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#1 Evan Andrew John Prosofsky

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Posted 28 November 2008 - 01:36 PM

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!
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#2 Chris Keth

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Posted 28 November 2008 - 01:59 PM

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.
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#3 Evan Andrew John Prosofsky

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Posted 28 November 2008 - 02:03 PM

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
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#4 Michael Collier

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Posted 28 November 2008 - 02:04 PM

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.
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#5 Chris Keth

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Posted 28 November 2008 - 09:43 PM

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.
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#6 David Mullen ASC

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Posted 28 November 2008 - 10:05 PM

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.
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#7 Evan Pierre

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Posted 28 November 2008 - 11:24 PM

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 by Evan Pierre, 28 November 2008 - 11:26 PM.

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#8 Rob Vogt

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Posted 29 November 2008 - 05:36 AM

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 by Rob Vogt, 29 November 2008 - 05:38 AM.

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#9 Simon Wyss

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Posted 29 November 2008 - 07:10 AM

As of today we have 235 Volt nominal in the mains, through the day around 233 V.
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#10 Evan Andrew John Prosofsky

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Posted 29 November 2008 - 03:00 PM

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.
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#11 timHealy

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Posted 29 November 2008 - 07:06 PM

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
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#12 Robin R Probyn

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Posted 30 November 2008 - 03:24 AM

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 !
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#13 Rob Vogt

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Posted 30 November 2008 - 05:50 AM

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
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#14 Damien Bhatti

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Posted 03 December 2008 - 03:41 PM

Is there any alternative for flicker free lighting, than the expensive HMI route?
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#15 Ralph Keyser

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Posted 03 December 2008 - 05:15 PM

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.
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#16 JD Hartman

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Posted 04 December 2008 - 06:20 PM

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).
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#17 Damien Bhatti

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Posted 05 December 2008 - 11:37 AM

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?
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#18 Rob van Gelder

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Posted 06 December 2008 - 10:17 AM

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

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Posted 21 January 2009 - 12:10 PM

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.cinematogr...ages?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
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#20 James Martin

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Posted 21 January 2009 - 02:27 PM

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...
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