Generators

[Sean]

Looking at low-budget, indie shoot that will require a little generator in some locations. I can get a 5000 Watt generator these days for about $1000 Canadian. Most I'd be running at once is a 1K light, 750W, 500W and 250W light. What do you guys think? I've never run lights off a generator before.

[Steven Parker]

Putt-putt gennies like you're talking about are LOUD and usually the outputs aren't really production-friendly. Did I mention how loud those putt-putts are?

Instead of buying something subpar, check around and see if you can rent the putt-putt from a motion picture equipment company. They sound-proof them (as much as possible) and have industry standard distribution outputs. You should be able to get the putt-putt and the cable/distro for a weekly rental at 25-30% of the purchase price you mentioned. And you won't be blowing breakers every 8 minutes!

[Finner]

Not only are the small genny's bad for sound but watch out for the power output from them. many will cause a bad strobe with your lights that will cause big grief.

[vanguy]

We've run with one of those cheap generators where we couldn't run AC, but forget about sound.

As for the image flicker, it would flicker or pulse if you're using HMI or flourescent (Kino-Flo), but incandescent was okay.

[Sean]

Thanks. Good advice all.

[Bruce Allen]

If you're using a small generator, the Honda quiet ones are the best:
http://www.hondapowerequipment.com/ModelDetail.asp?ModelName=eu3000is

They also throttle themselves if you're not drawing full power. Oh, and you can chain them too.

Bruce Allen
www.boacinema.com

[Sean]

And hooking up a converter to a car lighter to give "household current"? Can you even plug a single light into that?

[Ralph Oshiro]

We use putt-putt genies all the time. They're lifesavers! Park them 100' away and throw some sound blankets up. Personally, I've invested in large, portable DC battery systems that have built-in AC inverters. Often sold in marine stores, these run about $200. I can run only small units with it, and no matter how large-a-capacity one I buy, they never seem to be able to strike a KinoFlo ballast (they power regular flourescents just fine). But it'll run a 300W Fresnel for several hours.

[Ralph Oshiro]

And hooking up a converter to a car lighter to give "household current"? Can you even plug a single light into that?
They do work. But you need real heavy-gauge cable running from the inverter to your car battery. Also, you need to keep the car running. Also, way over-spec your Wattage needs--these things burn up pretty quick under load. I mean, they literally "burn up" spewing smoke and everything, even under its so-called "rated capacity" current loads.

[Sean]

Again, awesome info and advice. Thank you guys.

[Eileen Ryan]

Looking at low-budget, indie shoot that will require a little generator in some locations. I can get a 5000 Watt generator these days for about $1000 Canadian. Most I'd be running at once is a 1K light, 750W, 500W and 250W light. What do you guys think? I've never run lights off a generator before.

A $1000.00 generator will run your quartz lighting package without problems because quartz lights are a purely resistive linear load. The problem you will have, besides the audible noise it will create, is the harmonic noise you will generate with non power factor corrected HMI and Kino ballasts.

A gaffer/rental house owner/operator I work with in Boston by the name of Guy Holt has just compiled for his company news letter what is probably the best information regarding the use of portable generators in motion picture production that I have seen anywhere. In his article, he undertakes a comprehensive survey of the prevalent lighting and portable power generation equipment, describes how he systematically tested how well they work together, and has made the results available online at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html. The test consisted of running different loads (quartz, kino, mag HMI, non-PFC HMI, PFC HMI) on each type of generator and grid power as a sort of control.

To paraphrase what he found: harmonic distortion of set power by HMI electronic ballasts is an increasing problem in HD production. It is becoming an issue because portable generators were not designed for the abundance of non-linear loads, like the non power factor corrected electronic HMI and Fluorescent lighting, that make up lighting packages today. The problem is being further compounded by the increasing prevalence on set of sophisticated electronic production equipment like computers, hard drives and HD monitors which require clean power, but are themselves sources of harmonic distortion.

http://www.screenlightandgrip.com/images/generators/waveform_no-load.jpg
Left: Grid Power w/ no load. Center: Conventional Generator w/ no load. Right: Inverter Generator w/ no load.

As the oscilloscope shots above and below (from the article) indicate, when you plug an incandescent movie light into a wall outlet or generator you need not be concerned about current harmonics. As a purely resistive load, quartz lights have very little adverse effect on the waveforms of power generated by a power plant (left shot), a conventional portable gas generator (middle shot), and an inverter generator (right shot.) If anything it has a positive effect on conventional portable generators.

http://www.screenlightandgrip.com/images/generators/waveform_quartz.jpg
Left: Grid Power w/ 2K Open. Center: Conventional AVR Power w/ 2K Open. Right: Inverter Power w/ 2K Open.

However, when you power a HMI movie light with a standard electronic ballast off these same sources it is a different situation. As the oscilloscope shots below indicate, when you plug a standard HMI Electronic ballast into a wall outlet (left shot) you need not be concerned about the current harmonics generated by HMI ballasts 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% THD), and the plant capacity so large, that inherently noisy loads like HMI ballasts placed upon it will not affect the voltage at the load bus.

