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Old 6th July 2002, 04:27 AM   #1
diyAudio Member
 
Join Date: Jun 2002
Location: sunderland united kingdom
Default using alternative lighting in projectors

would it be possible to use another light source in a commercial lcd projector ? and if so would it be possible to use the projector without its original lamp by using an external bulb and ballast, by somehow making a bigger box outside the projector and directing the light into the projector, does anyone know if this is possible ?and does a commercial projector use a ballast seeing that it uses metal halide bulbs so that you can use another bulb and get the power from the projector or do projectors not have ballasts in them, does any one have any experience or ideas using an alternative light souce in these type of projectors ? as the lamp costs in these types are horrendous

any help appreciated

fido
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Old 7th July 2002, 12:56 AM   #2
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Join Date: Dec 2001
Fido13uk,
as far as i know, most projectors will only start if a lamp is plugged in. Using an external lamp would mean to circumvent completely the projectors power controller or emulate the presence of a lamp.
Doing that is only possible, if you can get the electronic schematics of the projector and this will cost you $$$.
If another lamp can produce the same light beam it could be possible by mirroring the light into the original light path.

xblocker
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Old 7th July 2002, 02:46 PM   #3
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thanx 4 the reply, could it be possible to somehow trick the projector into thinking there is a lamp in there by linking the circuit where the bulb would have been or even using the same power supply to link to another outside lamp ? or even take the bulb from its holder and replace with another bulb of the same wattage voltage and lumen rating.


fido
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Old 8th July 2002, 01:14 AM   #4
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my understanding is that it can be done......I am buying a projector with a dead bulb that the user put another duller bulb into.....i will see how he defeated the interlocks and then tell you.....it cant be to hard however, just takes time
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Old 8th July 2002, 01:29 AM   #5
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Thanx 4 the reply but it seems to defeat the object by putting a duller bulb in there doesn,t it ?

i suppose if you could find another bulb of the same rating it should work in theory, however i dont understand why the makers charge so much for a metal halide bulb when you can buy much more powerful halide bulbs for only a fraction of the cost of these projector replacement bulbs, i am suprised that there isn,t much covered on this topic in this forum, it would be interesting to get feedback from those who maybe have tried different bulbs and what results they got, I look forward to hearing from how you get on with the dead projector bulb as mine still has a few more hours to go and i dont want to investigate until it has died.
I suppose osram sylvania would sell bulbs of either the same or simalar rating just a case of searching for a supplier really, I was wondering though the metal halide bulbs that are for sale are usually much higher in lumen and wattage rating.

ps: do you know what kind and where he got the alternative bulb from ?
it seems that all hid bulbs need ballasts to run so projectors must have these built into them somewhere so another matal halide bulb should run from its power supply without adding another ballast

cheers

fido
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Old 8th July 2002, 03:19 AM   #6
woneill is offline woneill  United States
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Hi All,

One of the big differences between the "projector-style" MH bulbs and the "lighting-style" bulbs is the spark gap.

The projection bulbs generally have a much narrower gap which acts more like an ideal point source than the lighting bulbs. A small point source of light is generally easier to focus into a uniform beam profile suited to the LCD panel being used - the larger emitting area of the lighting style bulbs is harder to focus into a uniform beam.

Another difference is the size of the bulbs - lighting bulbs generally have a double envelope which (I think) screens out much of the UV light coming from the spark gap, as well as providing a degree of protection from the inner core exploding. Many projection bulbs ommit this and are MUCH smaller.

Most projectors don't just use a bulb, they use a "light module". This is generally an assembly that contains the bulb, a suitable reflector - tuned to the characteristics of both the projector and the bulb - and a high voltage connector. This is all mounted in a metal package, designed to be physically, thermally and electrically safe if the bulb explodes... (Red hot fragments of quartz-glass flying around a room at high speeds can cause LOTS of damage...)

Electrically, most projection bulbs require a pulse-start ballast containing an additional ignitor that supplies a high voltage pulse needed to ignite the lamp. Most of the 400W lighting style bulbs do not need an ignitor - the ballast supplies a high enough open circuit voltage to ignite the lamp.

Many of the projectors contain an electronic ballast and ignitor that is specifically designed to be compatible with the electrical parameters of a specific bulb - such parameters include:

1) Open circuit voltage (bulb not ignited - often 120V - 240V);
2) Cold strike ignition voltage (often @ 4-5kV for projector bulbs);
3) Hot strike ignition voltage (often @ 20kV for projector bulbs);
4) Operating voltage (bulb ignited - generally 50V to 120V);
5) Operating current (bulb ignited - often 2A to 7A dependent on power rating).

The electronic ballast built into a projector is in many ways like the 12V to Mains AC inverters available to power electrical equipment from a car battery. It produces a high power AC signal with current limiting. Some manufacturers build the igniter directly into the ballast. Othes employ a separate ignitor between the ballast and the bulb. Often the electronic ballast units operate at much higher AC frequencies than the magnetic types - reducing any flicker.

ALL electronic ballasts generate high voltages at high power and are VERY dangerous to play with!!! Only experiment if you are a trained Electrical Engineer, AND you are experienced in dealing with Switch-Mode Power Supplies and High Power, High Voltage equipment. They can easily kill.

