HMI Questions

[Evan Andrew John Prosofsky]

Hello,

I have a few questions about HMI's that have always made me curious.

 

1. What are the differences, pros/cons of magnetic vs. electric ballasts?

2. Being that brand new HMI's are so expensive, is there anywhere other than ebay that specializes in selling used HMI equipment?

3. Excuse my ignorance, does PAR mean you can plug the light in to an ordinary household circuit?

 

Thankyou!

[Chris Keth]

Hello,

I have a few questions about HMI's that have always made me curious.

 

1. What are the differences, pros/cons of magnetic vs. electric ballasts?

2. Being that brand new HMI's are so expensive, is there anywhere other than ebay that specializes in selling used HMI equipment?

3. Excuse my ignorance, does PAR mean you can plug the light in to an ordinary household circuit?

 

Thankyou!

 

1. Magnetic ballasts are very heavy and don't have the "flicker free" option that electronic ballasts so. Electric ballasts are somewhat more fragile and have higher repair costs and are more expensive in the first place.

 

2. Not sure about that one.

 

3. PAR stands for Parabolic Aluminized Reflector. It's a fixture with a very efficient reflector and interchangeable lenses. They are the most common type of HMI fixture, at least in the smaller sizes. The other option is a fresnel. You can plug the smaller ones, like 1200s, into a household circuit.

[Evan Andrew John Prosofsky]

Thanks! So anything under 1200W can be plugged in to a household circuit? What was it that determines that, the amperage? 12 or 13 is maxing out your circuits right? How come 4k, 12k, 18k aren't available as PARS?

 

Anybody know where I can buy some used HMI's, or just cheap HMI's in general, he he

[Michael Collier]

1. Magnetic ballasts set their running frequency against the cycles on the AC power coming in. If your power isn't exactly 50 or 60 hrz, you can have flickering on camera. Not a big problem on xstal sync gennys, but if you can only get a put put you need an electronic ballast. Electronic set their frequency internaly with their own xstal, so they can accept a widder spectrum of power conditions. Also with flicker free you have a little more freedom in frame rate/shutter speed without visible flickering presenting.

 

2. Power brokers, but I beleive they won't just sell one. Great if you need to drop 25k into lights, but not so great if you just want one 1200. There must be other places, I sure others can chime in if they know.

 

3. Par means Parabolic Reflector. The light is positioned inside a parabolic mirror, so light output is controlled very acurately. Instead of having a flood/spot control like a fresnel, you have a kit of lenses you drop in front of the PAR to control its beams spread. You can plug any HMI light into house power up to 1200w. After that the striking draw might pop your breaker, and even if not a 1200w head uses close to 2000w due to inefficiency in the ballast.

[Chris Keth]

Thanks! So anything under 1200W can be plugged in to a household circuit? What was it that determines that, the amperage? 12 or 13 is maxing out your circuits right? How come 4k, 12k, 18k aren't available as PARS?

 

Anybody know where I can buy some used HMI's, or just cheap HMI's in general, he he

 

I know 4 and 6ks are available as pars. I don't know about the larger fixtures.

[David Mullen ASC]

There are 12K HMI PAR's...

 

Typical household circuit (not outlet, since multiple outlets can be on one circuit) is rated for 20 amps in the USA, though some houses, especially older ones, have smaller circuits, 15 amps, maybe even 10 amps.

 

General rule is that you can plug up to 2K total for 20 amps (thus 1K total for 10 amps, etc.) 2K actually draws a little less than 20 amps, but it gives you some wiggle room.

 

Remember that's total, so be aware of whatever else is also drawing power on the same circuit (like a refrigerator, or other lights.)

 

Go to the fuse box and figure out which outlets go with which circuits and then label the breaker box switches and the outlets of the house. If you can't do that, generally (not always) outlets that share the same circuit run along the same wall or near each other.

 

A 1200w HMI unit is generally the most powerful HMI you can plug into a normal 20 amp household circuit.

 

Some old houses still use screw-in circuit breaker bulbs, not switches, so you may need to carry some spares if you blow the circuit.

[Guest Evan Pierre]

To add to what David said some newer houses have larger circuits designated for special power needs. For example I had to map the circuits of a residential home for a shoot last saturday and found that the garage had a single 60 amp circuit. It had been specially installed there because of the washer and dryer. With those unplugged I was able to run two 2K's and one 1K on a single circuit without tripping the breaker (I didn't try three 2ks). Things such as hot tubs, washer and dryers, maybe refrigerators (less likely), etc. can have special larger circuits installed for them. Always be sure to check the breaker for these special circuits, never assume that because there is a washer and dryer that there is a larger circuit to go with it.

