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Inverter Generator Necessary?


Daniel Meier

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I want to power a couple of my LED Panels (https://www.bhphotovideo.com/c/product/1316114-REG/yongnuo_yn1200w_yn1200_led_video_light.html) for filming skateboarding outdoors.

Would you recommend using an inverter generator for that purpose or can I use a regular (cheaper) standard generator for that matter?

I am pretty new to the world of gennys. So I have no idea if a simple LED light such as the Yn-1200 falls under the category of voltage-sensitive electronic devices such as laptops or computers, that obviously should only be powered with inverter generators, to avoid damage.

I was also wondering about the difference of using regular tungsten lights with a genny. Do they handle voltage variations better than LED (are they studier in that concern)?

Would be great to get a little insight here.

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Not being familiar with the Yongnuo YN1200W LEDs I can’t speak specifically regarding that light, but I can speak to lights with electronic power supplies in general.  With light sources that use Switch Mode Power Supplies (HMIs, Fluorescents, & LEDs) it matters not only what type of generator you use but also what type of power supplies the lights use. The poor power factor and harmonic noise that non-power factor corrected Switch Mode Power Supplies (SMPS) draw can have a severe adverse effect on the power waveform of conventional generators, but not inverter generators. Under the best of circumstances a 4kw HMI will only draw 38 Amps and you will have no problem operating them on a 6500W portable generator. Under the worst of circumstances a 4kw HMI will draw 52 Amps and you will have nothing but trouble operating them on the generator. Why the difference? Because it depends on whether the HMI ballast is power factor corrected (PFC) and whether the generator is an inverter generator or a conventional AVR generator.

The poor power factor (PF) of lights that use Switch Mode Power Supplies (Electronic HMI, Fluorescent, & LEDs) can cause them to use excessive amounts of power for the wattage of light they generate and draw harmonic currents that can have a severe adverse effect on not only the generator, but also other electronic equipment operating on the same power. Since PFC is not mandatory in this country as it is in Europe, you will encounter many non-PFC HMI, Kino, & LED power supplies.  And, since the adverse effects caused by a poor power factor (PF) go beyond an inefficient use of power, it is well worth understanding power factor.

To understand PF lets first compare the PF of a CFL bulb, and its’ effect on the power supply, to that of an incandescent bulb. While not as sophisticated as an expensive 4kw HMI ballast, the ballasts of CFLs operate on the same basic principle. The AC power supply is first converted to DC by a diode-capacitor circuit and then back to AC by a switch mode converter. The only difference between an HMI ballast and a CFL is the type of AC power waveform the switch mode converter generates. An electronic HMI ballast generates a 60/75Hz square wave, while a CFL generates a high frequency sine wave. In contrast, an incandescent light is a simple resistive load. The high resistance of its tungsten filament creates heat until the filament glows - creating light. As we see in the oscilloscope shot below of a 25W incandescent bulb, the current is always proportional to the voltage (current is represented on the scope as the voltage drop on a 1 Ohm resistor.)

http://www.screenlightandgrip.com/images/generators/Incan_Waveform.jpeg

If the applied voltage is sinusoidal, the current generated is also sinusoidal. That is, the current increases proportionately as the voltage increases and decreases proportionately as the voltage decreases. Since the peak of the voltage corresponds to the peak in current, the voltage and current are also in phase and so have a unity PF (PF of 1.)

The voltage and current waveforms below of a CFL bulb are very different from that of the incandescent light above and also representative of that drawn by non-PFC LED power supplies. The most noticeable difference is that the current, generated by the CFL bulb, no longer proportionately follows the nice smooth sinusoidal voltage waveform supplied to it. Rather, it has been distorted by electrical components in the ballast of the CFL bulb so that it instead consists of high amplitude sharp spikes in current that quickly drop off. Also, the peak of the voltage no longer corresponds to the peak in current. The current now “leads” the voltage by 1.7 micro seconds. The voltage and current are no longer in phase as in the case of an incandescent bulb, but instead exhibits what is called a “Leading Power Factor.” Typical PF of a CFL .55. (the lower the number the worse the PF.)

http://www.screenlightandgrip.com/images/generators/CFL_Waveform.jpg

The distorted current waveform and leading PF exhibited here are also characteristic of LEDs because they operate on similar principles. When it converts the AC supply to DC, LED power supplies likewise use only a portion of the voltage waveform, draws current in high amplitude quick bursts, rich in harmonic currents that stack on top of one another, creating harmonic distortion similar to the CFL. As such, LED power supplies draw more power than it uses to create light. 

One would think that only the less expensive LED lights would not be power factor corrected (PFC), but that is not the case. In a random sampling of lights that I did for one of my articles, the power factor of expensive name brand fixtures ranged from .45 to .63 with total harmonic distortions ranging from 75-85%. Even those that were power factor corrected generated harmonic currents when dimmed. For instance, the PF of the Litepanel Astra 1x1 dropped from .99 to .54 when dimmed 50% (THD increased to 83.2%.) To see the results of my tests use this link.

There is a video on You-Tube by a Lighting Designer by the name of Kevan Shaw that  illustrates the effect that lights with a poor PF can have on conventional generators. In his You-Tube Video, “Compact Fluorescent versus the generator,” (available at http://www.youtube.com/watch?v=LeCqreRMzKM) 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 PF of the CFL bulbs 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 poor power PF loads - like non-PFC CFLs, HMIs, & LEDs - can have on the governing systems of conventional AVR 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 AVR generators.

