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balancing a generator


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...small portable gas generators (Hondas & such)...
...a Honda EX5500 (a conventional generator)...
...our modified Honda EU6500is Inverter Generator...
...our modified Honda EU6500is...
...our modified Honda EU6500is Inverter Generator...
...modified Honda EU6500is inverter generator...

 

I know you make some reference to 'our website' but it might be appropriate to mention what company you are affiliated with at the top of your post.

 

Just for the sake of clarity. :)

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What Guy says about power factors is right. Here's a shorter and perhaps more accessible look at the basics:

 

http://www.splatco.com/tips/pwrfact/pfarticl.htm

 

It's been a long time since I've had to deal with this directly, so I'm surprised that there's so much undercorrected or uncorrected gear out there. Power factor and how to correct it close to 1 has been well understood for a very long time. Wouldn't the right place to fix this be at the point where rental vendors make their purchasing decisions? If the rental houses would just say "no" to inadequately corrected stuff, we could go back to adding them up and corking them in like we did in the simple old days.

 

 

 

 

-- J.S.

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Bonding between neutral and ground is *requried* at the service entrance, and *forbidden* everywhere else in a simple single family house. There's an exception for an outbuilding such as a garage more than 5 ft. from the main building, where you drive another rod and treat its panel much like a service entrance. BTW, the utility companies typically drive a ground rod at the bottom of the pole where the transformer is, and ground the center tap there.

 

-- J.S.

 

Not universally true. In N.J., U.S.A., the neutral bond in an outbuilding, garage, shed, etc., must be removed in a sub-panel. An additional driven ground rod at the sub-panel is not required or even recommended. Differences in potential between the locations of the two rods will cause more problems than they solve.

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I'm surprised that there's so much undercorrected or uncorrected gear out there. Power factor and how to correct it close to 1 has been well understood for a very long time. Wouldn't the right place to fix this be at the point where rental vendors make their purchasing decisions? If the rental houses would just say "no" to inadequately corrected stuff, we could go back to adding them up and corking them in like we did in the simple old days.

 

So that we could rent a 1200W ballast that our customers could plug equally into a 20A as well as 15A circuit, I asked our Arri rep several years ago why they did not offer power factor correction in their 1200 electronic ballasts. His response was that no body would pay what PFC circuitry would add to the cost of the ballast.

 

While it is true that all major manufacturers include PFC circuitry in HMI ballasts in the 6-18kw range - they do so by necessity. The early line of Lightmaker electronic ballasts (some of which are still kicking around ebay) proved that PFC circuitry was absolutely necessary in large ballasts to reduce heat and returns on the neutral, and to increase ballast reliability. Because of the added cost, weight, and complexity of PFC circuitry, ballast manufacturers in the US have offered PFC circuitry only as an option in medium-sized 2.5-4kw ballasts. And, until very recently manufacturers did not offer PFC circuitry in HMI ballasts smaller than 2.5kw in the US (in the EU PFC circuitry in mandatory in all HMI ballasts sold.)

 

Part of the problem was that PFC circuitry did not offer a huge advantage when plugging into house power. A typical 1200W Power Factor Corrected electronic HMI ballast will draw 11 Amps at 120 Volts verses the 19 Amp draw of a non-PFC electronic ballast. While not a huge advantage when plugging into house power, the added efficiency of a PFC 1200 ballast can make a huge difference when powering a lighting package off of a portable generator. For example, when you consider that a Kino Flo Parabeam 400 draws only 2 amps, the 8 Amp difference between using a PFC 1200W electronic ballast and standard non-PFC 1200W electronic ballast, can mean the difference between running four additional Parabeam 400s on a portable generator or not – I think you would have to agree that is a major boost in production capability and pertinent to any one using a portable generator as their principle source of set power.

 

But that is not the only benefit to using PFC electronic ballasts. The substantial reduction in line noise 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. In the past we had to de-rate portable gas generators because of the inherent short comings of conventional generators with AVR and Frequency governing systems when dealing with non-PFC electronic ballasts. The harmonic distortion created by non-PFC ballasts reacting poorly with the distorted power waveform of conventional AVR generators limited the number of HMIs you could power on a portable generator to 75% 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 according to the new math of low line noise, 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.

 

Except for one notable exception, when manufacturers do offer PFC circuitry in smaller ballasts it is at a premium, adding as much as a $1000 to the cost of a 1200W ballast for instance. The new ballast manufacturer Power-2-Light, on the other hand, is including PFC circuitry in their ballasts at the same price point as other manufacturer’s non-PFC ballasts. But where Power-2- Light is still very new to the market, it is still the case that almost every 575 - 1200 W ballast that you will find in a rental house in North America will be a non-PFC electronic ballast. Don’t blame the rental houses, until recently they never were offered the choice.

 

Guy Holt, Gaffer, ScreenLight & Grip , Boston

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Guy, you seem to have done quite some research into this - this is good! But I think that you've probably lost most of the readers during your text, which is a pity - I think you are going into it a bit too much in depth.

 

I think that is an unfair characterization of our community. While the vast majority will go cross eyed reading Guy's lengthy posts, I think it must be recognized the level of sophistication many of the readers here have. As proved by my project, and about 4 or 5 others I have seen on this site....cinematographers and gaffers are not limited to knowledge about light, lens and film stock.

