Generator Adaptation?

fabu00 said:

I am trying to power a 4k HMI with three-prong 50amp paddle from a 5kGenny that only has 240v locking plug. Does anyone know how I can adapt from a 240v socket to female camlock or to 100amp paddle? Or directly to 50amp paddle?

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This is a loaded question because it really depends on the type of 4k ballast and whether the generator is a conventional generator with crystal governor or an inverter generator. Broadly speaking, HMI ballasts now come in two varieties. They are magnetic ballasts and electronic square wave ballasts, also called flicker free ballasts. Electronic square wave ballasts also come in two varieties - those with and those without Power Factor Correction (PFC) (Arri calls it ALF for Active Line Filter.) For the purpose of this discussion, I will not refer to electronic square wave ballasts as flicker free, because that implies that magnetic ballasts generate flicker, which they do not under controlled circumstances.

If possible, instead of a 5000W conventional generator I would recommend you use a 6500W Inverter Generator and a multi-volt electronic ballast with Power Factor Correction (PFC). This combination will be the most reliable and will give you the most options. For those of you not familiar with Power Factor Correction (PFC), a PFC circuit realigns voltage and current and induces a smoother power waveform at the distribution bus. As a result, the ballast uses power more efficiently with minimized return current and line noise. A multi-volt 4kw electronic ballast with PFC (like the Power Gems (PG) 425CDP, the Power-to-Light (P2L) 425LVI, and Arri 2.5/4 EB w/ALF) typically has an operating range of 90-125 & 180-250 Volts. At 120V they will draw approximately 38 Amps, at 240V they will draw 19 Amps on each leg of a 240V single phase power supply, so they are well within the operating capacity of a 6500W generator. Since 4 kw ballasts are typically wired with a 120V 60 or 100 Amp Bates Plug (Stage Pin) you will need a 120V Female Bates to 240V 4pin twist-lock adapter to plug a 4kw ballast directly into the generator.

Depending on the generator you use, you have several options when it comes to operating a 4kw HMI with a non-PFC electronic ballast. Where non-PFC electronic HMI ballasts are also typically auto-sensing multi-volt ballasts (with an operating range of 90-125 & 180-250 Volts), you can also plug them directly into the 30A/240V 4 pin twist-lock receptacle on the generator and they will operate at 240 Volts. However, you will not be able to run a 4k non-PFC electronic ballast reliably on a conventional 6500W generator even though it draws only 26 amps/leg. That is because even though the twist-lock receptacle is rated for 30 Amps, conventional 6500W generators are only capable of sustaining a peak load of 27.5 Amps per leg for a short period of time. Their continuous load capacity (more than 30 minutes) is 23 Amps per leg. And if there is any line loss from a long cable run the draw of a non-PFC 4k electronic ballast will climb even higher. To make matters worse non-PFC electronic ballasts kick a lot of harmonic currents back into the power stream that can cause severe voltage waveform distortion in conventional generators. This harmonic distortion can cause erratic tripping of the breakers on the generator or ballast (for a more detailed explanation of why that is I suggest you read an article I wrote for our company newsletter on the use of portable generators in motion picture production which is going to be cited in the upcoming 4th edition of "The Set Technician's Handbook" - the article is available at www.screenlightandgrip.com/html/emailnewsletter_generators.html. )

In my experience the load of a 4kw non-PFC HMI ballast is too near the operating threshold of 6500W generator for it to operate reliably on conventional (non-inverter) models. That is because the harmonic noise that non-PFC ballasts kick back into the power stream has an adverse effect on the power waveform of conventional generators where it does not on Inverter Generators. Normally, when you plug an HMI light into a wall outlet you need not be concerned about current harmonic distortion producing voltage distortions. 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, that inherently noisy loads placed upon it will not affect the voltage at the load bus.

However, it is an all together different situation when plugging non PFC ballasts ( HMI or Kino) into a conventional portable generator. Given the large sub-transient impedance of conventional portable generators, even a small degree of harmonic noise being fed back into the power stream by a non-PFC electronic ballast will result in a large amount of distortion in its' voltage. Add that the original supply voltage waveform of a conventional generator is appreciably distorted to begin with, and you have a situation where the return of any harmonic currents will result in significant waveform distortion of the voltage at the power bus. For this reason, when your lighting package consists predominantly of non-linear light sources, like 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 reliably power larger lights, like 4ks, on a small portable gas generator.