But that is not all. An even closer analysis of the video also shows that the voltage waveform distortion created by the harmonic currents also affects electronic equipment operating on it. For instance, after turning off 18W CFL bulbs until the generator stabilized, Kevan still does "not get.. all the lamps to illuminate properly." What accounts for the bulbs not illuminating properly even though the generator has stabilized? While the Harmonic Distortion generated by the remaining CFLs is not sufficient to affect the generator governor, it is clearly affecting the CFLs themselves - an indication that, short of affecting the generator's governing system, the voltage waveform distortion generated by harmonic currents will adversely affect electronic equipment operating on the distorted power (use this link for more details.)

The adverse effects of the harmonic currents that non PFC power supplies generate, so graphically demonstrated in Kevan’s video, limits the total amount of Leading Power Factor loads (non-PFC HMIs, Kinos, & LEDs), as compared to Unity Power Factor loads (Tungsten), that can be reliably operated on conventional AVR generators.

For this reason, the conventional wisdom in the past has been to not load the generator beyond 50% when using a lighting package with low PF (non-pfc HMIs, Kinos, & LEDs).  By de-rating the load capacity in this fashion, a Gaffer minimizes the adverse effects of high Harmonic Distortion so that both the generator and the loads placed upon it operate more reliably. However, this conventional wisdom no longer holds true if the ballasts are power factor corrected (PFC) and powered by an inverter generator.

http://www.screenlightandgrip.com/images/generators/wwaveform_pkg_comp_AVR_In.jpg

Left: Conventional generator power w/ pkg. of non-PFC Elec. HMI Ballasts & Kino Flo Wall-o-Lite.  Right: Inverter generator power w/ Pkg. of PFC Elec. Ballasts & Kino Flo Parabeam 400.

For example, the severely distorted power waveform above on the left is caused by a 2500W load (consisting of non-PFC HMI Ballasts & a non-PFC Kino Flo Wall-o-Lite) operating on a conventional Honda EX5500. The nearly perfect waveform on the right is the same 2500W load but with PFC 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 (2500W), the fact that it is Power Factor Corrected, and power is being generated by an inverter generator, results in virtually no voltage waveform distortion.  What this means is that an inverter generator can be loaded to capacity with PFC power supplies. The substantial reduction in line noise that results from using PFC power supplies on the nearly pure power waveform of an inverter generator creates a new math when it comes to calculating the continuous load you can put on a portable gas generator. 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 power supplies are Power Factor Corrected.

For more detailed information on how the power factor and harmonic distortion of LEDs affect generators, I would suggest you read a series of articles I wrote for Protocol (the quarterly journal for ESTA) on the use of portable generators in motion picture production. For more detailed information about the use of HMIs and Kinos on portable generators I suggest you read my article on that subject.   

http://www.screenlightandgrip.com/images/generators/BoxBookForumLinkGenSetMed.jpg

Harry Box, author of “The Set Lighting Technician’s Handbook” has cited this 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.” 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."

 You can find links to all these articles at http://www.screenlightandgrip.com/html/hd_plug-n-play_pkg.html

Guy Holt, Gaffer, SceenLight & Grip, Lighting Rental and Sales in Boston.

 

 

 

Edited by Guy Holt
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47 minutes ago, Guy Holt said:

The poor power factor (PF) of lights that use Switch Mode Power Supplies (Electronic HMI, Fluorescent, & LEDs) can cause them

I think we might have had this conversation before, Guy, but not every switching power supply out there has poor power factor; many of them are corrected. I'm astounded that high-priced products made for the film industry aren't.

Poor power factor also won't, strictly speaking, cause things to use more power, though it might make it look like they do.

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1 hour ago, Guy Holt said:

Not being familiar with the Yongnuo YN1200W LEDs I can’t speak specifically regarding that light, but I can speak to lights with electronic power supplies in general. 

Guy, it may be more helpful to give simple answers to simple questions. I don't doubt the accuracy of your knowledge, but it's not necessary to give us the full-on technical infomercial every time.

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Tungsten will handle anything.  Overvolt, undervolt. It just dims or gets brighter.   There is, of course, a failure point at both ends.

You can dim a tungsten globe till its effectively no longer incandescent.  120v globes can be overvolted too, before they pop.

Don't worry about tungsten and gennys.

For LED's, I've never worried about it either, because the cheap ones are so cheap who cares, just buy another if something happens.

The Expensive versions usually come with really nice power supplies, and at that budget level, inverter generators.

You should be able to rent a nice small Honda 2000i that will do everything you need.  You may be over thinking it.

If you are at the point where you purchased an LED unit and can not afford to replace it should something happen, it might be better to find more money.  Most of the Honda units are inverter setups anyhow.  Depending on what you need to power, you might go with a larger unit.

Harbor Freight makes a 3500w generator which is most excellent, and $700 new.   I used one for a month in the swamp. Never had an issue except low oil when I forgot to check it once.  It powered an M18 without fail.

 

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Looks like is can use NPF batteries?

 

Battery Plate 4 x Sony L-Series (NP-F)

How much run time do you get using 4 of the $ony NPF batteries? Or even an off brand NPF battery.

How much is a little 1000w or 2000w generator cost in Germany?  Cost of petrol?


 

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