View Full Version : Video projector
08-08-2008, 07:12 PM
Hello, this is a little off the topic of home improvement, however I have a LCD digital projector, the bulbs are $400!!!!! So after doing some research I found airfield bulbs for the landing runway. There perfect, 1200 ANSI lumen s and rated at 1,000 Hrs. for $12.00. Also they don't require air cooling, which the projector has, so they might even last a little longer.
Anyways my problem is that the projector normally runs a 24v 150 watt bulb, without it the projector will not turn on. So I have to figure out a way to "trick" the thing in to thinking its fully operational.
I have experience with a wide range of electronics, soldering etc. I do not have the knowledge to disable the electronics to enable the projector, so I think my only option is to add a very large resistor, or perhaps a bunch of smaller ones on a breadboard in series. The bulb is a two pronged halogen, I don't know if it has a ballast, or if that would be a problem.
What do you think? Any suggestions are welcomed.
08-08-2008, 07:14 PM
The new bulb runs on a separate power source and is a non issue.
08-08-2008, 07:38 PM
There's a reason the bulbs cost a lot - color temperature consistency and (possibly) a built-in reflector. Plus, it is likely filled with an inert gas to help maintain the color temperature for longer. A typical incandescent without the inert gas will start to deposit vaporized filament metal on the cooler bulb surfaces almost immediately. You don't notice this much in a table lamp, but it becomes apparant quickly on a video display. But, I guess you could change the bulb way before they burn out if it bothered you and still be ahead monetarily. If I did the math right and remembered the formulae correctly (and don't quote me! check it yourself), to use 150W at 24v means the original bulb looks like a 0.61 ohm load. Now, finding a resistor that won't burn up at that power might be tough. There's probably a series load resistor in the supply, and they're sensing the voltage drop across it for the logic to say the bulbs on. There's lots of ways it could be done. Some might be easy to fool without creating all of the heat by emulating a bulb in there. Because of the amount of heat, the size and shape of the bulb and the ability of the envelope to disipate it well without shattering is a concern, too, in a confined space.
12-27-2008, 03:17 AM
If you run a projector with a halogen lamp, the image will look like 60's B/W films! Xenon or Metal Halide lamp are the types that must be used in projectors. they emit almost full spectrum like sun light, so much so that even corals in fish tanks get fooled and grow!
BTW,tricking the projector is also not that eazy, many projectors have an optocouplors or similar sensors that are in series with the bulb circuit - kinda in a current loop - to measure it's age and other parameters requird for projection-correction etc...
If projector lamps were cheap, no one will buy big-screen TVs anyway, so there is a marketting element too is behind this pricing policy! LOL
12-27-2008, 09:49 AM
Anyways my problem is that the projector normally runs a 24v 150 watt bulb
You sure about this? The $400 price and the 1,000 hour runtime suggests the lamp is a short arc lamp which is typically used to light LCD projectors and they don't run at 24V. The parabolic reflector is as much of the lamp assembly as the bulb - you're not going to get much light through the optics unless you duplicate the reflector characteristics also.
There's many safety interlocks tied with the lamp driver circuitry. You're not likely going to bypass any of it successfully.
Please post the make and model # of your projector.
If I did the math right and remembered the formulae correctly (and don't quote me! check it yourself), to use 150W at 24v means the original bulb looks like a 0.61 ohm load
150W / 24V = 6.25A
24V / 6.25A = 3.84ohm load.
If it was a 0.61 ohm load the bulb would be pulling 944W.