DIY-Projector Plans and theory collection !!

[rcabezas]

On the subject of cooling the bulb. What is the best approach for when the projector is turned off? Is it OK to leave it to cool itself down? Or should I keep the fans running for a while. Any ideas?

Raf.

[bobharry]

I was just about to suggest the barrier between the lamp and condenser then I read that you'd already thought of it. Wouldn't an IR filter work better? Because it should be designed to take a lot of heat, then theres the other obvious advatages too.

[ace3000_1]

I was just about to suggest the barrier between the lamp and condenser then I read that you'd already thought of it. Wouldn't an IR filter work better? Because it should be designed to take a lot of heat, then theres the other obvious advatages too.

Yess and no, an ir filter might over heat the bulb thats where i thought in the temperd glass, ir filter also doesnt stop much heat compared to cold mirror that close to the bulb.

[ace3000_1]

On the subject of cooling the bulb. What is the best approach for when the projector is turned off? Is it OK to leave it to cool itself down? Or should I keep the fans running for a while. Any ideas?

Heya Raf, i let mine cool down without the fan, having a fan running on a hot bulb without the lamp being on is infact more dangerous then with the lamp on with the fan at the same time, having a fan run on after the bulb is off may cause it to crack as the glass may contract too quikly, condensers also are viable to the same problems.

One thing ill tell you guys not to do at all ever, never turn on a fan when a lamp and condenser is hot, the lamp will surley explode and you can kiss your condenser goodbye, this is caused from too much of a temperature variance to soon, turbulent cold airflow over a lamp can cause the same problems hence why sucking the hot air is safer. never run a fan on a halogen either as they will surley explode, if it dont, you run a very high risk, a finger print can wipe out a halogen, same with metal halide, but most metal halides are protected by the outer shell, halogen have no protection whats so ever.

Trev

[rcabezas]

Thanks for the reply, Trev.
I agree with what you said, it makes sense. It's just that I've noticed that commercial projectors keep the fans running for a while after the lamp turns off, and was wondering why.
Anyway, I will do just that, suck the hot air off of the bulbs case and not blow air directly to it.
I ordered fans that ramp-up as temp rises; are they OK for a PJ, or are they a bad idea?

Thanks!

Raf.

[loke33]

Hey guys,
I'm new to the forum and have been allocating about 5 hours every day to reading the posts on this site, there is alot of information out there.

Anyway, to my question. I looked at mathias' picture of mirror size calculations and I had a basic question. I from what I have gathered one must match the fresnel's (the one between the light source and LCD) focal length with the distance from the light source, or the condensor. With a mirror does one only need to measure this focal distance as the distance from the fresnel to the center of the mirror and then off at a 90 degree angle to the light source. Sorry if this is a newb question or it has been covered in another forum, I havent found it yet and I have done quite some extensive searching. Thanks in advance.

[rcabezas]

Well, after seeing smoke coming out of my fans when I turned them off with the light; I decided to leave them running for a while after the lamp is turned of.
I'm thinking about programming a small microcontroller to do all that for me.
(turn fans on, lamp on, lcd on, and also off at the right times when a switch is pressed)

[rcabezas]

loke33:
The distance is still there, the mirrors just "fold" it. BTW, the mirror needs to be at 45deg, not 90, so that the light gets reflected at 90deg.

So, if distance without mirror is X, then distance from light to mirror and mirror to object should add to X also.

[loke33]

thanks for the reply rcabezas. Your answer was exactly what I was trying to say lol. Sorry i wasnt clear. Thanks again for the help.

[SmC252]

Originally posted by ace3000_1


This depends on rpm, ive seen 80mm fans push out 80 cf/m and 120mm's push out 94cf/m, the cpu fan on my cpu pushes out 54cf/m and thats an 80mm, bear in mind the noise factor though, the higher rpm the noisier the fan will always be.

Size and flow do corelate but I agree that some smaller fans will outflow much larger ones; it's all in the speed and blade design.

About the noise, I disagree 100%. The noise can for sure increase (and decrease) with rpm but the angle and shape of the blades is what will truely determine how loud or quiet a fan is. The S-shaped blades are usually the quietest, and the loudest are the flat-looking ones where you see only the edge.

-Steve