Hey everyone, I have a quick question....I was having trouble wiring my 120mm cooling fan, so I decided to temporarily use a small fan that I would normally use on my desk at work (like a cheap $10 fan or so from Walgreens) by putting it inside the box facing the bulb. It appears to be ok for a while, but after about an hour of watching a movie, the picture starts to get darker and darker and the inside of the box starts getting rather hot. I'm wondering if this would be the cause for the darkness, and if this would cause my box to overheat. What's the difference between using a big fan like that, as compared to a small 120mm fan? Does the smaller one have more voltage or cool the LCD much better? If so, I will definitely switch. I'm just wondering why this happens after about an hour or so of running my projector.

The key cooling principle is to keep the LCD from overheating by pulling cool, outside air constantly across the face of the LCD, around the fresnel lenses and UV shields, past the lamp and out behind the lamp via the back, bottom/top of the enclosure. You don't want to ever let enough heat build up across the surface of the LCD. Circulating the air inside with a desk fan mimics a convection oven and will cook your LCD. You need to pull the heat OUT of the enclosure. Don't worry so much about the lamp, it is engineered to run hot. Follow the tried and true guide.

Are you using an infra-red shield like a piece of tempered glass? This is like the glass in kitchen ovens. This will help immensely. You don't have to spend big $; the glass on a dead flatbed scanner is tempered and usually the right size.

Well, I have vents at the rear end of the box and everything, which I assumed would work the same if was to use a desk fan rather than standard computer-like fan. In that case, why would the desk fan be any different? I figured, if anything, that it would cool down the box more since it's bigger and closer to the lamp. Am I wrong? I do realize, however, that I dot not have much space above, below, or to the sides of the fresnels and LCD, as I thought it would be more efficient that way since it appears that it would keep less light from traveling through the box. What are you recommendations as far as spacing, how much light should I allow to pass through the fresnels, temperature of box, etc. in order to ensure it is getting proper air flow? Thanks for your help!

Like bevo77 said, the important thing to cool is the LCD. The fresnels shouldn't get too hot either (but if they melt it's not a huge financial loss like with the LCD). And also as bevo77 said, don't worry too much about the actual bulb, it can take the heat. Just make sure you don't have stagnent air around the bulb, make sure at least some air is passing over the bulb and out of the box.

The desk fan should work a lot better (it's probably just too loud and big to be practical) just make sure you've got it pointed at the LCD primarially (you'll probably end up cooling the fresnels at the same time) and the bulb secondarially.

I was confused about this originally as well, the bulb ends up heating the LCD because of the actual light heats stuff up (IR light especially). I'm not sure what the process is called (radient heating maybe?) but it's similar to our Sun heating the Earth, it's not like a furnace where it heats up air, which in turn heats our houses (which I think is probably called conduction).

Unlike what bevo77 said tempered glass wont help very much with what I'm calling the radient heat from the bulb. Tempered glass does not block very much IR, which I think is the kind of heat you want to block the most. I think all the tempered glass does is reduce the amount of what I'm calling conductive heating of the LCD.



Let me ask you: when the darkness comes, does the panel work as it should again after it's had a chance to cool down?

Bevo,

thanks for replying to my situation. I currently have a small desktop fan at the rear end of my box, which faces the bulb and the rear fresnel. That's the only option I have as far as which direction I can face it; primarily because if I put it on the other side to face my LCD, it's blocking the picture from my LCD and can not pass through the triplet. Is that right? I have it set up te right way, don't I? I have close to about a foot and a half of empty space between the back of the box and the rear fresnel; the bulb lays between the two. Is that too much room you think? I originally built my box too long, but figured I could still use it. Therefore, I have a lot space between my fresnel and the back end of the box. Meanwhile, there is no spacing whatsoever between the wood frames, which hold my lexan and fresnel, as I originally thought it would keep more light in so I set it up that way intentionally. Should I make room to allow the light to pass through? Would that be a factor? All help is appreciated at this point.

Definately don't blow hot air ONTO your LCD!

You'd probably be better off turning the fan off at that point... might be worth a try.

So, what exactly do computer fans do if they don't blow hot air? Do they retrieve the air, as well, which is something the desktop fans don't do? I obviously need some sort of fan in order to run my projector; well, at least if I don't want it to overheat, that is. In that case, what do you recommend? Is one 120mm fan enough, or would you recommend two? Also, where abouts on the box is the best place to install the fan?

Bevo,

to answer your question, yes, the LCD works fine again after it's cooled down. Just as soon as I notice it getting darker, that's when I shut it off. It works fine when I start it up again later, though.

Make sure not to conflate posts by 2 different people.

I'm just saying: Don't move hot air toward the LCD, you want to get the hot air away from the LCD.

(Thanks for the answer above too, I've been wondering that for a while.)

I understand not to bow hot air toward the LCD. By using small computer fans, does that retrieve the hot air that would normally be blown toward the LCD then? I'm just wondering the difference is between using a desktop fan and a computer fan that both have the same voltage. Thanks.

The fan should be mounted at the rear of your enclosure behind the lamp. Sounds like you have room for that. You may need two.

Your lexan and fresnels can be close together. Do your frames allow for a path for the air to come in from a slot between your fresnels and LCD around your LCD and back out? Is there a cool air opening/slot on the lamp side of your LCD? That air path is critical and there needs to be a good seal along that path so that the only air coming in is from the LCD opening.

Some pics would be helpful. Consult the guide.

Projectorfan,
Make sure your fan, whether or not you use a computer fan or desk fan (although I agree the computer fan is quieter), is working to suck cool air from outside in past the LCD, under your rr fresnel , past the light and out the back. Like the vent in your bathroom works, where the inside of your box is the inside of the bathroom. The vent sucks hot humid air out of the room and vents it to the outside. Like bevo77 said, pics would be great. The black screen thing happened to me on my ps1 pj and it is indeed because the lcd is getting too hot, once I re-thought my cooling system, problem solved.

I actually have no air flow at all between the LCD and frsnels, as I connected the LCD to the frame in which the rear fresnel and lexan are sandwiched. I actually duct taped the LCD to the wood frame so it would hang. I didn't know how else would work as far as hanging the LCD, so I taped it to the wood frame that borders the rear fresnel and lexan. Also, I did not leave any space above, below or to the sides of the frame the holds the rear fresnel, as I thought it was imperative to do it that way so no light would leak out. How much spacing should be allotted to the sides and top of the rear fresnel so air can pass through? I don't have a camera to take pics, otherwise I would. I'm sorry...

1/2 "

Would that be 1/2" for just the sides, or the top/bottom, as well?

just the bottom

Here, read through this, it'll shed some light on things. (you could take that literally or not I suppose)
http://www.lumenlab.com/forums/index.php?showforum=45

Well, I have the frame sitting flush at the bottom of the box and have roughly 1/2" or so of open air space above the fresnel. Would that be sufficient enough or does it have to be at the bottom? I guess my question is why would it matter if the space is at the top or if it's at the bottom? Thanks for your help!

As long as your vent hole is cut opposite that gap, which in your case would then be the bottom of your enclosure, which will work if you are planning to suspend or otherwise elevate your pj to get an outside air supply. The air flow has to run past the LCD, that is the cool outside air has to flow over the whole back side of the panel.

Th vent hole I have is more towards the bottom of the back panel. How much space should be in between the field fresnel and LCD, though? I currently have the frame of my LCD duct taped to the wood frame that holds the fied fresnel. This way it has something to support it since it has to be elevated in the box. Is that ok, or do I need to allow space between the fresnel and LCD; and if so, how much space in between one another?

15mm

I currently have it at 1 inch, as the wood is 1 inch and it's hanging right in front of it. I believe that should be ok, though, as the picture seems to be alright. I'm just wondering about the duct tape I have around the LCD that's holding it on. It's not currently allowing any air flow between the field fres and the LCD. Do you think I should remove at least some of the tape so it has some room for the air to get through?

Yes.

You need air to flow over the LCD.


Did you bother to read anything on this website before building your projector?

No, I just thought I would build one from scratch without any clue whatsoever. Geez! Projectors aren't something that result in perfection the first time around; and being that everyone sets theirs up differently, it's difficult to tell what specs are optional and what are required. Questions tend to come up once a projector is built and things aren't displaying properly, which is the problem I have come across. Mine just so happens to relate to cooling and air flow; otherwise, my projector is perfect. Thanks for the help.