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#1 Alberto Larios-Saavedra

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Posted 27 July 2007 - 10:07 PM

Does anybody know if I can use a portable generator (a 6k) to power a 1.2 HMI light? The generator would be rented from one of those places for do-it-yourself home projects and I would only hook the one HMI light, nothing else. Would I have any flickering issues?

Thanks,
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#2 Nathan Blair

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Posted 27 July 2007 - 11:40 PM

From what I've been told, HMI lights require a very steady frequency of electricity running to them, and normal generators create a frequency that sometimes varies because of the way they run. If you're using a ballast with your HMI, a bad frequency could eventually damage your equipment.

There are special generators for these jobs which are known as "Crystal Sync" generators. They will give that steady output of electricity and you wont have flicker problems.

The cheapest model crystal sync generator I've found, which most rental houses own, is the Honda 6500W.

Usually it runs at around $125 a day.

Good luck,
Nate
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#3 Alberto Larios-Saavedra

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Posted 28 July 2007 - 12:59 AM

From what I've been told, HMI lights require a very steady frequency of electricity running to them, and normal generators create a frequency that sometimes varies because of the way they run. If you're using a ballast with your HMI, a bad frequency could eventually damage your equipment.

There are special generators for these jobs which are known as "Crystal Sync" generators. They will give that steady output of electricity and you wont have flicker problems.

The cheapest model crystal sync generator I've found, which most rental houses own, is the Honda 6500W.

Usually it runs at around $125 a day.

Good luck,
Nate


Thanks Nate.
Do you know if I can use a baby tungsten? Not the same output but it still would help a little bit.

Thanks,
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#4 chris kempinski

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Posted 28 July 2007 - 11:46 AM

Alberto,

Honda gennie's are great! We run a 1200 on the 2K's all the time with no problem at all. You will need an electronic ballast, and set it to square wave when you use the light. The electronics can handle the varied voltage the a smaller generator puts out and will compensate and keep the light running. If you use a magnetic ballast the light may not strike, or may turn off due to voltage drop.
Another trick is to use a transformer, but that's another thread all together.

oh and tungsten is always flicker free.

good luck
Chris
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#5 Ralph Keyser

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Posted 01 August 2007 - 03:02 PM

I've had very good luck with the Honda 2000ei generators. They are actually DC generators that use an inverter to get the AC that they output, so the output volatage and frequency are very stable (much more so than the typical construction site gennie) and they are surprisingly quiet generators. You'll still need to locate them away from set and do a little baffling to get usable dialog in a quiet location, but it is definately doable. They will handle a single 1.2K HMI unit with no trouble, and I've had good luck even with magnetic ballasts although the electronic ballasts should be more stable.
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#6 Phil Savoie

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Posted 01 August 2007 - 03:35 PM

I second the Honda. Very quiet and reliable. Just what you need.
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#7 Bill Totolo

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Posted 05 August 2007 - 05:32 AM

Can the Honda 6500 Crystal Sync 50 Amp genny handle a 4K HMI fresnel w/ electronic ballast?
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#8 robert duke

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Posted 05 August 2007 - 11:18 AM

Can the Honda 6500 Crystal Sync 50 Amp genny handle a 4K HMI fresnel w/ electronic ballast? yes


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#9 Alessandro Machi

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Posted 05 August 2007 - 02:42 PM

There are two reasons to get the generator a bit further away from the actual shooting location, one is to cut down the sound, and other is to keep the exhaust away from the actors and crew. You can lose up to 20% of the power output if the outside temperature drives up the operating temperature of the genny from what it is normally rated at.

Once you get over 85-90 degrees farenheit you will begin to lose some of the power output of the genny unless you are able to keep it in shade. I don't know the exact drop off as it relates to higher temperature.

That's all I know about gennies. :rolleyes:

Oh yeah, make sure the exhaust output of the genny is pointed away from the shoot location and not pointed at any other living things or businesses. Safely elevating a generator, or using one that has an elevated exhaust that extends up 8-10 feet is a good way to help disperse the global warming you are contributing to the world. (the global warming comment was a joke).
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#10 Alessandro Machi

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Posted 05 August 2007 - 02:54 PM

If you're using a ballast with your HMI, a bad frequency could eventually damage your equipment.

Good luck,
Nate


Do you mean that anything else that is hooked up to the same generator can get damaged, or did you mean the bulb itself could get damaged, or both?
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#11 Rob van Gelder

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Posted 09 August 2007 - 11:42 AM

Check the electronic ballast, if it has a Power Factor Correction or not.
If the Cos Phi is lower than 0.9 than be prepared for an increase of real power that the lamp needs.
For instance,a 4Kw HMI from Arri with electronic ballast without PFC (or ALF as Arri names it) will use around 40% more power and this is
6000 watt, definitely the limit for your generator in question.
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#12 edward read

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Posted 12 August 2007 - 11:32 AM

[From what I've been told, HMI lights require a very steady frequency of electricity running to them, and normal generators create a frequency that sometimes varies because of the way they run. If you're using a ballast with your HMI, a bad frequency could eventually damage your equipment.]

Not quite true. The frequencey question and generators has only to due with an interaction between the shutter of a camera and the frequency of the light - nominally 60hz (60 times per sec.) An HMI is an arc light where the arc is being generated 60 times a second. There are "flicker free" shooting speeds that put the same number of arcs on every frame of film. When there are sequential frames that have different amounts of arc flashes on them, say the frequency was 59 hz, we percieve that as hmi "flutter" - the frames get lighter and darker - it sort of looks like blinking flash frames. Running an HMI on a non crystal synced generator can cause this if the hmi is set to silent mode or has a magnetic ballast. When an HMI is set to flicker free (electronic ballast only) then the ac sine wave is squared off - the top is electronically cut and the duration of the arc is extended to prevent hmi flutter. Its an electronic way of simulating "thermal inertia" - the decay of a filimant as it cools from full to off. Its this thermal inertia that keeps a tungsten unit from fluttering. The filiment is still being flashed 60 times a second but the filiment is still glowing hot between the flashes and doesn't perceptivaly dim.

If the electricity coming from a generator isn't within the operating perameters of the HMI it won't strike. Most HMI's these days have electronic ballasts. An easy way to tell is if you can pick it up with one hand easily. Elecronic ballasts are light - magnetic ballasts are extremely heavey. a 4k magnetic ballast takes 2 men to lift.

Flicker free should also be used with 24 frame video.
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