Metal Halide overdrive

[mkl2]

It’s a common practice with filament based bulbs, mainly in flashlights. The concept it’s simple, sacrifice the bulbs life for some extra lumen output.
I’ve searched for overdriving metal halide bulbs but I’ve come out short. Not much really, just some references to overdriving fluorescent lamps using a “higher ballast factor (BF)” – (what a hack is that?)
Why do I want do to this? There are a couple of reasons:
1 – all diy projectors lack sufficient lumen output but have 10k plus bulbs. I do feel like by the time I’ll have to replace my bulb there will be laser based projectors commercially available .
2 – the 250W bulbs are generally smaller and have a shorter arc length. Maybe overdriving such a bulb I could reach 30k lumens output and have all the benefits of a 400W one in a smaller package. And when it comes to light engines small always means better.

So is this doable?

[pinkmouse]

Overdriving a discharge lamp will do three things:

1) Vastly increase the amount of UV emitted by the lamp.

2) Give a much greater risk of explosive failure, and when I say explosive, I mean it. I have seen lamps that have burst and taken out an entire optical train.

3) Dramatically reduce lamp life. A few years ago I was talking to a Sylvania rep, and he told me that a 20% increase in voltage over spec. will decrease the lamp life to about 10% of normal.

[mkl2]

1) That’s to be expected. But single end lamps have UV filters build into the outer bulb. And I’m not entirely convinced about this UV threat. I’ve yet to see an lcd damaged by them. More concerning is the temperature increase witch leads to number...
...2) Generally MH are exploding, but this feature depends on the type of bulb or how it is used. 24/7 lamps should be replaced at 75% of their life, but the ones with an on/off cycle tends to die quietly. Also, uhp lamps should be run only in enclosed fixtures, but the common MH ones can be run in any kind of fixture because the envelope will contain the explosion. Worst case scenario - the envelope bursts also – the lcd is protected by a fresnel, a low-e/ IR filter and in some cases a sheet of Lexan. The most common reflector in diy community is the Ikea napkin ... thingy. I am using a glass reflector, so I should be concerned a little.
3) 1000 hours... fine by me. Of course, only if there is a significant increase in light output.

So how do I overdrive a metal-halide; should I use a 500W ballast instead of the standard 400W one? And, of course, how do I get 500W; with two 250? This dual ballast thing I’ve seen it before with a mercury-vapor lamp, but I don’t know if they were in series or in parallel.

[cbm5]

You'll also significantly screw with your color spectrum by doing this.

[Guy Grotke]

If I were feeling so reckless, I would just use the wrong input tap on a multi-tap ballast. For example, run 240 VAC into a 220 or 208 VAC tap. But I would start with a very gentle hand, like a 5% voltage boost, which would probably increase the power by 1.05 squared = around 10%. Maybe a few experiments with an Variac autotransformer?

Another danger unmentioned: You risk burning out the capacitor if you get the voltage much higher, since they are not rated all that much higher than they need to be for normal operation.

[Miedosoracing]

Tell us what you have as far as ballast and light goes first. Because, if you have a 500w ballast, I would say a better plan would be find a 575w double ended and be done. It will put more light than the 400w. Also the arc is smaller. LL has a post. A guy has been testing overdriving the mh bulbs. If you go too far, the inside actually melts the glass fillament. Another number to look at, if you want the best brightness possible, would be use a 875w 71mm arc light and a 1000w pulse start ballast. It puts out 95,000 lumens so over pushing it will put you over 100,000 lumens.

[mkl2]

This is my ballast, it’s a 400W mercury-vapor (HPI). It doesn’t have a multi voltage input, just the 240 one. Also over-volting will stress the electric gear so that’s why I avoided using this term and call it over-driving instead. And it seams that I was right, it’s just ballast related. On another forum someone suggested that I use a SON ballast. These have more power, at around 4.5A vs. 3.3A for the HPI ones. I have a Philips 400W HPI-T Plus lamp, but there is only one mention in the data-sheet:

Can be run on HPI-gear as well as on SON-gear ("PLUS" concept). The results in both light output and color temperature are different.

Well, I found the specs for an Osram lamp and its clear, SON has more power at a lower color temp than HPI.
But now I want more, maybe two 250w sodium ballasts for a total of 6A (a 30% increase over specs).

I don’ want to use the 575W bulb because it will be hard to find and rather expensive.
Common 1000W bulbs are also no go because of that 70-ish mm arc length. If for some reason I’ll be forced to go ballistic I’ll use one of these: Osram Powerstar hqi-ts 1000 or Philips Master mhn-la 1000 (or similar laps from other manufacturers). Both have 95.000 lumens, 6000 h lamp life, 35 mm arc gap and more than 5500K temp. Only one drawback – at around 300$ a pop these are expensive stuff.

So the question now is how two ballasts can be wired to power up one bulb. This is the wiring diagram for the HPI ballast: