Powering HMIs & Kinos with batteries for Night Shoot

[Joe G.]

What's the deal on just adding a couple more 100' extensions and putting it 300' away? Or 500' if necessary? How much voltage do you lose?

 

[Guy Bryan Holt]

Powering HMIs & Kinos with batteries for Night Shoot

With an electronic ballast running kinos and electronic-ballasted hmis you might damage the ballasts simply due to the heat generated by the harmonic resonance they create in the sine wave? Is this correct? ..... realistically, what damage can be done from not using power-corrected ballasts? If the camera is running off batteries and the distortion is minor (a 1200w magnetic hmi and a few kinos on a 6500w honda generator), what are the real-life repercussions of such a set up?

The real-life repercussions of high Total Harmonic Distortion (THD) go beyond equipment getting hot. One adverse effect that I have experienced first hand is that high total harmonic distortion (THD) values, like those in my oscilloscope shots below, cause equipment connected to the circuit to draw more current to maintain the power rating (watts) of the unit. This, in turn, can cause protective fuses on electrical boards of the equipment to blow. I experienced this first hand, when I first tried some year ago to operate a 4k HMI Par on a Honda ES6500 (a conventional AVR generator) with the first generation of electronic square wave ballasts - a Lightmaker. The ballast inexplicably failed when it had never given us problems on mains power. Upon closer inspection back in our shop, we found that a protective fuse on the main board had blown. We replaced the fuse and continued to operate the ballast off of grid power without incident. But as soon as we tried to run it again on the Honda the fuse blew. Since the Lightmaker ballasts are not Power Factor Corrected (PFC), the cause of the ballast's erratic behavior was the amount of harmonic distortion it was feeding back into the power stream generated by the ES6500. The harmonic currents were not a problem on grid power because, given the extremely low impedance of grid distribution, they did not induce voltage distortion. But, fed back into the power stream generated by our Honda ES6500, the same harmonic currents created voltage distortion and sufficient voltage drop from skin effect to blow the protective fuses on the ballast boards.

Left: Conventional generator power w/ THD over 100 percent caused by pkg. of non-PFC Elec. HMI & Kino Ballasts. Right: Same lighting Pkg. but with PFC HMI & Kino Ballasts powered by our modified Honda EU6500is inverter generator. Note the THD is now under 7 percent.​

The upper left oscilloscope shot is of a 2500W non-PFC load on a conventional (non-inverter) generator. Evident here is the voltage distortion at the power bus of our distribution system created by the harmonic currents, or "noise", thrown back into the system by non-PFC ballasts. An artifact of this noise, that is worth noting, is the zigzag saw tooth pattern as voltage ascends from zero potential and descends to zero potential. This zigzag saw tooth pattern is an indication of the existence of high frequency “wavelettes” within the primary sine wave. When interpreting the highly distorted voltage waveform above, it is worth remembering that the square wave depicted on our scope is in fact comprised of many, many voltage spikes, at extremely high frequencies, stacking one on top of the other.

That is, if we were to break out the components making up the square wave we see on our scope it would be comprised of more than just the three orders of harmonics depicted in the example above. It would be made up of many many high frequency waves of a greater amplitude than what we already see in the zigzag portion of the square wave. Each of these voltage spikes is induced by high frequency harmonic currents being thrown back into the power stream by the non-PFC electronic ballasts of our lighting package.

Spectrum analysis of the high frequency Harmonic Currents making up
a Square Wave that can cause Skin Effect and even possibly RF Interference.​

Where THD is as high as what we see in my oscilloscope shots above, the higher frequency harmonics create what is known as "skin effect." Skin effect is a phenomenon where the higher frequencies cause the electrons to flow toward the outer sides of a conductor. Since the flow of the electrons is no longer evenly distributed across the cross sectional diameter of the conductor, more electrons are flowing through less copper and the resistance of the conductor increases. The increase in resistance reduces the ability of the conductor to carry current, resulting in greater voltage drop over shorter distances and overheating of the conductor.

