes it possible to power larger lights, or more smaller lights, than has been possible before on a small portable gas generator. For example, the power waveform above on the right, is the same 2500W load but with power factor correction operating on our modified Honda EU6500is Inverter Generator. As you can see, the difference between the resulting waveforms is startling. Even though the load is the same, the fact that it is power factor corrected and the power is being generated by an inverter generator, results in virtually no power waveform distortion. For this reason, sensitive electronic production equipment will operate reliably and without damage on the same power. And, the generator is capable of operating larger, or more smaller, lights than has ever been possible before on a portable gas generator.

http://www.screenlightandgrip.com/images/HD_PP_DemoWS.jpg
Wide Shot of Night exterior scene lit with a pkg. consisting of PFC 2.5 & 1.2 HMI Pars, PFC 800w Joker HMI, Kino Flo Flat Head 80, 2 ParaBeam 400s, and a ParaBeam 200 powered by a modified Honda EU6500is.

The extremely low low line noise exhibited in the inverter generator power waveform above (right) creates a new math when it comes to calculating the lighting load you can put on a portable generator. Where before you could not operate more than a couple 1200W HMIs with non-PFC ballasts on a conventional generator because of the consequent harmonic distortion, now you can load an inverter generator to capacity. And if the generator is one of our modified Honda EU6500is inverter generators, you will be able to run a continuous load of up to 7500W as long as your HMI and Kino ballasts are Power Factor Corrected.

http://www.screenlightandgrip.com/images/HD_PP_Demo_SetUp_Night.jpg
The PFC 2.5 & 1.2 HMI Pars, PFC 800w Joker HMI, Kino Flo Flat Head 80, 2 ParaBeam 400s, and a ParaBeam 200 of our HD P&P Pkg. powered by our modified Honda EU6500is through our 60A Full Power Transformer/Distro

According to this new math, when you add up the incremental savings in power to be gained by using only PFC HMI ballasts, add to it energy efficient sources like the Kino Flo Parabeam fixtures, and combine it with the pure waveform of inverter generators, you can run more HMI lights on a portable gas generator than has been possible before. For example, the 7500W capacity of our modified Honda EU6500is Inverter Generator can power a lighting package that consists of a PFC 2.5kw HMI Par, PFC 1200, & 800 HMI Pars, a couple of Kino Flo ParaBeam 400s, a couple of ParaBeam 200s, and a Flat Head 80. Given the light sensitivity of HD cameras, this is pretty much all the light you will need to light both the foreground and deep background of night exteriors. For more details on how this is accomplished I suggest you read the article I wrote for our company newsletter (mentioned above) on the use of portable generators in motion picture production. Since, the power issues it discusses have been vexing set electricians for years, I highly recommend that anyone responsible for generating power on a set, whether large or small, read this article. The article is available at www.screenlightandgrip.com/html/emailnewsletter_generators.html.)


http://www.screenlightandgrip.com/images/HD_PP_Demo_Transformer-Distro.jpg
A Distro System consisting of a 60A Full Power Transformer/Distro, 2-60A GPC (Bates) Splitters, 2-60A Woodhead Box distributes power from a modified Honda EU6500is. Even though the generator is 100' away to reduce noise, plug-in points remain conveniently close to set.

If tie-ing marine cells into the alternator of a car doesn't give you sufficient power, I would highly recommend our new Gen-set system. The generator is super quiet. The transformer/distro gives you access to more power (7500 Watts continuous)in a larger 60A/120V circuit that is capable of power larger lights or more smaller lights than has ever been possible on a portable gas generator. Use this link (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html) for more information about using inverter generators with transformers for motion picture lighting.

Guy Holt, Gaffer, ScreenLight & Grip (http://www.screenlightandgrip.com), Boston

[Zac C]

nejuicer, I got through about the first sentence, and you got me lost.

But nice to see you on here nonetheless, at least a few people will understand what you are saying.

Also Nice to see another MA guy.

Zac

[Pietro Impagliazzo]

nejuicer, I got through about the first sentence, and you got me lost.

But nice to see you on here nonetheless, at least a few people will understand what you are saying.

Same thoughts. lol

:thumbsup:

[nespark]

nejuicer, I got through about the first sentence, and you got me lost. But nice to see you on here nonetheless, at least a few people will understand what you are saying.

Zac, I highly recommend that you read Guy's article. It will give you more insight into the electrical engineering princples behind what he says and will answer many of your questions. I highly recommend that anyone using HMIs on a set read Guy’s article. While the HMI lighting package he has developed as a result of his tests is new (introduced Jan 09), the set power issues caused by HMI ballasts have been vexing electricians for years. His article explains the electrical engineering principles behind these issues, and how his lighting package resolves them, in a way I have not seen elsewhere.

Whats different about his article is that he undertakes a comprehensive survey of the prevalent lighting and portable power generation equipment and describes how he systematically tested how well they work together. One startling result of his tests, was that if you don’t have access to the newest PFC electronic ballasts, you are better served by using the older magnetic ballasts on an inverter generator like his modified Honda EU 6500is over non-PFC electronic ballasts.The article is available at www.screenlightandgrip.com/html/emailnewsletter_generators.html.

Eileen Ryan, Gaffer, Boston

[Dances With Cameras]

There are portable low-noise generators.

Not cheap though.

[Zac C]

Zac, I highly recommend that you read Guy's article. It will give you more insight into the electrical engineering princples behind what he says and will answer many of your questions. I highly recommend that anyone using HMIs on a set read Guy’s article. While the HMI lighting package he has developed as a result of his tests is new (introduced Jan 09), the set power issues caused by HMI ballasts have been vexing electricians for years. His article explains the electrical engineering principles behind these issues, and how his lighting package resolves them, in a way I have not seen elsewhere.

Whats different about his article is that he undertakes a comprehensive survey of the prevalent lighting and portable power generation equipment and describes how he systematically tested how well they work together. One startling result of his tests, was that if you don’t have access to the newest PFC electronic ballasts, you are better served by using the older magnetic ballasts on an inverter generator like his modified Honda EU 6500is over non-PFC electronic ballasts.The article is available at www.screenlightandgrip.com/html/emailnewsletter_generators.html (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html).

Eileen Ryan, Gaffer, Boston

Oh I'm not in any way saying I'm not reading his article at all,

I was mearly jesting at the amount of "big" words in the article, just joshing the maturity of SU :D

I am in the process of reading it, when I have some time to sit down and understand it all