HMI's

[Guest Christopher Wedding]

Hey I'm getting ready to lease some equipment and I've heard a few conflicting remarks about the two types of ballasts for Arrisuns. I've heard the electronic ballasts, although much lighter, are more 'finicky' about power source. Then I heard that magnetic ones might not be flicker free, which I don't believe. On the same note, what about other brands, are there any others that definetly are or are not flicker free...ala Ebay HMI's like SunRays?

 

Thanks for the help.

 

Chris

[oscar jimenez]

Ok, HMI Lamps depending wether magnetic or electronic ballast, may be FF ( flicker free ) or not. Electronic Ballasts usuallly can be used ( they do have a selector, at least Arri's) that can be set at 24/25 fps and FF mode. There are certain Camera Speeds and Shutter angles that are flicker free speeds, see American cinematographer manual, David Samuelson's Cinematographer's Hand Book or visit www.cinematographyelectronics.com Electronic Ballast are more expensive, yet they are lighter in weight than magnetic ballast, difference is the coils inside magnetic ballast. This doesn't mean that Magnetic Ballast are anymore Sturdy than Electronic Ballast, some magnetic ballasts have the coil built and arranged vertically, which is somewhat delicate, having in mind center of gravity of things. There are many brand of HMI's Lamp/Heads and Ballasts, this doesn't means that they are or not FF it depends wether the ballast is electronic or magnetic. Being electronic "flats" wave frequency peaks and valleys making it more "flatliner" so reduces flicker at max. On magnetic ballats, you have to play with Flicker Safe Speeds + combination of Shutter angle degree.

Hope I have been helpful.

[timHealy]

Personally I love the Arri line of HMI Pars. They all have the same basic design from the smaller 575w up to 12k's, and you can use the heat of a par or toss in a fresnel lamp and use them direct. All their heads will work on magnetic ballasts which are not flicker free or electronic flicker free ballasts. I have never seen a magnetic flicker free ballast. Some flicker free electronic ballasts may have trouble on some generators. I am not sure why but the black leg on many three phase generators is not regulated. Someone who has an electronic/generator background would have much to add here about why this is. But having run into this trouble from time to time, just switching legs may more than likely take care of the problem when it does occur. I seem to recall a job once where the red leg had been the culprit too??? So when in doubt, switch legs.

 

long cable runs may have an adverse affect on HMI's. long runs equals more resistance. If you strike on HMI and another goes out, it is a sure sign of a voltage drop. Crank the voltage up on the genny or bring it closer. And I hope the electrics ran 4 ought first if it was a long run. Some electrics run a double pump run for longs runs or at least a double neutral for the weird harmonic effects of many electronic ballasts.

 

just my 2 cents.

[timHealy]

Just an update

 

I spoke to a friend who works with generators and thinks the unregulated black leg is a myth. Though it is true that the black leg of a generator seems to cause trouble for some HMI's it is for a different reason. He thinks it is more the effect of the electric supply for the brains of the generator. The brains control the electric output of the generator but also controls the same electric that feeds itself. Then throw in the weird harmonic effects of a few square wave ballasts and sooner of later one doesn't fire. The resolution is still the same: Switch phases.

 

Tim

[Gilbert]

Hey I'm getting ready to lease some equipment and I've heard a few conflicting remarks about the two types of ballasts for Arrisuns.  I've heard the electronic ballasts, although much lighter, are more 'finicky' about power source.  Then I heard that magnetic ones might not be flicker free, which I don't believe.  On the same note, what about other brands, are there any others that definetly are or are not flicker free...ala Ebay HMI's like SunRays?

 

Thanks for the help.

 

Chris

<{POST_SNAPBACK}>

 

A magnetic ballast is not a flicker free ballast, an electronic ballast is a flicker free ballast, Arrisun or not.

 

Regarding "finicky", an electronic ballast is more sensitive but just as reliable as long as you take the time, before you start using it, to check the power source, head feeder, head & globe.

 

Remember: "A magnetic ballast is a tank but an electronic ballast is a BMW." -GN-

 

I hope this helps.