 

**Note: When I say I plugged multiple lights in to one circuit, I was plugging them in to two separate outlets that were on that same circuit.

 

Also it is pretty important to map circuits in residential homes before your shoot. The house that I mapped had been recently remodeled and had a new circuit breaker installed. The owners told me that the circuits were already labeled so I thought it would be a pretty simple matter of double checking. My favorite part of the entire day was flipping open the box and being greeted by four circuits all labeled with the same name: plugs. :lol:

 

I use a combination of a GB Instruments Audible and Visual Circuit Tracker ($40 on Amazon) and a Sperry Instruments Outlet Tester ($15 on Amazon) to map basic household circuits. The GB Tracker works best when there is no power being pulled on the circuit while testing, if there is you get some pretty massive interference.

 

I hope this info helps, best of luck!

Edited November 29, 2008 by Evan Pierre

[Rob Vogt]

Also this is assuming you are in America or Japan where the voltages are relatively similar (120 and 110 respectively). I don't know what houses are most commonly rated for in Europe but since they use a 220v system you'll need half as many amps for the same wattage. So Assuming they run on a 20 amp system as well you can plug in a 4k.

Just remember this VoltsxAmps=Wattage. (W/V=A is probably a more useful form of this equation)

 

Be extra careful with the higher voltages too.

Edited November 29, 2008 by Rob Vogt

[Simon Wyss]

As of today we have 235 Volt nominal in the mains, through the day around 233 V.

[Evan Andrew John Prosofsky]

Thankyou very much for the helpful information, everybody. It's superb that an amateur like myself can talk to a site filled with professionals willing to help.

[timHealy]

I know 4 and 6ks are available as pars. I don't know about the larger fixtures.

 

The Arri Max is an 18k par.

 

best

 

Tim

[Robin R Probyn]

Also this is assuming you are in America or Japan where the voltages are relatively similar (120 and 110 respectively). I don't know what houses are most commonly rated for in Europe but since they use a 220v system you'll need half as many amps for the same wattage. So Assuming they run on a 20 amp system as well you can plug in a 4k.

Just remember this VoltsxAmps=Wattage. (W/V=A is probably a more useful form of this equation)

 

Be extra careful with the higher voltages too.

 

 

Dont want to be picky ,but just incase some one is going there.... Japan is 100V... and sometimes less !!! bring your Kino,s !

[Rob Vogt]

Dont want to be picky ,but just incase some one is going there.... Japan is 100V... and sometimes less !!! bring your Kino,s !

Whoops my bad 110 US 100 Japan. And I'm living in Kyoto now I should know this. BTW If you do come here to film bring 3 to 2 prong converters, grounded outlets are rare here.

Matane

[Damien Bhatti]

Is there any alternative for flicker free lighting, than the expensive HMI route?

[Ralph Keyser]

Is there any alternative for flicker free lighting, than the expensive HMI route?

 

Was that question really meant to be "Are there cheap flicker-free HMI lights?" Tungsten lights are flicker free, for example, and very inexpensive. Other lighting sources (including magnetic ballast HMI's) are flicker free under the right conditions. HMIs, however, are fairly unique lights. They are basically an electric arc in an exotic gas environment, and they give you a tremendous amount of light out per watt in, so they are very efficient sources. Unfortunately, that arc is complex to maintain (thus the need for a ballast), and the lamps themselves are expensive to produce.

 

If what you're really looking for is cheap HMI's, then life gets a bit more complicated. Sometimes a production company will fold and sell their equipment. Occasionally rental houses will sell off older units. And sometimes you might find a deal on-line. Just be aware that HMI's are expensive to maintain, so if you get a really screaming deal on one, it might be because it has issues.

[JD Hartman]

Can you shoot video or film successfully using HMI(s) with magnetic ballasts? Of course you can. For one thing, electronic ballasts with the "flicker free option" didn't always exist. If you are running your lights off utility power (the "grid", mains, etc.), the frequency is tightly regulated by the power generation company. There should be no problems unles you are shooting at a shutter speed that isn't "safe" at 60Hz (50Hz in Europe and elsewhere).

[Damien Bhatti]

Was that question really meant to be "Are there cheap flicker-free HMI lights?" Tungsten lights are flicker free, for example, and very inexpensive. Other lighting sources (including magnetic ballast HMI's) are flicker free under the right conditions.

 

Do they remain constant hooked up in a domestic setting as well?

