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Thread: Electric Generator

  1. #1

    Default Electric Generator

    Can anybody offer any advice/information about electric generators for a small lighting set? Or point me to a thread?

    Thanks,
    Joe

  2. #2
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    Default Re: Electric Generator

    how much power do you need ?
    is it for exterior shoot ?
    or interior ? for many interior if you need 50-100amps - if the locations uses a electric stove or dryer ( 220volts) many electric rental houses have a BOX that will plug into the stove/dryer 220v plug = you then can plug in larger lights into box ( vs. regular house circuits which usually are 20amp ) ...

    in general the under 75amp generators tend to be very noisy.. you usually have to place them down the street ( neighbors) and run long cables IMO they aren't worth the problems.
    step up to a 150amp (and above are very quite) and if you stay under 300amps you should be able to run it without a operator ...

  3. #3

    Default Re: Electric Generator

    I use a Yamaha YG2800I

    http://www.amazon.com/exec/obidos/tg/det...e&s=hi&n=507846

    I use it with mole and kino flourescent fixtures. It puts out a pure sinewave and is very quiet.

  4. #4

    Default

    Quote Originally Posted by ezXit View Post
    …in general the under 75amp generators tend to be very noisy.. you usually have to place them down the street ( neighbors) and run long cables IMO they aren't worth the problems.
    It depends on what generator you use and how you use it. The problem with portable generators even the super quiet Hondas, is that by the time you move them far enough off set that you don’t hear them you have significant voltage drop from the long cable run back to set. To the problem of line loss, you have the added problem that as you add load the voltage drops on portable generators. It is not uncommon for a generator to drop 5-10 volts under full load. The combination of voltage-drop on the generator, and line loss on a long cable run, can cause voltage to drop to the point where HMI and Kino ballasts won’t strike. The effect of line loss on tungsten lights like those x proposes to use can also be dramatic because their output falls off geometrically as the voltage decreases. For example a 1k lamp operating at 90% rated voltage (108V) produces about 68% of its normal light output - your 1kw lamp is now a 650W lamp.

    But, that is not all, as the light intensity decreases, so does the Kelvin color temperature of the emitted light. In the case of fluorescents, HMIs, and LEDs, because their power supplies are typically of a “constant power” type, they will draw more current as the line voltage decreases in order to maintain constant power to the lamp. In the case of generator output, voltage loss translates into an exponential loss in power. That is because, if you double the ampere load on the cable, the voltage drop also doubles, but the power loss increases fourfold. What this means is that when a distribution system has a large voltage drop, the performance of the generator (its maximum effective load) is reduced. For these reasons it is worthwhile understanding the dynamics of line loss and how to mitigate it.


    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.

    The trick to using HMIs & Kinos on portable generators is to use a generator, like the Honda EU6500is, with a 240V-to-120V step down transformer that has a slight voltage boost built into it. The Honda EU6500is inverter generator to begin with is much quieter than the other portable generators and even Honda’s 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 comparable to full size movie blimped generators like the Crawfords. But you can't park a Crawford right on set and record sound without picking up the generator either. With sound specs this good all you need to record sound with a Honda EU6500is without picking up generator noise is a real distro system that will allow you to move the EU6500is off set (like you would a Crawford), minimize line loss over a long cable run, and provide plug-in pockets conveniently close to set. That is where the transformer comes in.

    To record sync sound without picking up any generator noise, all you need to do is add 300' of heavy duty 250V twist-lock extension cable between the generator and a 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 - which is usually all the additional blimping you need with these generators. The heavy-duty 250V twist-lock cable eliminates multiple long cable runs to the generator and minimizes line-loss; as well as, eliminates the sever voltage drop you would have using standard electrical cords (see example below for details.)


    Boost Transformers allow you to adjust for line-loss with a selector switch to maintain 120V on set.

    To assure full line level (120V) on set, use a transformer/distro designed to compensate for the inevitable slight line loss you will have even over an extended run of 250V twist-lock cable. That is, use one designed to slightly boost the voltage on the load side (secondary). With these "boost transformers," 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.


    A good example of how a transformer/distro makes it possible to record clean audio tracks even under the worst of conditions is the indie short "Toothbrush." In this story of mistaken identity produced by Guymanly Productions, a pivotal scene takes place in the middle of a near vacant parking lot of an all night convenience store. With no building or other sound barrier within a reasonable distance to block the sound of the generator, Gaffer Aaron MacLaughlin had no recourse but to put it behind their grip truck as far from set as possible.


