Project: OHP MH Upgrade

or: I'm Too Cheap To Buy An LCD Projector

or: Heck, I'm Too Cheap To Buy A Decent OHP
  For those of you that want it, there's background data here.

  The idea for this project started with a member of the diyvideo.com forum who goes by the handle ywh.  He lives in China, and he modded a standard OHP to upgrade it from a 360W halogen to a 250W MH HQI.  Pictures here and here.  The credit for this idea goes to him.

  Prior to this, I was laboring under the assumption that (almost) all OHPs used an ENX/FXL type bulb.  It turns out I was quite wrong.  It is true that most of the OHP in the United States use this kind of bulb, but many in other countries (and some in the US) use an EHJ style bulb.

  The primary difference is that the ENX bulb has an integrated reflector, so it is essentially impossible to replace just the bulb part and re-use the  reflector (plus there is no MH bulb that small to replace it with).  The EHJ OHPs use a seperate reflector (and occasionally a condenser lens), so you can replace just the bulb.  The trick is retrofitting a (much larger) MH bulb in the space meant for a small halogen bulb.

  When shopping for an OHP, I accidentally won two auctions at once.  One was for an Apollo AI-10000 ($10), and the other was an Apollo AI-15000 ($20).  I literally paid as much in shipping as I did for the OHPs.  The 1000 uses an antiquated 600W halogen, and the 15000 uses a 250W EHJ bulb.  In spite of this, there was no discernable difference in their brightness at the screen. I suppose this has to do with the more advanced bulb, because the internals are almost identical.  As usual, my digital camera sucks, so pardon the poor quality pictures.

AI-1000 beside an AI-15000
  The 1000 is on the left.  It is made mostly of metal (whereas the 15000 is largely plastic).  That, combined with the fact that I supposed that the internals were designed to withstand heat from the 600W halogen bulb, made me decide to mod the 1000.  Neither one came equipped with an internal condenser lens.

  Good lord, look at the mess on that workbench...
Original Innards on the AI-1000
  This was the original unmolested innards of the AI-1000.  The bulb and reflector are in the center, the fan/shroud is at the bottom, and the resistor ballast (for dimming the lamp) is at the top.
bulb and ballast
  The 250W HQI bulb, the lamp holder, and the electronic ballast.  The bulb was $40, the lamp holder $10, and the ballast was a whopping $125.  Yikes.
OHP disassembled
  The lamp mount/reflector and fan assembly removed from the OHP.  The fan had to come out because the lamp holder would interfere wth it.
reflector
  This is a look at the reflector mount with the HQI lamp holder attached.  There is one machine screw on either side of the reflector that attaches the lamp holder to the assembly.  QED.

Reasssembly 1
  This is the ballast mounted to the outside of the OHP, with the wires routed through the casing.  Note the rubber grommets where the wires enter the metal casing:  this is an absolute must if you are to route wires through a hole in metal.
reversed fan
  This is the fan now mounted to the outside of the case.  I also reversed the wiring, so casing has positive pressure (blows air into the casing) just like the original.  Even with the shroud, about 1/4" of the fan spins unprotected.  Given that this is an older-style heavy-duty motor, I expect to end up with sliced fingertips at some point.
new innards
  This shows the finished installation interior.  The ballast wiring is spliced directly into the original wiring for the dimmer, so the fan runs all the time (when the OHP is on, of course) and you can turn the light on or off with what use to be the dimmer switch.  Not that you'd want to.  I dunno, it made sense when I was wiring it up.
DISCLAIMER:  Again, my camera really, really sucks.  These next pictures don't do the results justice.  Plus, I was sitting off to one side of the screen.  And it was 3am, so I was having a little trouble keeping the camera steady.
  Anyways, the projected image is just about filling an 80"-diagonal screen made from a stretched dropcloth.




TODO LIST:

There is a lot of light bleed, especially from around the fan port.  I tried to take a picture to show this, but my camera is not up to the task.  When I say a lot, I mean that with the fan spinning, there is essentially nothing blocking the bulb from shining into the room.  

(1) make a baffle that will both block the excess light and keep me from sticking my fingers into the spinning fan.

  The fan is an old-style heavy-duty one, and it's quite noisy.  The fan from the AI-15000 is whisper quiet compared to this one, and it's smaller to boot.  It might not move as much air as the heavy-duty model, but I appear to have absolutely no heat issues, so that's not a concern.

(2) swap fans to reduce the feeling you're watching the movie on an airplane.

  The HQI setup was quite pricey (about $180 all told).  I originally balked at using a tube-style MH bulb because I thought they would be too large.  However, the 250W HQI bulb is quite large (about 3/4" diameter), and it fits just fine.  Figuring out how to mount a single-ended medium-base bulb might be a little tricky, but seeing as the standard 250W cap-and-ballast setup is about $40, it put the cost of a 250W MH OHP retrofit down at about $100, which is much more reasonable.

(3) perhaps try to mod the AI-15000 with a cheaper single-ended MH bulb/ballast without losing lumens.

  As you can see, the image is almost TOO bright now, and it's overpowering the measly 100:1 contrast ratio of my Ovation 820 panel.  

(4) consider buying/destroying an XGA LCD monitor with good specifications.

  Man, these pictures suck.

(5) buy a decent digital camera.  And for god's sake learn how to use it.