However, as the middle oscilloscope shot (above) indicates, it is an all together different situation when plugging HMIs into conventional portable generators. Given the large sub-transient impedance of conventional portable generators, even a small degree of harmonic noise being fed back into the power stream will result in a large amount of distortion in its’ voltage. Add to that, the likely hood that the percentage of the generator’s capacity taken up by electronic HMI & Kino ballasts will to be very high given its small size relative to typical lighting packages, and given the increasing prevalence of these types of light sources in production. Finally, add that the original supply voltage waveform of a conventional generator is appreciably distorted to begin with (17-19% THD, see no-load oscilloscope shots above), and you have a situation where the return of any harmonic currents by an HMI ballast will result in significant waveform distortion of the voltage at the power bus as seen in the middle shot above.

http://www.screenlightandgrip.com/images/generators/waveform_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


The adverse effects of the harmonic noise exhibited here, can take the form of overheating and failing equipment, circuit breaker trips, excessive current on the neutral wire, and instability of the generator’s voltage and frequency. It is for these reasons, he argues, that it has never been possible to reliably operate more than a couple of 1200W HMIs with electronic ballasts 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.

In the past, attention was given to generator features such as automatic voltage regulation and crystal speed regulation. But, as the oscilloscope shot above of a standard electronic ballast on an inverter generator indicates, an increasingly more important feature today is the quality of the generated power waveform and how well it interacts with the lighting units predominantly used today. I've run out of space, so I will continue this in my next post

Eileen Ryan, Gaffer, Boston

[Eileen Ryan]

Looking at low-budget, indie shoot that will require a little generator in some locations. I can get a 5000 Watt generator these days for about $1000 Canadian. Most I'd be running at once is a 1K light, 750W, 500W and 250W light. What do you guys think? I've never run lights off a generator before.

Guy Holt’s tests have resulted in some rather startling conclusions. They show that when your lighting package consists predominantly of non-linear light sources, like HMI and Fluorescent lights, it is essential to have Power Factor Correction circuitry (PFC) in the ballasts and to operate them on an inverter generator. The combination of improved power factor and the nearly pure power waveform (1-2 %THD) of the inverter generator creates clean stable set power (like that in the power waveform below right).

http://www.screenlightandgrip.com/images/generators/wwaveform_PFC-ballast.jpg
Left: Grid Power w/ 1.2Kw P-2-L PFC Elec. Ballast. Center: Conventional AVR Power w/ 1.2Kw P-2-L PFC Elec. Ballast. Right: Inverter Power w/ 1.2Kw P-2-L PFC Elec. Ballast.

If you are not familiar with Power Factor Correction (PFC), it is advanced electronics that is typically found in larger HMI ballasts (4kw -18kw) that reduces current spikes and harmonics in the power line and contributes to a more economical use of power than the electronics typically used in smaller HMI ballasts. Until the recent introduction of PFC circuitry in smaller HMI ballasts it was not possible to reliably operate more than a couple 1200W HMIs with non-PFC ballasts on a conventional generator because of the consequent voltage waveform distortion seen above. However, the substantial reduction in line noise (seen in the oscilloscope shot below right) that results from using power factor corrected 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 generator.

http://www.screenlightandgrip.com/images/generators/wwaveform_pkg_comp_AVR_In.jpg
Left: Power waveform distorted by Non-PFC 1200W HMI ballasts on conventional generator.
Right: Near perfect power waveform of the same lights with PFC ballasts on inverter generator.


In the past we had to de-rate portable gas 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, evident in these oscilloscope shots, 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, that inverter generators have virtually no inherent harmonic distortion (1-2% THD) or sub-transient impedance and power factor correction (PFC) is available in small HMI and Kino Flo 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 according to the new math of low line noise, you can load an inverter generator to capacity. And if the generator is one of ScreenLight & Grip’s modified 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 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 lights, and combine it with the pure waveform of inverter generators, you can run more lights on a portable gas generator than has been possible before. For example, the 7500W capacity of ScreenLight & Grip’s modified Honda EU6500is Inverter Generator can power a lighting package that consists of a 2.5kw HMI Par, 1200, & 800 HMI Pars (all with PFC ballasts), 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 all the light needed to light even a night exterior.

http://www.screenlightandgrip.com/images/generators/wwaveform_mag_ballast.jpg
Left: Grid Power w/ 1.2Kw Arri Magnetic Ballast. Center: Conventional AVR Power w/ 1.2Kw Arri Magnetic Ballast. Right: Inverter Power w/ 1.2Kw Arri Magnetic Ballast.

Another startling result of his tests was that If you don’t have access to the newest PFC electronic ballasts, as you can see by the oscilloscope shots above, you are better served by using the older magnetic ballasts on an inverter generator like the Honda EU 6500is over non-PFC electronic ballasts on a conventional portable generator.

I highly recommend that anyone using portable gas generators for set power read his article. While the HMI lighting package he has developed to maximize the production output from their modified Honda EU6500is is new (introduced Jan 09), the set power issues that come with using portable gas generators have been vexing electricians for years. The article explains the electrical engineering principles behind these issues, and how to resolve them, in a way I have not seen elsewhere. In fact his tests will be cited in the upcoming 4th edition of the “Set Lighting Technician’s Handbook.” The article is posted on their website at:
http://www.screenlightandgrip.com/html/emailnewsletter_generators.html (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html)

Eileen Ryan, Gaffer, Boston

[Tim H.]

Sean, the quiet Honda generators are very good. Eileen is right on about Guy Holt, he has done a lot of reasearch in this area.

Have a look at this thread on Cinematography.com where Guy gives more examples and goes into more details http://www.cinematography.com/index.php?showtopic=41743&hl=guy+holt

[Harva Raj]

is the harmonic noise from the generator affects the LED lightings too?