The area of the cross sectional diameter of a conductor used by DC current (left), Low Frequency AC Current (center), High Frequency AC Currents (right).​

I readily concede that ballast performance has improved remarkably since that first generation of electronic Lightmaker ballasts. The latest generation of power factor corrected electronic ballasts have filters built in that reduce the number of harmonic currents the ballast will feed back into the power stream. However, since power factor correction is still not commonly found in HMI ballasts smaller than 2500W, voltage drop from "skin effect" still causes problems when operating HMI lights on conventional portable generators. Especially, since a 1200W non-power factor corrected HMI ballast can draw upwards of 19 Amps on a portable generator, it doesnít take much increase of circuit resistance to push its load over the 20A threshold of distribution circuit breakers. And, given that 1200W ballasts are commonly wired with u-ground Edison plugs rated for 15 Amps, resulting in overheating of the plug end, and an increase of resistance even under normal conditions, voltage drop from "skin effectî" caused by high THD values is what probably accounts for the inexplicable tripping of breakers that anybody who has tried to power HMIs on portable generators is familiar with. Use this
link for more information about the adverse effects of harmonic distortion and how to eliminate it.


Guy Holt, Gaffer, ScreenLight & Grip , Boston

 

[Guy Bryan Holt]

With an electronic ballast running kinos and electronic-ballasted hmis you might damage the ballasts simply due to the heat generated by the harmonic resonance they create in the sine wave? Is this correct? ..... realistically, what damage can be done from not using power-corrected ballasts? If the camera is running off batteries and the distortion is minor (a 1200w magnetic hmi and a few kinos on a 6500w honda generator), what are the real-life repercussions of such a set up?

Total Harmonic Distortion (THD) levels of the magnitude we saw in my oscilloscope shots of my previous post can also create ground loops. That is because return current on neutral conductors with a high Total Harmonic Distortion (THD) value will induce voltage in ground wires greater than the 2 volt maximum stipulated by IEEE Standard 1100-1992 "Recommended Practice for Powering and Grounding Sensitive Electronic Equipment." For example, there was an episode, recently reported on CML, of a pilot shooting in HD that found they had 50 volts between the shield of the SDI line and ground. In that case the problem was fixed by running a "Drain" wire from the SDI Shield back to the Genny via the electrical lunchbox at the DIT station.

When you carry current on the ground wire you create the potential for a ground loop because there will be a slight difference in the voltage between receptacles in the power distribution system when a current is induced on the ground. Under these conditions, a ground loop will occur if there is also more than one ground connection path between two pieces of equipment. Under these circumstances, the duplicate ground paths form the equivalent of a loop antenna that very efficiently picks up interference currents. Lead resistance transforms these currents into voltage fluctuations. As a consequence of ground loop induced voltages, the ground reference in the system is no longer a stable potential (a floating ground), so signals ride on the noise. The noise becomes part of the program signal. The result is that the unwanted signal will be amplified until it is audible and clearly undesirable. Whenever you have current on the grounding system (induced by high THD on the neutral), as well as the multiple connections between electronic components that is typical of HD production packages, there is the potential for a "ground loop."

Interference bars caused by current induced on a ground loop by high THD. ​

Small voltage differences just cause noise to be added to the signals. This can cause an audio hum, interference bars to video signals (above), and transmission errors in computer networks. Higher currents can cause more serious problems that can damage equipment like sparking in connections and burned wiring. As more and more electronic components, like lap top computers, hard drives, and HD monitors, are integrated into the typical location HD production package, ground loops become more of a hazard.

The first step in mitigating the problems caused by harmonic currents is to eliminate the currents. Where customarily the largest source of harmonic currents in a typical lighting package are HMI and Fluorescent lights, using only ballasts with power factor correction (PFC) circuitry will go a long way in reducing the number of harmonic currents in the power stream. 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. PFC circuits successfully increase the power factor to as much as .9, 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.

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 second step in mitigating the problems caused by harmonic currents is to use inverter generators. The combination of improved power factor and the nearly pure power waveform of inverter generators makes it possible to reliably 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.

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​

The extremely 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.

