HMIs 120/220 questions

Patryk_Rebisz

Patryk_Rebisz

Veteran
In a few months i might embark on shooting a feature in 220v land (currently living in the States where 120v rule). Since i own a number of HMIs i though for the sake of savings i should just ship my lights to the location (since it's a 2 month long commitment). I know that with regular tungsten lights all i have to do is switch the bulbs for 220v versions but with HMIs... Is all i have to do is switch the electronic ballast from 120 to 220 and the rest (including the bulb) is fine???
 
Unless you're lucky enough to have a universal voltage (120 to 240VAC input), yes that's right. When a ballast of just about any kind is involved, the bulb is the same no matter what the input voltage.

You might be able to get away with a transformer as well on the input to change from 220VAC to 120VAC but that'd be a big transformer.
 
Well if you are shooting in a country running 50hz then you will get flicker running mains power unless you shoot in a PAL format frame rate to match the power, or run a US based genny running 60hz.
 
A question about 50 or 60hz boils down to two things really. 1). Will the ballast work at all on 50 or 60hz interchangeably if you solve the voltage level problem (a purely electronic issue). 2). What are the issues in film making and HMIs in 50hz or 60hz lands (frame rate / shutter speed interaction).

In my experience most ballasts, electronic or magnetic will still function on 50 or 60hz either way even if they were supposedly made for 120V 60hz and you run on a transformer in 50hz countries. But for either magnetic or electronic, to be safe, if you plan to run it on a conversion transformer, its best to ask the manufacturer about the "hz" interchangeability issue.

On electronic ballasts, from what I have seen looking at the "flicker mode settings", if they have a 50 or 60hz driving mode (to keep things as quiet as possible on set) that is completely decoupled from the power input "hz" and is produced internally so its independent of the line voltage. In other words, if you get the electronic ballast the power input it wants to be happy through transformer or whatever, it will still drive at whatever settings are available like 50, 60, flicker free, etc.

If its a magnetic ballast, the line voltage input "hz" directly sets the output driving frequency and therefore you have no choice and there are no flicker mode settings. But if the ballast is a 120V 60 hz and it can run through transformer on 50hz type voltage, it shouldn't be any problem for the ballast but rather back to #2 above and the shutter speed interaction concerns that go along with that.

The question of frame rate/shutter speed interaction is another one entirely and you can find information on that here for example:

http://www.cinemaelec.com/flickerfree_hmi.php
 
If you are lucky enough to have either an automatically switchable or manually switchable input voltage ballast, yes, that would take care of it. Either way, that would be known as universal voltage input and the frequency of input voltage would switch as well too.
 
Cool Lights said:
… On electronic ballasts, from what I have seen looking at the "flicker mode settings", if they have a 50 or 60hz driving mode (to keep things as quiet as possible on set)…
Click to expand...

I’m afraid Richard is confusing several issues. Whether the ballast is operating at 50 or 60hz has nothing to do with the “Silent Mode” that is provided “to keep things as quiet as possible on set.” Electronic ballasts are “flicker free” because they square off the power sine wave to the head, which causes an increase in the duration of the HMI arc so that the light is on more than it is off. Called “Square Wave” ballasts for this reason, a light powered by an electronic HMI ballast will put out 10% more light than the same light powered by the sine wave of a magnetic ballast. The down side to Square Wave ballasts is that the sharp angle of the power waveform as it starts to descend from its’ peak level causes the bulb quartz envelope to resonate. In the “Silent Mode” setting, the ballast rounds off the corners of the square wave to reduce the resonance. While still “Flicker Free” at most shutter speeds, you will see flicker at extremely high shutter speeds in “Silent Mode.”

For a detailed explanation of how HMIs operate see the companion website Harry Box has established for the Fourth Edition of “The Set Lighting Technician’s Handbook.” You can access the site, called “Box Book Extras,” with the password “set lighting.”

Mike Morgan
 
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