Is it possible to build your own Metal Halide Ballast?

[MikeMike]

well, im looking to build the LCD projector, and would rather make the ballast than purchase it if it is cheaper. I am actually looking to use a 400w MH bulb so i was wondering if there is a way i can make a home made ballast, they dont look hard, but i do not know how to figure out exactly what i need...

is it possible?

Thanks

 

[pm]

Making your own ballast would be tedious - and at the end of the day by the time you buy the wire, the transformer, the large capacitor, I'm not sure that you'd do THAT much cheaper than the first hit for this on Google which is:
http://www.prolighting.com/sousm400q-k.html

which is a 400W ballast for $60.

There's this:
http://diyprojectorkits.com/pr...ctronic-coil-core.html

To make your own transformer, it's easiest to take apart a transformer and rewind it - you'll get best results this way. So go to Home Depot and get a mecury vapor transformer and take it apart and re-wind it.

http://web.telia.com/~u8592017...r/diy_transformers.htm

I wind my own electric motors for some projects and I can tell you it's super-tedious. I wouldn't recommend it. If you do decide to wind your own ballast transformer, then I highly recommend a pad and paper to keep count of the windings (since you aren't likely to finish in one sitting). The coil count is important and it's easy to get distracted and lose track - trust me on this. There's nothing like spending an hour winding a coil, and then have to unwind it because you lost track - or, much worse in my experience, is forget the current count finish it and have it be offset from what you need/calculated.

 

[MikeMike]

ah damn... i was hoping it was easier than having to wind a transformer... grr.

 

[Rubycon]

Problem with HID lighting is the response of the light output is very quick to input changes. Thus the 60Hz (or 50Hz depending on where you live) is superimposed very efficiently into the output of the lamp. (meaning it flickers) This can cause problems with a display. The best way to drive a MH lamp for projection is to use a switching mode driver with a much higher frequency (several tens to hundreds of kilohertz is common). This way you have a stable CW output.

 

[CycloWizard]

Originally posted by: pm
I wind my own electric motors for some projects and I can tell you it's super-tedious. I wouldn't recommend it.

You can buy coil winders that do the counting and such for you. I'm using one at work to make some motors right now. I should think you would be able to find a used one for pretty cheap and they don't really break down - the one I'm using is probably 40+ years old.

 

[Mark R]

Originally posted by: Rubycon
The best way to drive a MH lamp for projection is to use a switching mode driver with a much higher frequency (several tens to hundreds of kilohertz is common). This way you have a stable CW output.

MH have a problem in that you can get acoustic resonances in the arc, if the driver produces frequencies or harmonics at that approach the resonant frequencies of the dense arc. The resonances have been said to be in the 1-10 kHz range. This isn't the case with CFLs or linear fluorescents, which are quite happy running off a 10-200 kHz waveform (indeed, they operate much better on such a waveform). This means that MH ballasts need something significantly different to a conventional HF driver.

Instead, the driver must use a low frequency - typically 100-150 Hz. In order to avoid flicker which may be a problem with projection, filming, or high speed photography, the drivers are usually designed to produce as clean an AC square wave output as possible.

The design of MH electronic ballasts typically consists of several blocks:
1. Constant power DC-DC converter produces the DC voltage required by the lamp, and controls the power
2. Low frequency square wave inverter
3. High voltage ignitor

 

[Rubycon]

Originally posted by: Mark R

MH have a problem in that you can get acoustic resonances in the arc, if the driver produces frequencies or harmonics at that approach the resonant frequencies of the dense arc. The resonances have been said to be in the 1-10 kHz range. This isn't the case with CFLs or linear fluorescents, which are quite happy running off a 10-200 kHz waveform (indeed, they operate much better on such a waveform). This means that MH ballasts need something significantly different to a conventional HF driver.

Instead, the driver must use a low frequency - typically 100-150 Hz. In order to avoid flicker which may be a problem with projection, filming, or high speed photography, the drivers are usually designed to produce as clean an AC square wave output as possible.

The design of MH electronic ballasts typically consists of several blocks:
1. Constant power DC-DC converter produces the DC voltage required by the lamp, and controls the power
2. Low frequency square wave inverter
3. High voltage ignitor

Any references on the highlighted area? I've seen oscillations like you described. We have projector equipment using MH driven at 400kHz. It's essentially DC - arcs like DC and shocks like DC! (don't ask!)

 

[MikeMike]

i knew i posted this in the right forum.

 

[Mark R]

Originally posted by: Rubycon
Any references on the highlighted area? I've seen oscillations like you described. We have projector equipment using MH driven at 400kHz. It's essentially DC - arcs like DC and shocks like DC! (don't ask!)

Best I can find is:
Text. Describes several different types of lamp, and the areas where resonance occurs.

So, if your drivers arc and shock like DC - are they DC? 400 kHz AC arcs are very distinctive and shouldn't shock much - just cook. MH aren't normally run of DC in order to avoid electrolytic effects and migration of components of lamp to one electrode or other - but I suppose it would be one way of avoiding flicker.

 

[Rubycon]

Nice read thanks!

The polarization of arc tubes is apparent if not switched off after a while. This is why they recommend turning them off after 10 hours. Perhaps the signal is modulated?

Oh they shock and cook for sure. No hum just a loud hiss. Pretty scary stuff!