That said, if you know what you are doing, it is often fairly easy to determine how the main projection electronics can tell if the bulb is working properly. Many electronic ballast units send a signal to the main electronics to indicate if the bulb is working. Working/Non-working is often indicated by an open/closed circuit from a relay. Very few devices use a specific voltage level from the ballast unit as these devices are prone to failure and could inject a high power signal into the sensitive electronics on the main board.

Some projectors have no connection between the ballast and the main electronics at all - and instead use a light detector built into the optical path to determine success/failure.

You might find that some OHP bulbs are a quite effective alternative light source (often requiring that he ballast be replaced by a simple diode-and-resistor combination as a power source) - IF you can handle the short ~50h life span...

All in all, be VERY careful...

Bill.
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Old 8th July 2002, 03:32 AM   #7
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i trust you know what you are talking about, so basically its probably unlikely that any of us are going to find a cheaper replacement bulb for commercial projectors as by your statement they sound like they are very specific bulbs and cannot be replaced by any regular metal halide bulb. one question i would like to ask is could the electronics inside my projecter i.e: lense lcd panels be used to make a diy projector that will last more than the regular 2000 hours if so i would rather salvage it for a project than pay the 400 for a measly lamp also are these diy projectors as good picture quality as the commercially sold type ? if so i would definately salvage my projector for to start a project, as the running cost of my projector is way out of my league really.

thanx for the reply

fido
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Old 8th July 2002, 09:48 AM   #8
woneill is offline woneill  United States
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Fido,

The general quality of the DIY projectors is actually quite good - not as good as the latest and greatest of the newest projectors, but equivalent to something produced in the mid 90's (say, a Proxima 2800 as seen regularly on Ebay).

Most people start with a 640x480 LCD Overhead Projector panel built in the mid 90's and going for less than $100 from Ebay or various other suppliers (check out the old DIY projector thread for suppliers). When used with a high brightness OHP, the results are not quite full DVD quality, but are much better than a normal TV (if watched with the lights off).

Many people have replced the normal short-life halogen OHP bulb with a 400W MH general lighting bulb which gives out MUCH more light, and will last for 20,000 hours +.

In this configuration, much of the light is lost by the normal OHP optics, and while the bulb is not an optimal point source, the larger case and loose tolerances of the design tend to make this less of a problem than if you were to try and use one of these bulbs in a commercial projector. Some people have gone the next step, and created a new cabinet and reflector arrangement - but are still essentially using the OHP configuration in a single enclosed box.

I tend to prefer using as much hardware from a dead projector as I can because I am not very good with power-tools, and the commercial units are generally much more compact than something built from scratch.

If you are at all competent with electronics, and are attempting to cannibalise an old projector, I would first suggest completely removing the ballast and ignitor and storing them away - you do not want them accidentally hitting you with a 20,000V belt while you are probing around. Then, see if, using a lamp or torch as a temporary light source, you can get the rest of the projector to fire-up - look for leads going from the ballast to the main circuit board.

Commercial projectors, especially if they use three panels for RGB, are generally much brighter than those that use one panel (the type used by the OHP Panels). This is why some projectors give very high lumen outputs with only a 200 Watt bulb.

If you can get the basic projector electronics working, then you can figure out a suitable light source for it afterwards... I have done this with a number of projectors for myself and friends.

I sometimes re-use the old ballast with a MH bulb of equivalent electrical characteristics (different mount/reflector), or cobble together something using the more standard 400 Watt parts, but sacrifice brightness for quality - only using a fraction of the total light...

If you have an old dead light module, you might want to check out what type the raw bulb was - you might be able to find its electrical equivalent at the Osram web site - they have basic data sheets for all their bulbs, and you might be able to re-use the ballast, and/or parts of the light module.

Be careful, though, if you intend to play with these things - the bulbs are VERY high pressure, and can explode in your face if stressed.

Definitely check out other opinions than mine though - there are some awesome people working on this stuff!!!

Bill.
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Old 8th July 2002, 02:06 PM   #9
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I consider myself qualified to go poking around on the insides. I've build HV power supplies for HeNe lasers years ago and still work with tube electronics so I think the ballast won't scare me.....i just need to find out the electrical characteristics of the bulb, or completely replace it with one from Osram......
By the way, Osram does make projector lamps that act as a point light source so that shouldnt be much of a problem after determining the appropriate electrical characteristics of the bulb



One last thing, if you are looking for a replacement bulb and yours currently works.....measure out the voltage at startup and when running.....so you dont get into the same situation that I'm in.
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Old 8th July 2002, 06:24 PM   #10
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thanx for that very interesting info lads, I do build my own programmers and dabble in electronics to an extent, but with these high voltages I suppose i would be a little wary of measuring the voltage at start up as i only use standard uk 240 volt multimeter and i,m sure this is insufficient for the high voltage it takes to start these bulbs, although i could take a reading while running normally, one thing about the bulbs that osram sell would they be that much cheaper to buy than buying a full lamp unit from a commercial supplier ?


thanx

fido
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