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.​

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 (which are also PFC), 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. Use this link -www.screenlightandgrip.com/html/emailnewsletter_generators.html - for more information about the benefits of low line noise.

Guy Holt, Gaffer, ScreenLight & Grip , Boston

 

[Guy Bryan Holt]

What's the deal on just adding a couple more 100' extensions and putting it 300' away? Or 500' if necessary? How much voltage do you lose?

Unfortunately, there is no easy way to calculate line loss because it is a function of the load relative to the wire gauge and ambient temperature. I once had a situation where nothing more than an Arri 300 caused a brown out. The general rule of thumb is that you start off with wire that is rated for your load. If you need to run more than 200 ft you should bump up to the next larger wire size. You will have sufficient line loss running 300-400 ft to cause your HMI ballasts not to strike. It is impractical and not necessary to place your generator so far away. Matt had a good suggestion in his post:

The honda inverter generators are cheap and surprisingly quiet. .... You can rent a U-Haul filled with blankets or something and run the generator inside the van with one door open facing away from camera as a sort of "blimp" and as a way to move the generator. You can run a 2.5k and a 1.2k plus more, or a 4k and a little more off a single 6500..

I agree with Matt completely. Since Honda introduced their EU series of inverter generators it is possible to record location audio without picking up generator noise - especially if you use them with a transformer. The Honda EU6500is inverter generator to begin with is much quieter than the older movie blimped Honda EX5500. Part of what makes the new Honda EU6500is so quiet is it's "Eco-Throttle." The Eco-Throttle'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 inverter technology 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 given the fact that an inverter generator generates 20% more power per revolution of the engine, makes the Honda EU series of inverter generators substantially quieter than conventional models.

The net result is that the EU6500is operates between 34 to 44 dBA at 50 ft. - half as loud (ten decibels) as the comparable EM7000is and ES6500 generators and well below what is required for trouble free location recording. 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 while minimizing line loss over a long cable run and provide plug-in pockets conveniently close to set. That is where the transformer comes in.

To maximize the number of lights that you can run off the generator, I would suggest you run all your HMIs on Power Factor Corrected ballasts. This will not be easy because until recently Power Factor Correction (PFC) has not been readily available in smaller HMI ballasts in this country, and not always available in 2500 and 4000 Watt ballasts. The reason to use only PFC ballasts is because they contain circuits designed to reduce current spikes and harmonics in the power line. A PFC circuit also causes the ballast to use power more economically than typical electronic ballasts. For example a PFC 1200W ballast will draw 11.5 Amps at 120V where a non-PFC 1200W ballast will draw 19A. Since they draw less power, PFC electronic ballasts enable the operation of both larger HMIs, or more smaller HMIs, off of portable generators. PFC ballasts, used in conjunction with a modified Honda EU6500is and a step-down transformer/distro, can go a long ways towards eliminating the need for large diesel generators in situations like this.

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 generators and PFC 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 the US. We then use a proprietary step-down transformer/distro we have developed to convert the full 240V power into a single 60A/120V circuit (7500Watts) capable of powering large lights. And, 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 inverter generator, we offer small HMIs (200-1200 Watts) and Kino Flo lights with Power Factor Corrected ballasts. The substantial reduction in line noise that results from using PFC ballasts on the nearly pure power waveform of an inverter generator enables the use of larger lights, or more smaller lights, than has been possible before on a small portable gas generator.

Finally, to record sync sound without picking up any generator noise, all you need to do is add 100' - 150' of heavy duty 250V twist-lock extension cable between the generator and our Full Power Transformer/Distro. This is usually enough cable to place the generator around the corner of a building, or to run it out of a van or truck as Matt suggests - which is usually all the additional blimping you need with these generators. The heavy-duty 250V twist-lock cable eliminates multiple cable runs to the generator and minimizes line-loss; as well as, eliminates the voltage drop you would have using standard electrical cords.