[Rob van Gelder]

as long as the "domestic" is powered from the grid. When used with separate generators....... no guarantee.

[Guy Holt]

some newer houses have larger circuits designated for special power needs. For example I had to map the circuits of a residential home for a shoot last saturday and found that the garage had a single 60 amp circuit. It had been specially installed there because of the washer and dryer. With those unplugged I was able to run two 2K's and one 1K on a single circuit without tripping the breaker (I didn't try three 2ks). Things such as hot tubs, washer and dryers, maybe refrigerators (less likely), etc. can have special larger circuits installed for them.

 

You have to be really careful when using dryer plugs as you have described. Yes, under certain conditions you can use them to power lights. If you look at the breaker of these circuits on the house distro panel you will notice that they use two pole breakers. Each pole of the breaker is in a sense an independent 30A/120 volt circuit. That is, if you measure the voltage from each pole of the breaker to ground it will be 120 volts, and if you measure the voltage between the two poles of the breaker you will notice that it is 240 volts. The 120 volts of the two poles adds up to 240V because the 120V circuits are on opposing legs of the single phase electrical service of the house and are therefore additive. In residential settings, this is how higher voltages are supplied to household appliances like Dryers, Electric Ranges, Air Conditioners, Motors, etc. that require more power than can be reasonably supplied by a single 120V circuit. Where each pole of the breaker is in a sense an independent 30A/120 volt circuit, you can split them out in a distro system but only under limited situations.

 

The one situation where it is possible to use dryer plugs to power lights is when the dryer circuit is a four wire system (the receptacle has for slots: one for ground, one for neutral, and two for hot) and it is a single phase service. Where you can run into trouble is when the dryer circuit uses a three wire system (the receptacle has three slots: one for ground, and two for hot, and no neutral), or it is a three phase service. Many household and industrial 240V receptacles use a three wire system (no neutral) because they are meant to power single phase motors or heating elements that draw a perfectly balanced load and return no current because the single phase service legs are 180 degrees out of phase and cancel each other out – hence there is no need for a neutral return.

 

You run into trouble with this kind of circuit when you start to pull an unbalanced load on your distro system. And, where under most production situations you can never perfectly balance your lighting load, the two 120V circuits that make up this 240V circuit (as described above) will not have 100% phase cancellation and the extra current of the high leg will not have a safe return path.

 

The only way to pull power from three wire 240V circuits that meets code is to run your lighting load through a 240v-to-120v step down transformer. 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 circuit that is capable of powering bigger lights, like a 5k. What makes it safe to use a step town transformer with three wire 240V dryer/range/motor circuits is that the transformer automatically splits the load of whatever you plug into it evenly over the two legs of the 240V circuit. Where there is no high leg, the loads on each leg of the 240V circuit cancel out and there is no return that would require a separate neutral.

 

Use this link - http://ls.cinematography.net/read/messages?id=148478 - to a recent thread on CML on this same topic. 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

[James Martin]

Also this is assuming you are in America or Japan where the voltages are relatively similar (120 and 110 respectively). I don't know what houses are most commonly rated for in Europe but since they use a 220v system you'll need half as many amps for the same wattage. So Assuming they run on a 20 amp system as well you can plug in a 4k.

Just remember this VoltsxAmps=Wattage. (W/V=A is probably a more useful form of this equation)

 

Be extra careful with the higher voltages too.

 

Here in the UK a standard plug is 230V/240V (I believe it is supposed to be 230V, but some may still be 240). They are 13A maximum each, usually. That allows you approximately 3kw of draw. Houses can usually provide 32A of power as standard, but there are many exceptions and variations. One thing I should point out is that HMIs can draw more power on start-up than their rating. So, if there were such a thing as a 3K HMI it might not work in a socket that can theoretically provide 3.1K because it would trip the minute it asks for 3.2K.

 

Anyone with more experience than me on HMIs care to comment on that quirk of them? The rule I always got taught was turn the biggest lights on first...

[Guy Holt]

Hello,

I have a few questions about HMI's that have always made me curious.

 

1. What are the differences, pros/cons of magnetic vs. electric ballasts?

2. Being that brand new HMI's are so expensive, is there anywhere other than ebay that specializes in selling used HMI equipment?

3. Excuse my ignorance, does PAR mean you can plug the light in to an ordinary household circuit?

 

Electronic set their frequency internaly with their own xstal, so they can accept a wider spectrum of power conditions. Also with flicker free you have a little more freedom in frame rate/shutter speed without visible flickering presenting.

