Click to view attachmentOk here is my problem, I have built an original planned PJ and I am having a heat issue. I will list some data to maybe try to show what i have done wrong.

Enclosure is 16.75"W, 28.50"D, 12.25"H
17" HP L1755 LCD
Standard Fresnels for 17" monitor
400W SD400 bulb with reflector
(2) 120mm ac fans (100cfm each)
X10 heat barrier Lexan
There is foam seal around top, LCD, rear frensel.
Filter are nylons cut to size

In abiant tempatures of ~70 degrees it works fine, but once tempatures reash 75 degrees, the black blob shows its face.

I have tried rear frensel togetget and then 3/4" apart, I have even placed small fanns over the cooling slot (not sure if they are pushing enough air) the fans seem to slow it down, but still the black blob appears. I currently have the air flowinf down the back of the LCD and up the back of the rear frensel

I am curious is the 1000:1 contrast ratio is a problem.

I have enclosed some pics, how this helps. Any ideas or suggestions would be awesome.
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Make sure the slot between your LCD panel and the rear fresnel is as big as possible--the full width and length of the space between the two. Also, add a piece of tempered glass between the lexan and the bulb. (a junk flatbed scanner is a good source) This cuts down on IR really well. Do not push air into the slot with fans. Cooling is better by pulling the air from the back. Sounds like you've got the air path well sealed; the only intake should be from the slot.

If the slot opening and tempered glass do not work, add more air cooling capacity by adding more or larger fans in the back of the PJ. Good luck.

I will try the tempered glass and see what comes of it, i already have 2 100cfm fans, and not much room for more. But I'll do what it takes.

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You might try a lightbox to help issolate the heat and route it away from the LCD. Also, I had to remove my ballast from inside the box (although Im using eBallast) before the heat got under control.

Can you show us what it looks like with the cover on top ? How large is the slot on the top of the box ? How big of a gap is there at the bottom of your lexan and collimating fresnel?

gs

Click to view attachmentThe slot on top measure one inch, and the gap at the bottom of the lexan and fresnal is 5/8"

Heats a real pain.. ive built 2 projectors and both have or had heat issues.

First off, You should have plenty of cooling with your 2fans..

I suspect you are having troubles because you are letting the air pass down the back of the LCD then back up the Fresnels.

Really you should have the air pass down the back of the LCD then under the rear fresnel and heat sheild.

Ive found that by letting the air pass up and down you restrict it alot and it also allows the air to heat up more because its in the light path longer.

See if you can get the air to only pass down the LCD then into your light area.

Tempered glass shouldnt make a difference in your cooling.. Your lexan is fine. Adding another peice of glass will only make your projector dimmer, Use either the lexan or tempered but not both.

it looks like you have the FFC pcb board at the top of your lcd panel,, ??

if this is where your air intake is,,, that will be killing your airflow..

or am i not seeing the pic right,,,
nah scratch that,, have the stupid hat on today,, heheh

you need to have a sealed airpath to cool the lcd, I think you need to have the air flow in from the top slot, down between the rear fresnel and lcd and under the lexan, into the light chamber and out thru the fans, two should be more than enough. I use a 1/2" intake, 1/2" between the fresnel and panel, 1/2" under my fresnel/lexan. I use (1) 120 mm fan and it stays 10 degrees above room temp. is the intake the only place the air is coming in to the pj? are there any leaks from the front? do you have the airpath sealed with weather stripping?
you should also have a shield over the ballast to keep it from getting cooked by the light.

here is what my first pj looks like from the top maybe it will help

Hi,
I created two (2) cooling circuits for my pj and it worked VERY well. This makes one circuit cool JUST THE LCD and keeps the hot air from the light area from creeping into the LCD area.

I also have pressure and vacuum fans. (two fans supply air to the LCD, two fans supply air to the light box, 1 fan "sucks" air from the LCD region, and 1 fan "sucks" air from the light box region).

I had heat problems, and since I did this, no problem.

You must also use the UV filter, as this keeps UV from hitting your LCD and turning to heat (this might just be your problem). I did not see if you used the UV filter or not.

My LCD stays at about 83F all the time with no issues at all.

Good luck.

Ok, I have weather stripping sealing the LCD and rear fresnal/Lexan to the top cover, and about 5/8" gap at the bottom of the floor. I dont think heat in the light department is much problem ~110 degrees, I am NOT using a UV shield, I was unaware of using one. Does the UV shield make the picture dimmer? I have recently put a space of 1.50" between the LCD and Rear Fresnal. The spot only shows in the dead center of the LCD.

Bluesrocker22: Do you have a picture or diagram that shows your design? I would be intrested in looking at that.

Now if the room temp is 70 degrees this works fine, but with slight increase 75 degrees, it has issues.

What type fans do you recommend? Maybe my fans aren't pulling enough air, they say that are rated to 100cfm, but I am begining to wonder now.

Has anyone tried sealing off the LCD at the top and bottom and pushing/pulling air from the top staright down over the LCD and out the bottom?

At this point, I am encuraged to find a small AC unit for it

Oh well thats the problem.. you are pulling air from under the LCD instead of the slot..

Seal the LCD completely all the way around, Air should only be able to come down through your slot between your LCD and rear Fresnel, and out the bottom of the rear fresnel and heatshield.

Your fans should be fine.

Also if you are using Lexan XL10 you do not need to use a UV filter as it has one built in.

Here is a quick diagram of the cooling flow I used.




MUST SEAL ALL TO FORCE THE AIR TO TRAVEL DOWN ACROSS LCD, OUT BOTTOM HOLES IN WOOD FRAME, THEN AROUND EDGES OF WOOD FRAME.

Hope this helps.

All,
not sure why the pic is so small. never had that problem before.

The LCD is totally sealed to the enclosure, no air is leaking past the LCD Seal.

Ok, I would like to thank everyone for your ideas and suggestions. I think I have found a small solution to my heating problem. I moved the lamp from 8 11/16" to 11" from the rear frensal. I did not see a differance in the brightness of the screen and so far I have been able to run the projector for 4.5 hours without a heat issue, even in 77 degree room temp.

Hi,
Don't you want your bulb to be EXACTLY at the focal distance of the rear fresnel?

I think this makes a big difference. Especially if using a reflector.

Well when the center of the arc is EXACTLY in the focal point of the frensal the projected image is always brighter in the center of the screen, which in turn starts to boil the LCD liquid. As I pulled back the lamp the picture brightness seem to even out, worse case would be the center of the screen would be dim, but there is always room for adjustment. I am willing to lose 2-5% of the brightness if the LCD stays cool and can operate hours on end without boiling the LCD. In no case I am saying this is a fix-all, it just happened to work for me. There is alot of factors in the heat issue, in my case I have found that the front AG filter is alot darker than other 15-17" monitors, so I know more heat is absorbed.

My projector is acually a converted 15" projector (had a small accident with the LCD and a screwdriver slippage) And with the 15" (lighter AG Filter) there was no issue with cooling, and that was with the LCD not sealed in the case very well, I added the 17", sealed it to the enclosure and BAM the black Blob appeared.

I have tried everything short of adding a A/C unit to this projector, so losing 2-5% in brightness is acceptable to me. I will post screen shots as soon as I can find my camera.