HMI's and Power inverters

Michael Collier · June 12, 2007

I am prepping a shoot comming up this sumer. Problem is we have nothing but daylight these days. The sun doesn't go down until 10-11 and the sky remains bright until the sun rises again at around 2 or 3 am. I want to shoot during this period of magic hour for a dusk feel.

I want to get contrast up but in that environment, I have little options. If I feel I can use it, the producers have let me put a few HMIs on there, but theres no chance of a crystal synced generator. Is it possible to drive an HMI off an inverter hooked up to a car engine?

I understand the timing might not be perfect, but we are shooting video (digibeta, DVW-700WS), so flicker should be less of a problem. On their website they say the ballasts are 'flicker free' ballasts. I assume this means they are electronic and can accept a wider range of power before they begin to flicker?

It would be great if we can, I might be able to get 2 or 3 HMIs, which would be a godsend in this environment. I want the dark blue of the sky, but I need that backlight to sell the image. Please tell me this will work, or let me know what I need to make it work (lots of stingers ran several blocks from freindly businesses? hmmm.) Otherwise my only option is to go the oposite route and put black grifflon in a frame as negative fill....not really what I want when the whole image will be on the dark side...I need more backlight. Its my cowbell for this film.

Stuart Brereton · June 12, 2007

Car batteries are not designed to supply current over long periods of time. Their job is to give an huge surge of current to the starter motor, then leave the job to the alternator once the car is running. The alternator only runs whe the engine does, and although it powers everything electrical in the car, it's fairly easy to overload them, and that's a fairly expensive fix.

You need to get hold of some heavy duty leisure batteries, at least 100amp/hr, and then some good inverters, like these - ebay item 330115837949.

Inverters can be picked up very cheaply if all you need is 300w, but even for something like a .575kw hmi, you're going to need at least a 1kw inverter. Remember, HMIs take a large power spike to get them going, so you need to make sure your inverter can take it.

Hope this helps.

Michael Collier · June 12, 2007

Yeah, I don't know what sort of alternator the car I have in mind has. I know some aftermarket alts can supply 140amp+ (at 12v thats around 1600w) and I could leave the car running, but it sounds like it might be cheaper just to rent a small generator (2-5k) for the weekend. The problem is this is not a film community and there is only one crystal synced generator in town, and its way too expensive for this film.

can I run an HMI off an unsynced motor, if the ballast is a flicker free ballast?

Armando Castro · June 12, 2007

We had a car shoot a few weeks ago in which we tried rigging a 400w joker on a 1kw inverter and it didn't work...the light simply wouldn't strike. Luckily, we had some battery belt packs as a backup. You might want to look into battery packs for this. A slimverter with a 30v battery pack will work great!

Armando Castro · June 12, 2007

We had a car shoot a few weeks ago in which we tried rigging a 400w joker on a 1kw inverter and it didn't work...the light simply wouldn't strike. Luckily, we had some battery belt packs as a backup. You might want to look into battery packs for this. A slimverter with a 30v battery pack will work great!

Some pics.......

edward read · June 13, 2007

can I run an HMI off an unsynced motor, if the ballast is a flicker free ballast?

yes

terry kim · June 21, 2007

I am prepping a shoot comming up this sumer. Problem is we have nothing but daylight these days. The sun doesn't go down until 10-11 and the sky remains bright until the sun rises again at around 2 or 3 am. I want to shoot during this period of magic hour for a dusk feel.

I want to get contrast up but in that environment, I have little options. If I feel I can use it, the producers have let me put a few HMIs on there, but theres no chance of a crystal synced generator. Is it possible to drive an HMI off an inverter hooked up to a car engine?

I understand the timing might not be perfect, but we are shooting video (digibeta, DVW-700WS), so flicker should be less of a problem. On their website they say the ballasts are 'flicker free' ballasts. I assume this means they are electronic and can accept a wider range of power before they begin to flicker?

It would be great if we can, I might be able to get 2 or 3 HMIs, which would be a godsend in this environment. I want the dark blue of the sky, but I need that backlight to sell the image. Please tell me this will work, or let me know what I need to make it work (lots of stingers ran several blocks from freindly businesses? hmmm.) Otherwise my only option is to go the oposite route and put black grifflon in a frame as negative fill....not really what I want when the whole image will be on the dark side...I need more backlight. Its my cowbell for this film.

terry kim · June 21, 2007

hey mike

to answer

inverter w/ deep cycle batteries may be the solution but a brand new inverter is about $1000 per 1k and batteries are heavy, prone to temp and environment and takes a long time to charge..... but good if there is nothiing else

digibeta ... w flicker free ballast. electronic ballast mean that you can shoot off frame and PAL settings etc without the concern of the power source affecting your light source. flicker free + electronic = shoot freely

have you looked into a 2k honda portable generator? or even beter a 5500w honda generator w/ a transformer? then you don't need a larger CS gen set or messy inverter battery deals. i'm sure that alaska has an abundance of portable generators!

dark blue sky .... like a day for night ? or polarizer or a mattebox full of graduated filters or in post "magic windows" program or FCP 5.1.4 HD studio w/ motion? color?

good luck

Michael Collier · June 21, 2007

Yes, I am looking at the honda gennys now. I think I might end up renting. And you would be correct, there is a great abbundance of gennerators in town...just few crystal sync. I am glad to find out I can run the HMIs off those, given their flicker free ballasts.

And no, its not a true day for night. Its an Alaskan sumer night for Alaskan sumer night. There is something very eerie and odd about being up at 12am and still having light in the sky. The light is very soft but still directional, since the sun basicly hangs just below the horizon line for 4 or 5 hours. Its hard to describe but its my favorite lighting pattern we have up here. If the clouds are just right, its an amazing thing to see. I just want to capture that feeling for the last scene.

In other news I bought a few hundred white LEDs, gutted a broken omni light and plan to make a small soft light for our car scenes. I even figured out how to make each button press decrease the light by exactly 1/3 stop. I think its fair to say I am looking forward to this shoot. I may even get to fly a steadycam on it!