 

There are no “xstals” in electronic ballasts to set their frequency independent of line frequency. Electronic ballasts are “flicker free” at all camera rate/shutter speeds, not just “a little more” because they use capacitors to square off the power sine wave which causes an increase in the duration of the HMI arc so that the light is on more than it is off. Also called “square wave” ballasts or “constant power” ballasts, a light powered by an electronic HMI ballasts will put out 10% more light than the same light powered by a magnetic ballast, as well as be flicker free at all frame rates for this reason (the exception being extreme High Speed Cinematography). Electronic ballasts are also smaller and lighter than a magnetic ballast of the same wattage. The down side is that because of their sophisticated electronics electronic ballasts are more expensive and more fragile than magnetic ballasts.

 

As long as you shoot at one of the many safe frame rates, magnetic ballasts are also “flicker free” (where the topic of safe frame rates for magnetic ballasts is discussed extensively elsewhere in this forum I won’t get into it here.) Besides the extra bulk and weight of magnetic ballasts, the smaller magnetic ballasts (575-2500W) offer the distinct advantage of being less expensive and drawing less power (once they have come up to speed) than the commonly available electronic equivalents.

 

If you want to plug an 1.2kw HMI into a wall outlet, I would recommend you use a 1200w magnetic ballast. Operating at 120V, a 1.2kw HMI with non-power factor corrected electronic ballast will draw 18-19 amps verses the 13.5 amps of a magnetic ballast. Where the common household wall circuit is only rated for 15 amps, a 1.2kw Par with electronic ballasts will always trip the circuit breaker. Even if you can find a 20 Amp circuit breaker at your location, it will quite often trip it if there is something else, like a computer or light, on the same circuit. Where you can't always know, when you plug into a wall outlet, if it is a 20 or 15 Amp circuit and what else is on the same circuit, you are taking your chances when plugging a 1.2kw HMI with electronic ballasts into a wall outlet. 1200w electronic ballasts are only meant to be used on bigger budget film productions that distribute power from a generator and hence every circuit is 20 Amps and electricians can guard against overloading a circuit because they are distributing the power themselves.

 

A downside to magnetic ballasts when used with portable Honda generators is that you can’t load the generator to full capacity because you must leave “head room” for their higher front end striking load. When choosing HMIs to run off portable generators, bear in mind that a magnetic ballasts draws more current during the striking phase and then they “settle down” and require less power to maintain the HMI Arc. By contrast, an electronic ballasts “ramps up.” That is, its’ current draw gradually builds until it “tops off” - but it “tops off” with a considerably greater draw than a magnetic ballast “settles down” to.

 

Insufficient head room can be a problem when striking a 1200 Watt HMI on a Honda EU2000is, or on one of the 20A circuits of a EU3000is or EU6500is, when other thing are already plugged into the generator as well. Without an additional load on its 20A circuit, any one of the Honda EU series generators will power either an electronic or magnetic ballast. A magnetic ballast offers the slight advantage that you can power another tungsten or fluorescent light on the generator once the HMI has already struck.

 

While older HMIs with magnetic ballasts are less expensive to purchase or rent, there have been some very recent advances in HMI electronic ballast technology that make the newest ballasts worth the extra money when it comes to lighting with portable generators. For example the HMI ballast manufacturer Power to Light has introduced Power Factor Correction (PFC) into 1200 & 800 Watt ballasts. Previously only found in larger HMI ballasts, this advanced electronics reduces current spikes and harmonics in the power line and contributes to a more economical use of power than conventional electronic ballasts.

 

For example, the Power to Light PFC 1200W electronic ballast draws only 11 Amps verses the 18 Amps required by standard electronic ballasts and the 13.5 Amps required by magnetic ballasts after they have struck. And, like conventional electronic ballasts the Power to Light PFC 1200W electronic ballast “ramps up”, but it “tops off” with a considerably less draw than a magnetic ballast. Where a Kino Flo Parabeam 400 draws only 2 amps, that 8 Amp difference between using the new Power to Light PFC 1200W electronic ballast and a standard 1200W electronic ballast, can mean the difference of running four Parabeam 400s on a portable generator or not. I think you would have to agree that being able to run four Parabeam 400s on top of a 1200W HMI is a major boost in production capability.

