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Portable Generator for a China Lantern/Kino

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#1 Note Suwanchote

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Posted 10 July 2015 - 01:24 PM

Hi guys,

 

My team and I are shooting the 48HFP tomorrow and we've found out that the location we'll be using will not have any usable outlets. It's a small side house on my friend's property.

I originally was part of a groupbuy for high CRI leds that would be battery powered but those have not arrived. We're bringing only a handful of things, namely 2x 2 bank kinos, and one or two 

LED/CFL bulbs (unknown wattage yet but under 100w) for a china ball setup.

 

I do have an LED wand (icelight) and was thinking of sticking that inside the lantern and then flagging some of the spill but haven't tested that. 

Would it be correct in assuming that (I've never used a power generator), I could rent something like a 2K portable generator (I don't believe the kinos have PFC) and that should be fine?

 

Appreciate the help, thank you.


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#2 JD Hartman

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Posted 11 July 2015 - 08:34 AM

If you're renting a 2k generator (about 1500 running watts), you can afford (the watts) to use a 250 or 500w photoflood bulb in the paper lantern.  .


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#3 Guy Holt

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Posted 15 July 2015 - 05:09 PM

Would it be correct in assuming that (I've never used a power generator), I could rent something like a 2K portable generator (I don't believe the kinos have PFC) and that should be fine?

 

 

Sizing a portable generator for a lighting load can be very complicated. Especially when all of the sources Note plans to use (Kinos, CFLs, & LEDs) are not power factor corrected (pfc.) When you use non-pfc lights sources on generators it matters not only what type of generator you use but also what type of ballasts the lights use. The poor Power Factor and Harmonic Noise that Note’s lights will kick back into the power stream can have a severe adverse effect on the power waveform of some generators, but not others. Since Power Factor is commonly overlooked in choosing generators, I would like to take this opportunity to explain it in detail and show how it affects Note’s choice of generator. 

 

If we look at the technical specifications for the classic Kino Flo 4’–2 bank fixtures, the electronic ballast that it uses has a Power Factor of .54.  What that means is that it draws 2.3 Amps rather than the 1.25 Amps you would think using Ohm’s Law (W=VA.) The difference between the actual current drawn by the two 75 bulbs, 2.3 Amps,  and the 1.25 Amps the two 75 bulbs should draw using Ohm’s Law (W=VxA), is the difference between what is called “Apparent Power” and “True Power.”

 

If, in this case, you were to measure the actual current (using a Amp Meter) and voltage (using a Volt Meter) traveling through the cable supplying the Kino Flo 4’–2 bank ballast and multiply it according to Ohm’s Law (VxA= W) you would get the “apparent power” of the bulb (120V x 2.3A = 276W). But, if you were to instead, use a wattmeter to measure the actual amount of energy being converted into real work (light) by the ballast of the Kino Flo 4’–2 bank ballast you would get the “true power” of the bulb which in this case is specified by the manufacturer as 150W (2x75W/bulb.) The ratio of “true power” to “apparent power” is called the “Power Factor” of the light.

 

A favorite analogy electricians like to use to explain power factor is that if apparent power is a glass of beer, power factor is the foam that prevents you from filling the glass all the way up with beer. When lights with a low power factor are used, a generator must be sized to supply the apparent power (beer plus foam), even though only the true power (beer) counts. With a Power Factor of .54, you must take into account that a Kino Flo 4’–2 bank draws nearly twice the power  (276W) for it’s true power output of 150W.

 

I don’t know about the Ice LED light in particular, but I wouldn’t be surprised if it were not power factor corrected either. I have been testing a lot of LEDs lately and I am discovering that a lot of their AC power supplies are not power factor corrected making them less efficient than what you would think using Ohm’s Law (W=VA.) With power factors as low as .45, LEDs can draw twice the current than a tungsten light of the same wattage. Take for example the Litepanel Sola 4 below. At 40W it should only draw .33 Amps; but with a power factor of .6 it actually draws .58 Amps (To see which LED lights are power factor corrected or not, use this link to see some of the results of my tests.)

 

 

Litepanel_Sola_4_Composite_Sm.jpg

(The 40W Litepanel Sola 4 has a pf of .60 and Total Harmonic Distortion of 77.7%)

 

If you don’t take into account the extra current they will draw and the harmonic currents they will generate, you may find breakers tripping and portable generators running erratically. That is because the greater Apparent Power of Lights with a poor Power Factor is not the only consideration when operating them a generator. When you use lights sources like HMIs, Kinos, CLF lamp banks, and even LEDs,  on generators it matters not only what type of ballasts the light uses, but also what type of generator you use to power it. The harmonic currents that ballasts with poor Power Factor kick back into the power stream can have a severe adverse effect on the power waveform of some generators.

