Ballast Questions

[Guy Grotke]

I don't think there are any MH lamps that actually run directly off 120 VAC power mains.

The ballast is connected to the power main (be it 120, 240, 277, or 440 volts). It creates the voltage the lamp needs to run correctly. This is why you can use the very same MH lamp in the US (120 VAC) and most of the rest of the world (240 VAC): You just use a different ballast or a different input tap on a multi-voltage ballast.

[telemonster]

Right...

That is why I wasn't sure if the magnetic ballast from a warehouse type metal halide fixture would drive the smaller short arcs. I was just thinking it should be initial firing pulse, then power to keep the arc. But evidentially there is more to it than that.

I emailed warner power to get a quote on this:
http://www.warnerpower.com/pdf/HMIMSR1200_1.pdf

It looks physically small. How much can it possibly cost...

My biggest worry is the LCD will turn black.

With a cold mirror to dump the IR, and alot of air movement across the LCD... think it will still absorb too much heat?

[Guy Grotke]

The cold mirror specs I have read usually claim they pass over 90% of the IR. With a 1200 Watt lamp, I guess it gets pretty important just how much over 90% is passed! Even if it was just 90%, it would be like running your LCD with an unfiltered 120 Watt lamp. Plenty of DIY projectors have been built with 150 Watt lamps and minimal heat control.

I think if you control the hot air well, you won't need additional filtering to remove heat. Just make sure you get a lot of air flow over the lamp surface, and that all of that air gets dumped outside the projector.

If you build it, and then find that it does overheat the LCD, you could add a sheet of Rosco Thermasheid film just before your condensor fresnel. Or maybe a piece of diyProjectorCompany's IR filter glass. Neither one would change the optics distances.

And I bet that Warner electronic ballast is incredibly expensive!

[Squalish]

The heat doesn't just disappear when it hits the mirror, some gets absorbed by the mirror, the rest hits your box.

A 1200w heater in a box is going to require some cooling, regardless of if there are heat-sensitive things inside, just to prevent being a fire hazard.

And I recommend trying for a hot mirror instead of a cold mirror, much easier to fit the beam needed for a short FL fresnel.

[Guy Grotke]

Hot mirrors are easy to add as a retrofit, since you just stick one right across the light beam and the IR gets reflected back. But if you look at where exactly that IR goes, it ends up scattered all over the light engine compartment. That's just the consequence of the angles of incidence.

Or you can use a 45 degree hot mirror placement to direct the IR to one specific target, like an air-cooled heat sink. That would make it a lot easier to get that heat outside the box. But if you can fit a 45 degree hot mirror, then you could fit a 45 degree angle cold mirror instead. Then the IR passes through the mirror to that heat sink I mentioned, and the visible light gets reflected toward the fresnels. Picking one over the other may be decided by the desired projector size or the expense of available dichroic mirrors.

Any of these can redirect over 90% of the IR before it gets to the fresnels. Then it is just a matter of how hard it will be to keep the light engine area of the projector cool. And I agree with Squalish: 1200 Watts is enough to heat Your room in the winter!