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generator for a 4kw light


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#1 Brandon Rubesh

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Posted 05 May 2008 - 10:59 AM

Hello,
I'm shooting a short next week and will be using a 4kw HMI. As far as generators goes, the producer of the shoot is trying to find a way to rent one cheaply and it was a thought to get a 6Kw monophase generator from a construction rental place. I've been told that it would work fine with an HMI as long as the ballast is electronic and not magnetic. Just wanted to post this to see if anyone else has done this before or if I'm making a grave mistake. It can be a bit difficult to get information where I am... As I'm in France and do not speak french.


Thanks for any info - Brandon
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#2 Matt Workman

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Posted 05 May 2008 - 12:22 PM

I've seen LTM/Arri 4K Pars powered from an adapted Honda 6500k genie. Definitely need to be electronic, also the right voltage as the lamp seeing that you are in France.

I don't know about "construction" generators...that just doesn't sound good to me.
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#3 Saul Rodgar

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Posted 05 May 2008 - 05:59 PM

I've seen LTM/Arri 4K Pars powered from an adapted Honda 6500k genie. Definitely need to be electronic, also the right voltage as the lamp seeing that you are in France.

I don't know about "construction" generators...that just doesn't sound good to me.


Yeah, I have heard horror stories regarding cheap construction genies that don't keep sync regardless of whether you have a magnetic or electronic ballast. There are so many different kinds and contruction workers don't need them to keep sync ! . . I hear the inverter in the generator is what makes the output flickerless. I am not an electrician so I can't tell you what type of inverter you need in the genie, and it also has to be able to handle at least 50 amps for that 4k light to work.

If you are shooting HD, you will find out right away if it works or not. With film it could be disastrously late by the time you can tell if it's flickering or not.

I am sure there are some people here who can answer this better than me.

I would just stick with what will work, even if it means paying more for the damned thing . . .
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#4 timHealy

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Posted 05 May 2008 - 08:26 PM

A non crystal generator should work with an electronic ballast and many on this site have said they have done so.

But the inverter has nothing to do with that. And inverter is a device that usually converts battery power to usable AC.

A crystal sync governor controls the hertz and AC output to make a generator usable for film and TV.

Best

Tim
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#5 Saul Rodgar

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Posted 06 May 2008 - 11:22 PM

But the inverter has nothing to do with that. And inverter is a device that usually converts battery power to usable AC.


That is inaccurate. An electrical inverter converts DC current to AC current. Genies generate DC power mostly. Big lights usually run on DC power, smaller lights plug to edison outlet, that is AC current. So the problem may not the inverter as I claimed, but Tim's explanation isn't solving the problem either.

http://en.wikipedia....er_(electrical)

Again, I am not an electrician. But short of doing my own test, or being present at someone else's and then watching the footage, I will only take the word of a certified electrician/ experienced DP that using an off-the-shelf (off-the- lot?) construction genie will work.

Any certified electrician/ experienced DP out there who can put us out of the misinformation?

Edited by Saul Rodgar, 06 May 2008 - 11:25 PM.

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#6 JD Hartman

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Posted 07 May 2008 - 02:01 PM

That is inaccurate. An electrical inverter converts DC current to AC current. Genies generate DC power mostly. Big lights usually run on DC power, smaller lights plug to edison outlet, that is AC current. So the problem may not the inverter as I claimed, but Tim's explanation isn't solving the problem either.


I'm not even going to try and strighten out this confuion. I will say that the small (1000 to 5000w) inverter generators produce DC and invert it to AC, but larger (10,000 watt) generators produce primarily AC. They don't have an inverter in them. The only DC produced is is to charge the battery and for the exciter circuit. They are actually motor driven alternators, not "generators".
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#7 Saul Rodgar

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Posted 07 May 2008 - 06:50 PM

. . .

Edited by Saul Rodgar, 07 May 2008 - 06:55 PM.

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#8 timHealy

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Posted 07 May 2008 - 07:03 PM

Sorry about whatever confusion I added. I should have simply said an inverter turns DC into AC. Most of my experience is with larger 500 to 1400 amp capacity generators which produce AC directly. And like a car engine has an alternator to keep it's battery up to charge as JD described.

But it is the crystal sync governor that controls the hertz (or frequency). For 24 fps, a governor keeps the hertz between 59.75 to 60.25 for lighting needs in the U.S. So lights with a magnetic ballast will be in sync with a film camera.

A generator such as an EU 2000 or a "construction" generator that doesn't have crystal controlled governor will need an electronic ballast to cover yourself so that it will be OK for 24 fps shooting.

I know some people who have used small HMI's with magnetic ballasts powered by an EU 2000 or 3000. Here is a photo from I Am Legend with a car rigged with an EU 3000 powering an LTM 1200 watt par.


IMG_8193.jpg

But if you don't agree then feel free to do your own tests.

Just for clarification big lights don't usually run on DC power.
There was a time when they did. But that was a long time ago when Carbon Arcs and Brutes were the big lights of the day. Today most lights, big and small run off AC, regardless of their plugs. All HMI's run off AC and while Tungsten can run off either AC or DC, it is very rare to see DC on a film set today unless there is a special need.

Best

Tim

Edited by timHealy, 07 May 2008 - 07:07 PM.

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#9 Saul Rodgar

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Posted 07 May 2008 - 10:22 PM

Cool, thanks for the clarification!

S
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