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.​

To assure full line level (120V) on set, our 60A Full Power Transformer/Distro is designed to compensate for the slight line loss you will have over an extended cable run. That is, it is designed to slightly boost the voltage on the load side (secondary) so that if you were to feed the supply side (primary) of the transformer 240 volts from the generator, 127 volts would come out on the secondary side where you plug in the lights. This slight boost enables you to place the generator further from set where you won't hear it, yet assure that the supply voltage on set does not drop too low. Our 60A Full Power Transformer/Distro is equipped with a 60A Bates and three 20 A Edison circuits so that you have plug-in pockets conveniently on set.

60A GPC (Bates) Splitters and Woodhead Box.​

Our new 60A Full Power Transformer/Distro offers a number of other benefits as well. Without our Transformer/Distro you can never fully utilize the full power of the generator because the load of a light has to go on one circuit/leg of the generator or the other. For example, when plugging lights into the factory installed power outlet panel of a Honda EU6500is, you quickly reach a point where you can't power an additional 1200W HMI because there is not 11.5 amps (w/ a PFC ballast) available on either one of the factory installed 20A outlets/leg of the generator. With our Full Power Transformer/Distro you can still add that 1200W HMI because the Transformer/Distro not only accesses more power (7500 Watts) through a higher rated circuit (60 Amps), but it also splits the load evenly over the two legs (5.75A/leg) of the generator. The end result is that the generator is capable of handling a larger load more easily because it is a perfectly balanced load.

60A Woodhead Box running Power-to-Light PFC 800W ballast (left) and PFC 1200W ballast (right.)​

Another benefit to using ourTransformer/Distro is that it greatly simplifies set electrics by splitting the load of what ever you plug into it automatically. This means you no longer have to carefully balance the load over the generator's two 20A/120 circuits/legs as you plug in lights because the Transfomer/Distro does it for you. With our modified Honda EU6500is you simply plug in lights until the load wattage displayed on the generator's iMonitor reaches 7500 Watts. Now that you are able to fully utilize the generator's available power, you are able to power larger lights, or more smaller lights, than you could without a transformer/distro. For more details on the use of transformers for set power, I suggest you read the article I wrote for our company newsletter (mentioned above) on the use of portable generators in motion picture production. Use this link -
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 , Boston

 

[Charles Angus]

Guy,
While I'm sure we all appreciate your in-depth explanations and analysis, I think a link to your article would suffice... It breaks the continuity of the thread to have long discussions about total harmonic distortion and power factor correction.

Isabelle,
I am certain that you will find batteries to be significantly less economical than renting put-puts, and probably less economical than a grip truck.

By my math, to run a 3000 watt package (an extremely conservative estimate for a night shoot) you would need 900 kg of lead-acid batteries to run your shoot for 12 hours - that's a lot of batteries!

If you haven't tried the Honda inverter generator, do so. They are incredibly quiet when compared with the older generation (not to mention smaller and lighter). They are now a credible alternative to blimped gennies for many purposes. They can also save your electric crew time and trouble if you get a few of them and place them strategically to eliminate long cable runs.

Cheers,
Charles Angus Taylor

 

[Guy Bryan Holt]

Guy,
While I'm sure we all appreciate your in-depth explanations and analysis, I think a link to your article would suffice... It breaks the continuity of the thread to have long discussions about total harmonic distortion and power factor correction.

The Xantrex Prosine 1800W "True Sine Wave" Inverter costs roughly $1000.00 more than Xantrex's 1750W MSW Inverter. A Honda EU6500is inverter generator can cost anywhere from $1500 - $3000 more than an conventional AVR generator of the same wattage. A difference in cost of that magnitude requires justification. If my posts are excessively long and detailed, it is to arm you with the ammo you will need to justify to a Producer why they should spend a $150/day to rent a Honda EU6500is when the producer wants to rent a generator for $35/day from a tool rental company. In this economy Producers no longer accept platitudes like "because it is better."

Isabelle,
I am certain that you will find batteries to be significantly less economical than renting put-puts, and probably less economical than a grip truck. By my math, to run a 3000 watt package (an extremely conservative estimate for a night shoot) you would need 900 kg of lead-acid batteries to run your shoot for 12 hours - that's a lot of batteries!

