Film-Tech Forum ARCHIVE: Vent collector for the back of an NEC projector

This is topic Vent collector for the back of an NEC projector - photo request in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Mike Blakesley (Member # 26) on 08-24-2011, 12:15 PM:

A while back, somebody put up a picture of a galvanized "collector" he'd built to gather up the heat that comes out the back of an NEC projector, but I can't find it....EDIT: Never mind, I just found it. But I think it would be good to leave this thread here for others who might want to build such a device. I'll put the pic here.

Posted by William F Green (Member # 3192) on 08-24-2011, 12:20 PM:

It's on this thread below - go to the last post and it's one up from that.
http://www.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=16;t=000001;p=8#000111

Posted by Mark Gulbrandsen (Member # 72) on 09-02-2011, 10:34 AM:

This is a good idea but you have too much open vent for the collector. I suggest placing an adjustable damper in the rear section of the Y so you can adjust the airflow back there. You are splitting that between projector and lamphouse and the lamphouse may be suffering on exhaust a bit. The use of a anemometer is highly reccomended. They are available very inexpensively on Ebay.

Mark

Posted by Monte L Fullmer (Member # 2797) on 09-02-2011, 02:28 PM:

quote: Mark Gulbrandsen
and the lamphouse may be suffering on exhaust a bit

....prob why the install of a booster fan for the console.

Posted by Justin Hamaker (Member # 2165) on 09-02-2011, 03:27 PM:

The whole purpose was to maximize air flow and bulb life. As I stated in the original post, this sends virtually all the heat up the vent and helps keep the booth very cool.

The thing we still need to figure out is an indicator light to show when our roof exhaust is not on or not working. We're thinking some kind of vein switch, but it needs to require enough air flow that it won't switch just from the booster fan. We had a belt break on the roof fan and didn't know there was a problem until the projector gave an overheat warning.

Posted by Mark Gulbrandsen (Member # 72) on 09-02-2011, 03:45 PM:

I think you missed my point though. It is possible to be sucking too much air up the back collector and not enough up the normal stack from the lamphouse. Your setup looks like it is doing just that to me and the only way you can verify air flow is with an anemometer (under $30.00 on Ebay). You have no way of controling how much air goes up that rear collector... and it's going to take considerably less air flow for the collector than the lamphouse stack will need. If you have a 600 cfm blower or are running 1600 watt lamps where that wouldn't matter [Cool]

but I doubt it. So if you are splitting your airflow evenly then your projector is only getting 300cfm... and what size lamp might you now be ruining?

Re: The vein switch... They can be good and evil at the same time although the intake on the NEC is totally filtered so you won't see the switch getting full of goop and dust like it does on all other brands. But I agree that some sort of indicator is nice. Even an illuminated switch just so you can see that it IS turned on. Normal service intervals play a bigger key to reliability... even if you have an airflow indicator switch are you still going to wait for the belt to break? Changing blower belts every 7 to 9 months even if they are not broken eliminates 98% of that problem, you will most likely still find them to be cracked if you bend them at a sharp enough radius. Once in a blu ray you'll loose a blower motor. Keep a spare on hand so you don't loose a whole day while Graingers sends you one via UPS. Belts are ~10 bucks. Refunds are far more expensive, a blown lamp and or worse broken reflector and heat filter is even worse. The reflector in your projector is ~7 grand by itself!

Mark

Posted by Monte L Fullmer (Member # 2797) on 09-02-2011, 04:59 PM:

Don't NEC units have a hi-temp safety where it will shut down totally if the unit gets too hot-first you get the hi-temp warning?

there is a little 4plex art house in this area and the owner called me up for an interesting service call: a 35mm console was getting pretty hot.

In this one house, they can do both 16mm and 35mm projection - and what the owner did was split the exhaust for the two machines..and I knew exactly what was going on:

The owner did the same: put a 6inch "Y" in the ceiling and didn't put a throttle plate in the stack attached to the 16mm (which wasn't used that much anyway), thus the airflow was split and hardly any exhaust was pulling the heat out of the console.

The owner couldn't understand that splitting airflow, the CFM's gets drastically reduced - why the 35mm console was getting hot to the touch.

Thus, had to explain that making 6inches as a whole number, then you times it by two making it 12inches, that times two becomes a division number for the CFM's heading up the stack for the 6inch stack size. Thus the fan was pulling 750CFM's before the conversion, now adding that "Y" divided that 750 to 325 and guess what: not enough CFM's to pull the heat out.

Owner then saw the light on that one and he did put in a throttle plate in that side of the "Y" to shut off the airflow.

Console cooled down after that.

-Monte

Posted by Justin Hamaker (Member # 2165) on 09-02-2011, 05:48 PM:

quote: Mark Gulbrandsen
Your setup looks like it is doing just that to me and the only way you can verify air flow is with an anemometer

You think this could be a problem even with a booster fan sucking air off the lamp house side and up the stack? The rear exhaust doesn't have any kind of booster on it.

Posted by Mark Gulbrandsen (Member # 72) on 09-02-2011, 06:37 PM:

The real problem here IS that you're dividing up your exhaust extraction 50\50 between the two. Without knowing your total extractor suction and the lamp size you are running I couldn't tell you so it's anybody's guess. If you can give me an idea of total CFM and lamp size I can give you a more accurate picture. Overall, this is a good idea that I will probably encourage folks with already hot booths to do but each situation should be fine tuned with a variable damper on the rear of the Y to be sure the lamphouse itself is not being short changed on extraction.
@ Monte... Yes, it'll shut off the lamp and give you a high temp warning. Ditto if the air filters become plugged.

Mark