In the past, the primary factors limiting the use of HMIs on conventional portable generators has been their inefficient use of power and the harmonic noise they throw back into the power stream. The power waveform below left is typical of what results from the operation of a 2.5kw non-PFC HMI load (electronic ballasts) on a conventional portable generator. The adverse effects of the severe harmonic noise exhibited here, can take the form of overheating and failing equipment, efficiency losses, circuit breaker trips, excessive current on the neutral return, and instability of the generator's voltage and frequency. For these reasons it has never been possible to reliably operate more than a couple of 1200W HMIs on a conventional 6500W portable gas generator. Harmonic noise of this magnitude can also damage HD digital cinema production equipment, create ground loops, and possibly create radio frequency (RF) interference. The increasing use of personal computers, hard drives, and microprocessor-controlled recording equipment in production has created an unprecedented demand for clean, reliable power on set.


My company, ScreenLight & Grip (SL&G), has developed a Gen-set that is designed to take advantage of recent technological advances in HMI ballast design and power generation 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 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 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 inverter generators generate a nearly pure power waveform, our modified Honda EU6500is is capable of reliably powering even large HMI lights, like 4ks. For example, the power waveform above on the right, is the same 2500W load but with a power factor corrected ballast 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. And, the generator is capable of operating larger, or more smaller, lights than has ever been possible before on a portable gas generator.

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 harmonic 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). But now, where inverter generators have virtually no inherent harmonic distortion or sub-transient impedance and power factor correction (PFC) is available in small HMI ballasts , this conventional wisdom regarding portable gas generators no longer holds true. 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. According to the new math of low line noise, you can load an inverter generator to 100% capacity.


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. )


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 like our modified Honda EU6500is mentioned above. Honda's sine-wave inverter technology provides much higher quality power than conventional (non-inverter) generators. With a waveform distortion factor of less than 2.5%, the power generated by Honda's EU6500 generator is quite often better than what you get out of the wall outlet. By using an extremely fast microprocessor to switch IGBTs according to a Pulse Width Modulation (PWM) control logic, the power these machines generate is rock solid with a frequency variance of only hundredths of a cycle - which eliminates the need for costly crystal governors. Our modified Honda EU6500is generator provides true sine wave power with low enough distortion, and frequency stability, to power 4k HMIs with magnetic or non-PFC electronic ballasts without problems.


But, since most 4k magnetic ballast operate at 120V and draw 40 Amps, you will not be able to run a 4k magnetic ballast off of the 30A/120V twist-lock receptacle on the generator without tripping it's fuse. The only way to power a 120V 4kw HMI magnetic ballast on a portable gas generator is from its 240V circuit through a 240v-to-120v step down transformer like the one we manufacture to provide access to the enhanced 7500W output of our modified Honda EU6500is. Our 60A Full Power Transformer/Distro will step down the 240V output of the generator to a single 60A 120V circuit that is capable of accommodating the high front end striking load, and even the voltage spikes, of a 4kw magnetic ballast operating at 120V.

There are even benefits to be gained by powering electronic ballasts through our 60A Full Power Transformer/Distro. What's nice about auto-sensing multi-volt electronic ballasts, like the Power-to-Light (P2L) 425LVI ballast, is that if you don't want the one light to monopolize the whole generator, you can plug it in through our 60A Full Power Transformer/Distro. The same ballast will now draw 37 Amps operating the 4kw in 120V mode - leaving room to plug additional lights into our modified Honda EU6500is (through the Transformer/Distro) as well. Given the enhanced 7500W power output of our modified EU6500is, you would still have 23 Amps left over to power additional lights through our 60A Full Power Transformer/Distro. And, as I mentioned previously, if you use only HMI and Kino Flo ballasts with Power Factor Correction you can load our modified Honda EU6500is generator to its' full 7500W capacity. Which means that you can effectively power a 1200W HMI with P2L PFC ballast (11..5A) and a 800W Joker with P2L PFC ballast (8A) in addition to the 4k. And, where these electronic ballasts, "ramp up" gradually during the striking phase, you don't have to leave head room as you would with a magnetic ballast.


If it sounds like Iím hyping the Honda EU6500is generator, it is not because we rent and sell them. As a Gaffer of a lot of tight budgeted historical documentaries for PBS' American Experience and the History Channel, it is my professional opinion that when used with step down transformers these machines are a major advance in portable power. For those who would like to see samples of what can be accomplished with this basic package, I have attached these links to production stills of the PBS and History Channel historical documentaries shot entirely, or in part, with just a couple of transformers and a Honda generator.

The History Channel’s “Unsolved History” episode “Presidential Assassins”

American Experienes Typhoid Mary Biography "The Most Dangerous Women in America"

WGBH’s Ben Franklin Biography “Franklin”

Use this link for more information about powering 4k HMIs on portable gas generators with step-down transformers:  http://www.screenlightandgrip.com/html/hdfilmstrip4lg.html.)

- Guy Holt, Gaffer, Owner/Operator of ScreenLight & Grip - a lighting and grip equipment rental, sales, and production service company in Boston.