 

In the interest of full disclosure, I should say that in addition to being a gaffer, I also own and operate a lighting company that rents and sells Power to Light ballasts. If it sounds like I’m hyping the P2L line it is not because we rent and sell them. We are also dealers for new and used Mole, Power Gems, and ARRI HMIs. As a professional Gaffer of a lot of tight budgeted historical documentaries for PBS’ American Experience and The History Channel (see my “credit-entials” on Imbd), I think these ballasts are a major development worth noting. For more detailed information on the advantages of using PFC ballasts (regardless of manufacturer) visit our website at : www.screenlightandgrip.com/html/hd_plug-n-play_pkg.html.

 

- Guy Holt, Gaffer, Owner/Operator of ScreenLight & Grip – a lighting and grip equipment rental, sales, and production service company in Boston.

[Guy Holt]

Magnetic ballasts set their running frequency against the cycles on the AC power coming in. If your power isn't exactly 50 or 60 hrz, you can have flickering on camera. Not a big problem on xstal sync gennys, but if you can only get a put put you need an electronic ballast.

 

I run a rental house in Boston by the name of ScreenLight and Grip and we rent and sell small portable generators for film production. The conventional wisdom regarding portable generators reflected in Michael Colliers comment went out the window with the recent development of inverter generators and power factor correction (PFC) in smaller (575-1200W) HMI ballasts. It is now possible to get 7500W of clean stable power in a single 120V circuit from a portable inverter generator without the use of crystal governors. And, unless your ballasts have power factor correction circuitry, electronic square wave ballasts are not necessarily the best for use with portable generators.

 

In the past, it was not possible to reliably operate more than a couple of 1200w HMIs on a portable generator. The primary factors limiting the use of HMIs on portable generators has been their inefficient use of power and the harmonic noise they throw back into the power stream. The adverse effects of the harmonic distortion generated by HMI ballasts (see power waveform below left), can take the form of overheating and failing production equipment, circuit breaker trips, overheating of the neutral wire, and instability of the generator voltage and frequency. Severe harmonic noise can also damage HD digital cinema production equipment, create ground loops, and create radio frequency (RF) interference.

 

 

If one knows how, it is possible to take advantage of recent technological advances in HMI ballast design and power generation, to create clean stable set power (like that in the power waveform above right) that is capable of reliably operating larger lights (HMIs up to 6kw or Quartz lights up to 5kw), or more smaller lights, off of portable gas generators than has ever been possible before.

 

For example, on a recent independent short shot on the Red, I used a modified Honda EU6500is Generator to power a lighting package that consisted of a 2.5kw, 1200, & 800 HMI Pars, a couple of Kino Flo ParaBeam 400s, a couple of ParaBeam 200s, and a Flat Head 80. Given the light sensitivity of the Red Camera, this was all the light we needed to light a large night exterior.

 

But, given the wide variety of generators manufactured, it is important to understand the benefits and drawbacks to each when it comes to their use in motion picture production. Especially, given that the increasing use of personal computers and microprocessor-controlled recording equipment in HD production has created an unprecedented demand for clean, reliable power on set at a time when the trend in lighting is toward light sources that can generate dirty power. For this reason, I have compiled a comprehensive survey of the prevalent lighting and portable power generation equipment. Tested how well they work together and I am making the results available in our on line newsletter. Where Harry Box, the author of the Set Lighting Technician’s Handbook is interested in incorporating this material in the 4th edition of the handbook I am making it available for peer review first.

 

I feel the need to make this material available prior to publication in the handbook because specific details of the inner workings of the latest portable power generation equipment is in short supply and harmonic noise has only recently become an issue. Why is harmonic distortion suddenly an issue in motion picture production? Because, the power generation and electrical distribution systems developed for motion picture production were never designed to deal with the abundance of non-linear loads like the electronic HMI and Fluorescent lighting ballasts so prevalent in production today. It’s a problem that has only recently begun because of the increasing use of these types of non-linear lighting loads. 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 are themselves sources of harmonic distortion.

 

In the past, attention was given to generator features such as automatic voltage regulation and speed regulation. But, given the rise in production problems associated with harmonic noise, an increasingly more important feature today is the quality of the generated power waveform and how well it interacts with today's light sources. For that reason, I did a series of tests that have resulted in oscilloscope shots of the power waveforms of different light sources on different portable generators. I have attempted to interpret the artifacts of harmonic distortion exhibited in these power waveforms, but where this is a relatively new issue, I welcome the input of other film/video production professionals so that the material can be as complete as possible for the handbook.

 

To see the results of my tests, use the link below to our website where I have posted my analysis of the compatibility of the latest lighting and portable power generation technology

 

www.screenlightandgrip.com/html/emailnewsletter_generators.html

 

I welcome any and all feed back.

 

- Guy Holt, Gaffer, ScreenLight & Grip, Boston