Hot, Hot, Hot!

[eelai]

just a quick question. how close is too close for a bulb and ballast? i'm trying to build the smallest enclosure possible with an m59 ballast and one of those huge mh bulbs and i've got maybe 2 inches of clearance between them. is this a bad/dangerous idea?

[snortonnorton]

i was wondering that too. but it's all relative.

so many variables. i'm using a large fan and thus gonna try putting the ballast in the enclosure. (cause i'm worried about trying to ground it if i had it outside of the mdf enclosure)

this guy is about 9 inches long, at wallyworld, the lasko fan brands. squirrel cage design so i can use pvc that extends to the outside of enclosure, then blow cool air onto fresnels/lcds, then just put a small computer fan that sucks out the old air at top of enclosure.

(second picture is it after i took off the cover, and my light was too bright from camera. sorry)

[snortonnorton]

apart

[Guy Grotke]

If you are depending on distance alone to keep the lamp from overheating the ballast, then that distance should probably be at least a foot. But that is not necessary: You should have some sheet aluminum between your lamp and ballast, so light does not go directly to the ballast (or any other parts but the fresnel).

The aluminum will act as a IR radiation shield. You can paint it flat black on the lit side, to make it more efficient at transferring heat. Cooling air should move around the aluminum to keep its temperature down.

With a good shield and air flow design, the ballast could be just a couple of inches from the lamp.

[snortonnorton]

cool, thanks for the tips guy, i'm still designing my enclosure while waiting to work out my lcd panel problems.

[eelai]

this makes me feel alot better about giving it a go. i actually got a little more space between the two by putting the bulb on the diagonal. the box will be a little wider but shorter also. i'm hardwiring a dvd player into the whole thing and the box became taller than wide. adjusting the bulb fixed both problems, i think. thanks for all the input. it's much appreciated.

[milihpen]

On a related note, how close can the bulb be to the back of the projector? I've got about 1.5" right now. If I install flashing, is that ok, or will it still burn the mdf? Should I paint the flashing black?

Also, what exactly is the point of flashing? Is it just to keep the enclosure material from getting too hot, or is it there to add light to the image?

[Guy Grotke]

If you put the lamp 1.5" from the mdf, it will heat it enough to burn it. If you put metal flush against the mdf, the lamp will heat it so much that the metal burns the mdf. (Exactly the experience of another builder on DiyBuilderGroup: He wondered what that funny smell was, until he removed the flashing and found the mdf charred!)

The ONLY way you are going to get away with 1.5" from lamp to mdf, is to mount a metal heat shield (ie. flashing is fine) about 1/2" from the mdf. Then run lots of cool air between the metal and mdf.

The purpose of a metal box around the lamp is to keep waste light from heating up the box. You need a precise reflector to send light rays where they will do some good. Light rays traveling in the wrong direction can only heat up your projector or wash-out your image.