Apparently my posts haven't been detailed enough. I was not suggesting that Isabelle buy/rent 900Kg of lead-acid batteries to run her shoot overnight. I was suggesting that she could maximize the running time on however many batteries she does have by tying them into the alternator of a car or truck with a "jumper cable." That way she can use the car/truck alternator as a "generator" to run the lights during set up and rehearsals. When it comes time to shoot, she would shut off the engine and continue to run the lights on the silent Batt-verter alone. Since we spend most of our production day setting up and rehearsing shots, running the vehicle engine between actual takes, to charge the batteries as they are being depleted by the lights, will greatly extend the life of the batteries.

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​

In the example I gave (pictured above) of a custom Batt-verter system that we built to run 4 - 4' 4 Bank Kinos to light the inside of an airport shuttle bus for the feature "Shuttle" that was shot here in Boston on the Viper, we were able to run the lights all night, and night after night, on two 70A hour deep cycle marine cells. You can use this link - www.screenlightandgrip.com/html/shuttlemailintro.html - for more information on how we wired it into the shuttle bus.

Guy Holt, Gaffer, ScreenLight & Grip , Boston

 

[Charles Angus]

Apparently my posts haven't been detailed enough.

I think that was kind of my point, that people check out when presented with that much information in a forum. I've followed your posts on CML, as well, and am familiar with your research into THD and PFC ballasts. You're right, though, I missed your post about using alternators.

I guess my point was just that you could have all of your info on a website (which you do, I think) and link to it from a post saying, "Look into PFC-corrected ballasts, as I have found them to be significantly more efficient. Look here for more info". I think you would find people more inclined to hear you out.

But that's just me.

I was not suggesting that Isabelle buy/rent 900Kg of lead-acid batteries to run her shoot overnight. I was suggesting that she could maximize the running time on however many batteries she does have by tying them into the alternator of a car or truck with a "jumper cable." That way she can use the car/truck alternator as a "generator" to run the lights during set up and rehearsals. When it comes time to shoot, she would shut off the engine and continue to run the lights on the silent Batt-verter alone. Since we spend most of our production day setting up and rehearsing shots, running the vehicle engine between actual takes, to charge the batteries as they are being depleted by the lights, will greatly extend the life of the batteries.

But how much more would a solution like that cost than just using inverter gennies with sufficient cable runs to eliminate noise?

On your site, you list a 750w Batt-verter for $60 a day, and a 7500w genny for $180 day - to get the same output from batteries as from the genny, you would need to spend $600/day on inverters alone (not to mention batteries).

Just saying...

 

[Kim Frank]

Guy thank you for you're detailed information. I will study it cause you're right today one has to really know.

Isabella if all the options don't work for you I would really consider in making it a day for night/ visual effects shot and just faking you're car headlights in post. It's relativly easy to do so and mabe some effects are already budgeted. If so it should be no problem for the compositor to add the lights realisticly.
For a breaf example you could check out the day for night toutorial on videocopilot.net.
That's what I would do, because some hours compsiting are often cheaper than doing and eventually screwing it on set.

 

[David W. Jones]

Bottom Line.... Either you have the budget to shoot the scene or you don't.
If you don't, find an alternative that will fit your budget.

 

[Guy Bryan Holt]

But how much more would a solution like that cost than just using inverter gennies with sufficient cable runs to eliminate noise? On your site, you list a 750w Batt-verter for $60 a day, and a 7500w genny for $180 day - to get the same output from batteries as from the genny, you would need to spend $600/day on inverters alone (not to mention batteries).

I completely agree that a Honda EU6500is properly outfitted is the more cost effecitve solution. But for those situations when a generator simply can't work (traveling car shots for instance) an inverter tied into the car alternator is a viable solution.

Point of clarification, at $60/day our 750w Batt-verter includes batteries wired into the Calzone case.

- Guy Holt, Gaffer, ScreenLight & Grip, Boston, MA

 

[Chris Kennedy]

I once powered a 400 hmi with the Anton Bauer QBH-HD Quad battery holder. It's powered by AB batteries. I don't know the most power you can output through it, I'm no gaffer. This definitely won't be powerful enough to backlight a forest. But it's better than nothing & quiet.