 

Normally, when you plug a HMI, Fluorescent, or LED light into a wall outlet you need not be concerned about the current harmonics generated producing voltage 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, that inherently noisy loads placed upon it will not affect the voltage at the load bus.

 

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. 

 

However, it is an all-together different situation when plugging non-Power Factor Corrected HMI, Fluorescent, or LED ballasts, into conventional portable generators. Given the large sub-transient impedance of conventional 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 fact 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 by an HMI, Fluorescent, or LED ballast will result in significant waveform distortion of the voltage at the power bus (see oscilloscope shots above.)  The waveform distortion caused by these harmonic currents can have a severe adverse effect not only the generator, but also other electronic equipment operating on the same power. There is a video on You-Tube by a Lighting Designer by the name of Kevan Shaw that illustrates just this, but with CFL bulbs which have a similar power factor. 

 

 

In this You-Tube Video, Kevan Shaw compares the effect of equal wattages of CFLs and Incandescent lights on a small portable generator. In his test, he first operates a 575W ETC Source Four Leko with Quartz Halogen bulb on an 850W two stroke conventional gas generator without problem. However, when he tries to operate an equivalent wattage of CFLs (30-18W bulbs) the generator goes berserk. Only after turning off half the CFL Bulbs does the generator operate normally with a remaining load of 15 - 18W CFLs (270 W.) What accounts for the erratic behavior of the generator in this video under a smaller load of CFLs? It is a combination of the poor Power Factor of the CFL bulbs (.5) and the harmonic currents they generate.

 

Even though the 15 CFL bulbs have a True Power of 270W (15 x 18W = 270W ), the Watt indicator on Kevan's generator indicates that they draw twice that in Apparent Power (535W), or have a Power Factor of .5 (270W/535W =.504.) The fact that CFL bulbs consume double the energy (Apparent Power) for the 18 Watts of light (True Power) they generate, is only half the story here. Kevan Shaw’s video also clearly demonstrates the severe effect that loads - like CFLs, HMIs, Kinos, & LEDS -  with leading power factor can have on the governing systems of conventional generators.

 

When Kevan turns off the 18W CFL bulbs one at a time until the generator stabilizes, he is not only demonstrating that 15 – 18W CFL bulbs has roughly the same Apparent Power (535W), according to the generator’s Watt meter, as a 575W incandescent light; but, also that the maximum Leading Power Factor load a 850W conventional generator can operate satisfactorily is 270 Watts (15 – 18W CFL bulbs). Looked at from another angle, 576 Watts of Apparent Power with a Leading Power Factor (16 - 18W CFL bulbs) overloaded the generator, while 575 Watts of Apparent Power with a Unity Power Factor (the 575W Quartz Leko) did not. What accounts for this difference? Since the load is almost the same (576 & 575 Watts of Apparent Power respectively), the only factor that can account for the generator going berserk with the equivalent load of CFL lights is the harmonic currents that they generate, that the Quartz Leko does not. Without a doubt, Kevan Shaw’s video is a clear demonstration of the adverse effect that harmonic currents have on the governing systems of conventional generators.

 

For the same reason that Kevan Shaw was not able to operate more than 270 Watts of CFL bulbs (15–18W bulbs) with a Power Factor of .5 on his 850W generator, Note may not be able to operate his package of Kinos, CFLs, and LED lights on a 2000W conventional generator. The adverse effects of the harmonic currents that non-PFC ballasts generate, so graphically demonstrated in Kevan’s video, limits the total amount of Leading Power Factor loads, as compared to Unity Power Factor loads, that can be reliably operated on conventional generators.

 

These power generation issues have been vexing set electricians for years.  Use this link for an article I wrote for our company newsletter that explains the electrical engineering principles behind these issues and how to resolve them.

 

 

BoxBook.jpg

 

 

This article is cited in the just released 4th Edition of Harry Box's "Set Lighting Technician's Handbook" and featured on the companion website "Box Book Extras." Of the article Harry Box exclaims:

 

"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.screenlig...generators.html.

 

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


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#4 JD Hartman

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Posted 16 July 2015 - 07:17 AM

Hi guys,

 

My team and I are shooting the 48HFP tomorrow and we've found out that the location we'll be using will not have any usable outlets. It's a small side house on my friend's property.

Appreciate the help, thank you.

 

So what did you do?  How did thing turn out?

 

For anyone following this thread, this comes direct from the KinoFlo, "Kino’s latest ballasts models: BAL-457-120U, BAL-427-120U, BAL-227-120U & BAL-127-120U, these are all power factor corrected ballast so they’re almost 1. "


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