Electronic Ballasts

[Chris Hinds]

Forgive a Soundie trying to learn a little about lighting, but I've been told that an electronic ballast such as that fitted to a Mac 700 is preferable to a conventional system as used in the Mac 500 for Television work. I understand that with the new optics a Mac 700 would be brighter, but why would an electronic ballast be preferred for use on television?

 

Thanks

 

Chris

[Whiteout]

I think this has something to do with noise - won't the ballast make the fixture quieter?

[Nick S]

Conventional ballast is at 50-60Hz, depending on your mains supply. You can run into issues with flicker when working with video or high frame rates for film. Electronic ballast is flicker free.

[zonino]

with a magnetic (conventional) ballast the voltage across the lamp alternates at the rate of the electrics supply, so 50-60Hz. the human eye can't see this, however, television cameras take frames in the same region as this, so they do "see" the flicker.

 

an electronic ballast still flickers, only this time its 20,000hz! which the cameras don't "see" this,

 

so they 700's, which all have electronic ballasts, are preferential to the 500's which dont, you can however get the 500E & 600E which do have electronic ballasts, but do cost about £1000 more!

 

hope that makes sense!

[BlueShift]

I believe the comment about noise is also true, I was under the impression that the Mac 600e, for example, is quieter than a 600. Whether this is directly connected to the change in ballast or whether its just something the revised when adding the 600e to the line im not entirely sure...

[MarcT]

Not only that - a magnetic ballast can be significantly heavier than the equivalent electronic ballast because hefty transformers and inductors (ie lots of iron) are needed for 50-60Hz mains frequencies. The higher frequencies used in electronic ballasts require physically smaller inductive components.

 

Sometimes you can see the flicker on moving lights with magnetic ballasts. In a big rig there's usually at least one with noticable flicker...

[Nick S]

Whether this is directly connected to the change in ballast or whether its just something the revised when adding the 600e to the line im not entirely sure...

 

I know the Mac 700, unlike the 500, has various temperature sensors that feedback and control the fan, meaning you should in theory get less fan noise (in addition to the noise reduction from the ballast).

[mattwright15]

Noise Reduction has nothing todo with a electroinic ballast, all the components of the mac 500/600 and 500/600e are the same except the ballast- and relevent other electronic components on the PCB todo with the type of ballast the unit is running from.

Noise in moving lights is caused by the Fans in the units normally, unless there is a fault somewhere else causing another component to creat a un wanted noise

 

Matt

[Tomo]

There are three main advantages to electronic ballasts:

 

1) Weight. Electronic ballasts are much lighter than magnetic.

2) The power harmonics and power factor are usually kinder to the supply.

3) Higher drive frequency. How high depends on which one you've got.

 

Of these, 1 is the most significant.

The other two are nice, but most of the time you'll never notice.

 

Incidentally, if the ballast is noisy then it's probably breaking down.

A magnetic ballast should be almost silent - there's a slight hum, but you probably won't hear it over the fans.

Louder noise is created when the iron laminations start to come unglued, so it starts to rattle.

 

If ignored, it will eventually fail. Failure modes range from simply cutting the coil so the lamp fails and cannot be restruck, to physical shattering of the inductor.

The latter isn't very likely though.