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More questions about HMIs


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#1 altered ego

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Posted 31 January 2009 - 04:58 AM

A few questions about HMIs, specifically dealing with flicker:
- with magnetic ballasts flicker can be a problem if the source is operating outside of 60 hrz if the genny isn't crystal controlled. How do you measure, monitor and regulate the hrz to avoid the flicker? Is this a control function on the genny itself or there another method? Do you need a tool to measure the hrz?

- If you are drawing power not from a genny but from the power mains, i.e. tie-in or direct plug in, is flicker still a problem or does that power source automatically run at 60 hrz?

- Do any HMIs run on DC or all they all AC operated? And if so, in the rare event that your power source was DC but you needed to run HMIs, how would you do it? Would a rectifier work or would you need something else?
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#2 Stuart Brereton

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Posted 31 January 2009 - 08:06 AM

Hi,

You need to go to My Controls and change your display name to your real name, as required by forum rules.
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#3 timHealy

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Posted 31 January 2009 - 11:36 AM

A few questions about HMIs, specifically dealing with flicker:
- with magnetic ballasts flicker can be a problem if the source is operating outside of 60 hrz if the genny isn't crystal controlled. How do you measure, monitor and regulate the hrz to avoid the flicker? Is this a control function on the genny itself or there another method? Do you need a tool to measure the hrz?

- If you are drawing power not from a genny but from the power mains, i.e. tie-in or direct plug in, is flicker still a problem or does that power source automatically run at 60 hrz?

- Do any HMIs run on DC or all they all AC operated? And if so, in the rare event that your power source was DC but you needed to run HMIs, how would you do it? Would a rectifier work or would you need something else?


controlling hertz is part of the governor and the generator. No way to do that outside the genny.

There are meters to read hertz.

hertz is controlled form the local utility if using ties in's. you cant change it.

HMI's run on AC only. Brute arcs can run on AC with a rectifier. I have never seen any sort of DC to AC rectifier in the film business. Everything is AC these days unless you are shooting at an old stage with DC somewhere. Some generators can do AC or DC.

If you have access to DC you can use Tungsten. They run on both AC and DC with no flicker issues unless you are doing some really high speed photography. I have never experienced it but I believe some people here have experienced flicker on small tungsten lamps say 5k and under, but that needs to be confirmed.

Best

Tim
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#4 Michael Collier

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Posted 02 February 2009 - 06:56 PM

Ditto what stuart says - its forum policy to use real names.

smaller HMIs come with optional DC/AC balasts that can plug into mains, battery or DC source, like the joker 200, 400, 800.

A rectifier (4 diodes in a full bridge configuration, usually with smoothing capacitors) can only change AC-DC, and are not able to change volts while doing this (apart from the voltage loss across the diode).

If you have DC power and need AC, you need an inverter. Inverters are much more design and part intensive and so cost much more. Add to that its hard to find one over 1000w (sometimes hard to find one over 500w) and they are not too efficient at what they do. If you have batteries see if the jokers would work. Otherwise get a genny.

If you run DC to tungsten you need to find globes that are rated for that voltage. If you run a 120vac globe on 30vdc, it will be dim and orange, just like you had a squeezer on it. Its also not good for the life of the globe.
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#5 Guy Holt

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Posted 02 February 2009 - 07:01 PM

Do any HMIs run on DC or all they all AC operated? And if so, in the rare event that your power source was DC but you needed to run HMIs, how would you do it? Would a rectifier work or would you need something else?


The smaller HMIs (125-200W) will run on DC with a special DC ballast designed to run them off battery belts. All larger HMIs run on AC but can be powered by DC sources with an inverter. Larger HMIs (400-1200W) can be run on what are called “Battverters”. A “BattVerter” is a Battery/Inverter system designed to provide AC power from DC Batteries - usually for traveling car shots. I quite often use “Battverters” to power 1200HMIs for a little Daylite fill for street interviews. Your area rental house might have the Kino Flo system. We offer a variety of BattVerters - from a compact turnkey 750W BattVerter to the 1800W battery/inverter rig we custom built to power four 4’ – 4 Bank Kino Flo Fixtures on an Airport Shuttle for the feature film “Shuttle” (use the link below for more details).

You can get everything you need to build a battverter at your local marine supply store. You need a DC power source (deep cycle Marine Cells work best), a DC-to–AC True Sine Wave Power Inverter, and a Battery Charger (to top off the charge on the batteries between takes). Wire these components into an equipment case and you can put it on the floor of the back seats or in the trunk of the car. If you plan to power larger HMIs (400-1200W) I would suggest making up a lightweight "jumper cable" that you can securely attach to the leads of a car's battery. That way you can run the engine and the alternator will charge the batteries as they are being discharged by the lights. A Battverter will enable you to use a car as a generator. Use the engine to run the lights through the Battverter as described above during set up and rehearsals. When it comes time to shoot a take, simply shut off the engine and continue to run the lights on the BattVerter alone. Running the vehicle engine between takes charges the batteries so that they will run lights all day or night.

To see how to build a Battverter, use the link below for a more elaborate Battverter system that we built to run four 4' 4 bank Kinos to light a shuttle bus for the upcoming feature "Shuttle" that was shot here in Boston on the Viper. The production stills show you pretty much how we wired it into the shuttle bus.

http://www.screenlig...lmstrip4lg.html

Word of caution: charging batteries generate Hydrogen gas. Do not use a Battverter in charging mode inside a tightly sealed car. Put the Battverter in the trunk, or rig it to the front bumper (as pictured in the “Shuttle” production stills), if you are going to use the engine to charge it while shooting.

Guy Holt, ScreenLight & Grip, Rigging Gaffer on “Shuttle”
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#6 Andy Barnett

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Posted 06 February 2009 - 11:55 AM

A few questions about HMIs, specifically dealing with flicker:
- with magnetic ballasts flicker can be a problem if the source is operating outside of 60 hrz if the genny isn't crystal controlled. How do you measure, monitor and regulate the hrz to avoid the flicker? Is this a control function on the genny itself or there another method? Do you need a tool to measure the hrz?

- If you are drawing power not from a genny but from the power mains, i.e. tie-in or direct plug in, is flicker still a problem or does that power source automatically run at 60 hrz?

- Do any HMIs run on DC or all they all AC operated? And if so, in the rare event that your power source was DC but you needed to run HMIs, how would you do it? Would a rectifier work or would you need something else?



Hi
Flicker is to do with the combination of shutter speed and mains frequency. I'm assuming you're shooting at 24fps. 60Hz 24fps is a 'safe' combination. If a non-crystal supply is used, the camera can be synchronised to the mains in various ways (talk to the camera rental people). Alternatively you could use electronic ballasts which produce an output independant of supply frequency.

Mains frequency should be reasonably reliable in US, Europe but not in some countries. A magnetic ballast will run at the frequency of the supply. Only electronic ballasts can run independantly of the mains frequency.

Some electronic ballasts up to 1200W can run on DC but they convert it internally to AC. Also, electronic 'inverters' convert DC to AC but only high quality 'true sine wave' ones should be used. Units of a few hundred watts are readily available (eg for caravans) but higher power units would be very expensive.

Hope this helps

Andy Barnett
ARRI GB
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Visual Products

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Media Blackout - Custom Cables and AKS

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Aerial Filmworks

Glidecam

Tai Audio

CineTape

rebotnix Technologies

CineLab

Ritter Battery

Abel Cine

Willys Widgets