    Left: Scene in parking lot. Center: Transformer/Distro hidden behind newspaper box (set 200' in distance.) Right: Generator baffled by truck (Transformer/Distro 300' in distance.)


    As you can see from the photos above, he ran 300' of twist-lock extension cable from the generator to our 60A Full Power Transformer/Distro hidden behind a newspaper box. From the Transformer/Distro he then ran 200' of 6/3 Bates Extension to set where he broke out to 20A Edison receptacles using a 60A snack box. While running the generator near full capacity with a lighting package that consisted of three 1200W HMI Pars and two 1k Baby Quartz Fresnels, he experienced no appreciable voltage drop on set even after a 500' cable run because our Select Transformer/Distro was able to compensate for both the line loss of the cable and voltage drop of the generator under near full load.


    This example shows how the variable boost of a transformer, not only enables you to place the generator further from set where you won't hear it, but also assures that the supply voltage on the secondary side of the transformer does not drop too low. By comparison, had Aaron run 500' of standard 14 Awg electrical cord he would have experienced a line loss alone of 24.5V (according to the line loss table above.) With that severe a voltage drop, his HMI ballasts would probably have cut out from low voltage as he added additional loads on the generator. Without the line-loss compensation of our Transformer/Distros, he would have had to move the generator closer to set where it would be picked up on the audio tracks.

    For more detailed information on using transformers on set, I would suggest you read an article I wrote on the use of portable generators in motion picture production. Harry Box, author of “The Set Lighting Technician’s Handbook” has cited my article in the just released Fourth Edition of the handbook. In addition, he has established a link to it from the companion website for the Fourth Edition of the Handbook, called“Box Book Extras.”


    If you haven't yet read the article, or looked at it in a while, it is worth reading. I have greatly expanded it to be the definitive resource on portable power generation for motion picture production. Of the article Harry Box states:

    "Great work!... this is the kind of thing I think very few technician's ever get to see, and as a result many people have absolutely no idea why things stop working."

    "Following the prescriptions contained in this article enables the operation of bigger lights, or more smaller lights, on portable generators than has ever been possible before."


    The article is available online at http://www.screenlightandgrip.com/ht...enerators.html.

    Guy Holt, Gaffer, ScreenLight & Grip, Lightng & Grip Rental in Boston

  5. #5

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    Quote Originally Posted by ezXit View Post
    if the locations uses a electric stove or dryer ( 220volts) many electric rental houses have a BOX that will plug into the stove/dryer 220v plug = you then can plug in larger lights into box ( vs. regular house circuits which usually are 20amp ) ...

    Those custom distribution panels, called “Splitter Boxes,” that rental houses wired to access more 120V power from 240V circuits and the 240V twist-lock receptacle on generators, worked well enough in the old days when the lighting used in production consisted predominantly of incandescent lights (a linear load.) However, Splitter Boxes are inherently unsuitable to carry the non-linear loads that make up the typical lighting package today - packages consisting predominantly of non-Power Factor Corrected HMI, Fluorescent, & LED Lights. To understand why this is the case, I would suggest you read the article I wrote on the use of Portable Gas Generators in Motion Picture Production that I mention above. The article is posted on our website at: http://www.screenlightandgrip.com/html/emailnewsletter_generators.html.

    To quickly summarize the article: a "Splitter Box" works around the limitations of a 240V wall receptacle or generator power output panel, and provides additional 120V circuits, by splitting out the two 120V circuits that make up the 240V outlet (see generator wiring schematic below.) For the purpose of this discussion, it is important to understand that Splitter Boxes are wired so that their 120V circuits share in the single ground and neutral of the 240V circuit. Splitter boxes worked well enough back when the load on the 240V circuit consisted of only incandescent lights. As long as you roughly balanced your load between the two legs of the generator, phase cancellation between the legs resulted in the neutral return being the difference between the legs. The problem is that things get a bit more complicated with inductive (magnetic HMI ballasts) and capacitive (electronic HMI, Kino, & CFL ballasts) non-linear lighting loads.


    Generator Wiring Schematic

    Since non-linear loads cause current and voltage to be out of sync, the phase currents no longer entirely cancel when they return on the neutral. In addition to pulling the voltage and current out of phase, the Switch Mode Power Supplies (SMPSs) of electronic lighting ballasts create harmonic currents that stack on top of one another, creating very high currents returning to the power source on the neutral wire. If the lighting package consists entirely of non-linear light sources without power factor correction, as much as 80 percent of the current will not cancel out between legs, resulting in very high current on the neutral return even when the legs are evenly loaded. For this reason, on their website Kino Flo cautions users that some of their lights “will draw double the current on the neutral from what is being drawn on the two hot legs... 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”.)