 

I am sure many here have deep understanding of the physics of electricity and want to read in depth analysis of the issues we face on set every day. I would venture that there are dozens who not only didn't go cross eyed, but was actually able to understand all the issues Guy presents. I know I have a better understanding as a result of reading Guy's work....even if I had to read it 5 or 6 times to fully comprehend.

 

To assume that readers here aren't able or willing to wade through dense electrical theory is doing a disservice to our community. This is one of the best threads in a while, specifically because it has so much information to be gleaned from it...for free no less. (not to mention the people giving the information are obviously well versed in the industry and in the theory...not BSing off something they read on another site.)

 

So keep it up. More information beats less information. I like a dense neg, I like a dense technical read.

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I like a dense neg, I like a dense technical read.

 

Michael, have you checked out that link I gave up in post #27? I think it's a quicker and easier presentation, provided that you at least sort of vaguely remember a little trigonometry.

 

 

 

 

-- J.S.

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Thanks so much to everyone who responded, I really appreciate it.

 

If you fail to balance the generator correctly, what are the negative side effects? Also, when you are striking on or saving the lights, would it be best to do it simultaneously at the source, or turn it off at the generator?

 

Colleen, I wanted to answer you question a little further:

Lets say you have a 3 phase generator{120-208volt} For this example we will use LitePower's configuration with a Basler or Marathon voltage regulator.

As the engine spins the generator around, it passes each "leg" The leg's are spaced equally in a circle, as it passes the leg that is loaded heavy, the engine has to work hard to produce enough power to satisfy the demand{engine slows down a little}, then it passes a leg that is loaded light it doesn't have to work as much so it passes quickly. This will cause engine speed to vary wildly{Hz or Frequency}. Also , most of our 60,120,and 140kw generators use 2 legs to control voltage. The voltage regulators function is to maintain a constant voltage between phase 1 and phase 2 to our pre-set point of 208 volts. As the leg loaded heavy goes by, the regulator looks at it and says"increase" but when it see's the leg loaded light it say's "decrease". Phase 1 could be as much as 20 volts too high, and phase 2 could be 20 volts low, however measured between them you still get 208 volts, measure line to neutral and it wont be 120 volts. This is a bad thing,however some generators use a three phase voltage regulator{this is the case with our 220KW Generators} with a PMG generator{Perm. magnet generator}. This type of generator is much more forgiving in regard to balancing as each leg is adjusted separately.

Also, use the ballast, not the generator's circuit breaker, and ground properly, especially when using dimmer racks.

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So, the moral of the story is start asking for power factor corrected ballasts when you rent stuff. Make it the hot new buzzword, and they'll become available.

 

-- J.S.

 

I think the moral of the story is: understand the principals behind load balancing in single and three phase power systems; how an HMI ballast(s) can an cause un-anticipated increase in current on the neutral; that it's often better to be safe than sorry and double up on your neutral runs. Doubling up on a neutral run isn't the sign of a "hack". A "hack" would be staring at the ground, as he (or she) tries to explain why we just melted the neutral and have to shut down until we can get another stick.

I disagree that asking for PFC ballasts from your rental house will make them appear, they'll appear when it's economically feasible for the rental house to upgrade it's gear. Just as they did when electronic ballasts replaced their more reliable magnetic predecessors.

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John, thanks for that. It was a bit easier to wade through. I only had to read it over 3 times. My question is why do PFC circuits cost so much? How do they work. Obviously they must store inductive kickback and either put it back into the lines in a more orderly fasion, or put it back into the light over time. What components make the cost in 1000s of dollars instead of 100s? Are there large coils or capacitors needed? Even then I can't imagine a coil costing that much.

 

This is my question....just in case I need to start designing cheap PFC ballasts.

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With a purely inductive and resistive load, you can solve the problem with capacitance - and vice versa. My guess is that the problem gets more expensive when the load deviates from a sine wave. It may be more in design than in components. This business is customer driven. The more we ask for it, the harder they'll think about delivering it.

 

 

 

 

 

-- J.S.

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After reading that post, the Colleen Marshalls of the world might think he/she knows enough to accept the next offer to serve as generator operator and end up melting the neutral as happens, or worse creating a hazardous situation where someone takes a lethal shock. It is not always a bad thing to lose readers when discussing the complexity of handling electricity – it creates what I think is a healthy respect for the electrical department. After reading my post and not understanding it 100%, the next time Colleen Marshall is asked by a cost cutting producer to operate a generator so that they can save a few bucks, Colleen Marshall will say no.

 

I already knew that balancing a generator would be a difficult task, and I appreciate the lengthy explanation in the post. I think it is crucial to understand everything Guy Holt included. I will still have to do further research to completely understand everything that was said (hands on and in writing), but I appreciate Guy taking the time to write that out for all of us who still needed the knowledge.

 

Since we ventured further into electricity, does anyone know of any good books about being an electrician on set?

Edited by Colleen Marshall
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Harry Box: Set Technicians handbook is a good read. Taking an adult school/vocational school/technical college, electricians class would be helpful, especially in the area of three phase systems and power distribution.

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My question is why do PFC circuits cost so much? How do they work.

 

Since, this is getting way off the topic of this thread, I have started a new thread ( What is Power Factor Correction in HMIs) to give a detailed answer this question.

 

If you haven't already, I would suggest you read the article I wrote for our company newsletter on the use of portable generators in motion picture lighting. In it I cover some of the basic electrical engineering principles behind harmonic distortion and how it can adversely effect generators. The article is available on our website.

 

Guy Holt, Gaffer, ScreenLight & Grip , Boston

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