Automated Fixtures - Magnetic vs. Electronic Ballasts/power supplies

[TimMiller]

So what is the groups opinion of Magnetic vs electronic ballasts and other switching power supplies.

There are pro's and cons to both sides. Such as magnetic are much more heavy than electronic power supplies, but they are much more durable, and live much longer than electronic power supplies.

[derekleffew]

1. Tim, you seemed to have neglected the criterion that inspired the debate: electronic power supplies are usually auto-ranging regarding input voltage.
2. I don't necessarily agree with you that magnetic ballasts are more durable than electronic ones.
3. I seriously doubt I would ever specify a fixture due to its ballast either way. There are pros and cons to each, and very few fixture manufacturers offer the user a choice.
4. Which do the most popular fixtures: VL3x00, 2x00; MAC2000, 700; Showgun; Robe; Coemar; Elation; use?

[JD]

If the choice was which one would I want to power my heart/lung machine during an operation, I would chose magnetic hands down! Solid state ballasts, like switch-mode power supplies, live their lives 100 milliseconds away from death. Magnetic ballasts usually give you some fair warning they are getting cranky!

But, we are not talking heart/lung machines here, are we?


In a mover, I would chose electronic any day of the week. The voltage can be all over the place, and the little mos-fets just adjust their pulse width to compensate without blinking an eye (or bulb!) And then there is weight.... There is still a transformer core in an electronic ballast, however, it can be very small due to the frequency they run at. (Frequency and transformer core size are inverse proportional.) I'm just not a big fan of pumping iron being mixed with lighting!

[TimMiller]

Personally for one off i like electronic power supplies, for road stuff, and especially installs i spec magnetic. For an install, its one less thing that could go wrong, and its not like its going to be moved around a bunch.

[Radiant]

Forgive my ignorance, but what are the major benefits and liabilities of each design? From this thread, I gather that magnetic ballasts last longer. Yet I've also heard that they appear to flicker, especially when viewed by a video camera. When researching MAC 600s a while back, I noticed that the electronic ballast version can be operated at a variety of voltages, from 100 to 240 volts, whereas the magnetic ballast requires 208 volts (both figures denote 60 Hz.)

More to the heart of the matter, what does the ballast do?

[ship]

Just bought some LED PAR 20 lamps today and it said about them while not dimmable, and would switch off at a certain level implying either they dim or would work at full but at less than full voltage. But also, not to use them with electronic power supplies / dimmers. Confusing on that note but appairently they would get along better with magnetic. I know dimmable by any means Encapsulite fluorescent stick lights work with either type of control by way of magnetic ballasts by way of working a lot with the fixtures over the years and even using the parts to make some custom fixtures. You can dim say the fluorescent fixtures with a ETC rack without a problem and magnetic ballasts if quality are very simple to do.

On the other hand, electronic ballasts are perhaps more fogiving in not being sure but as opposed to needing full run up, than dimming down - while more perhaps stable the magnetic might be, the electronic ballasts might be more forgiving in startup and dimming minimum levels. Electronic dimmers and electronic ballasts would probably work better with each other than resistance dimmers with electronic ballasts.

[JD]

Originally Posted by Radiant

Forgive my ignorance, but what are the major benefits and liabilities of each design? More to the heart of the matter, what does the ballast do?

Ballasts are needed to regulate the current flow through the arc tube of discharge lights. In most cases, ballasts also provide the high voltage spike needed to ignite these lights as well.

Fast Overview:
Magnetic Ballast:
1) Large transformer-like core, power factoring capacitor, and a Igniter that produces a high voltage kick to get the light going.
2) Lamp actually "blinks" 120 times per second each time the voltage crosses 0 volts
3) Limited range of voltage and frequency input before unit can not provide the correct conditions to keep the lamp lit.
4) Very heavy
5) Simple design, so there is not much to fail. Been around for 60+ years, in almost every street light out there.

Electronic Ballast:
1) Converts AC to DC and then back to AC at a very high frequency using solid state components.
2) Fully regulated circuit can take very wide range of voltages and frequencies while maintaining proper lamp conditions.
3) Due to the high frequency, there is no visible lamp flicker.
4) Due to secondary frequency, the transformer core can be very small and lightweight.
5) Complicated design which "came of age" after high voltage transistors became available. (about 20 years)
6) Usually very reliable, but part failure will stop unit dead.

[TimMiller]

I think what really turns me off is that i have a pile of dead power supplies and lamp power supplies (aka electronic ballast). But I only have 1 or 2 dead transformers laying around, and they died due to crappy power.

[Radiant]

Thanks for the rundown JD!

Is the magnetic ballast "blink" perceptible to the human eye? What about to NTSC video cameras? I've heard that that it is, thus we selected electronic ballast units. But at 120 Hz, shouldn't that be so fast as to be imperceptible?

[JD]

Originally Posted by Radiant

Thanks for the rundown JD!

Is the magnetic ballast "blink" perceptible to the human eye? What about to NTSC video cameras? I've heard that that it is, thus we selected electronic ballast units. But at 120 Hz, shouldn't that be so fast as to be imperceptible?

Not too perceivable to the human eye, but to a TV camera (NTSC) which has a vertical rate of 59.94hz, a beat pattern which appears as a flicker can occur. There are some ways around this, such as using a low read rate from the CCD, but that has the same effect as a slow shutter (in fact, some refer to it as the shutter speed) in that you will end up with blur on fast moving objects. Unlike analog cameras, where the vertical read rate is fixed at the sync gen's vertical frequency, digital cameras can read the CCD at any rate, and the output only becomes fixed at the NTSC encoder, so they usually do not have a problem that cannot be worked around.

Same kind of effect as someone trying to film a TV monitor with an older analog camera, or too high a shutter speed.

EDIT: Generally, if the lamps are young, there is a bit of persistence in the glowing of the arc gas and you may not notice any flicker. As the lamps get old, they get a bit like old florescent lamps where there is a distinct "black" period in the ac cycle and it will be more problematic to the camera. Solid state ballasts generally output at 40khz to 300khz dependant on the application and load/line conditions. Because of that, there is no perceived flicker outside of what may be caused by debris in the arc tube.