    It is important to appreciate the potential hazard that the harmonic currents generated by SMPS stacking on the neutral can pose. The results of a recent study (illustrated below), showed that the combined effect of the phase shift and harmonics generated by substituting incandescent lamps with an equivalent wattage of CFLs in a house resulted in more than a doubling of the current on the system neutral.


    Substituting a linear load with a equivalent non-linear load in a small single phase distribution system substantially increases the current on the system neutral.

    Since there is no over-current protection on the neutral of a 240V circuit, these currents can lead to overloading of the neutral and potentially a fire like the one that occurred in Vice President Dick Cheney's suite of offices in the historic Eisenhower Executive Office Building next to the White House on December 19, 2007. The cause of the fire that started in an electrical closet on the building's second floor, was found to be caused by an over-loaded neutral wire that resulted from uninformed staff replacing all the incandescent bulbs in the complex with CFLs.

    There is no question that we find ourselves in an analogous situation, since light sources that use Switch Mode Power (HMI, Fluorescent, & LED) have almost entirely replaced incandescent lights as the prevalent lighting source in HD Digital Cinema production packages. To make matters worse, the video cameras, field monitors, hard-drives, lap-tops, and battery chargers that make up the typical location production package also use Switch Mode Power Supplies and hence generator their own harmonics. Where just about every piece of production equipment used on set today generates harmonics, the current returned on the neutral system can be quite high. For example, if say a 6500W generator is loaded to its’ continuous load rating of 5500 Watts with a typical digital cinema production package (consisting predominantly of non-linear loads like video cameras, field monitors, battery chargers, lap tops, hard drives, non-PFC HMI, LED, and Fluorescent lighting fixtures), as much as 37 Amps can be returned on the neutral wire even when the legs are perfectly balanced (Apparent Power Load of 5500W/120V= 46A x.8 = 37A.) Since it is nearly impossible to perfectly balance a load on a splitter box (it requires meticulous attention to loads as you plug in) the return of the neutral is likely to be even higher because of an unbalanced load. Since there is no over-current protection on the neutral of a 240V single phase circuit of a generator (see schematic above) or a house, and the nuetral wire used in a 240V receptacle is only rated for 30A, these currents can likewise lead to overloading of the neutral.

    In this new world of Switch Mode Power, older power generation and distribution systems, like AVR generators and Splitter Boxes, are simply no longer capable of managing the adverse effects of the harmonics that SMPS generate. The 240V circuits they use were designed, not for harmonic generating non-linear loads, but for single phase linear loads like dryers, ranges, heaters, large motors, and compressors, that draw a perfectly balanced load and return no current on the system neutral. For this reason, the neutral wires of 240V circuits on portable gas generators and in houses are simply not sized to handle the higher return current generated by loads that stack on the neutral rather than cancel out. Regardless, if it’s a 240V circuit in a generator or in a house, splitting a 240V circuit designed to power primarily heating elements and compressors, to instead power field production equipment and motion picture lights is an application for which these circuits were simply not designed.

    The only safe way to pull power from 240V wall outlet (whether a three wire or four wire system) is to run your lighting load through a 240v-to-120v step-down transformer with a high K-rating. A transformer converts the 240 volts supplied by these industrial and household 240V receptacles back to 120 volts in a single circuit that is the sum of the two legs of the circuit. For instance, a transformer can make a 60A/120v circuit out of a 30A/240v dryer circuit that is capable of powering bigger lights, like a 5k or 4k HMI. What makes it safe to plug a step town transformer into 240V outlets is that the transformer automatically splits the load of whatever you plug into it evenly over the two legs of the 240V circuit so that you have 100 percent phase cancellation on the generator neutral (primary side); while the neutral wire on the load side of a K-rated transformer (the secondary side) is typically sized to handle higher than normal neutral returns.

    Besides providing effective management of the higher neutral return currents generated by SMPS, a transformer/distro system offers a number of other benefits (covered above) that Splitter Boxes do not. Use this link for more details about using step-down transformers on set: . By giving you access to more house power through common 240V house outlets, a transformer can quite often eliminate the need for tie-ins or generators.


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

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