Instead of few fans at 12v, anyone try many fans at 7v?

Hey guys, im not sure yet how everyones powering their projectors. I figure id use an old PSU out of a PC. Most fans i see on here are the cheapo PC fans. At full 12v they run fast, and LOUD. Well us computer modders who like a quiet PC will often connect the +12v to one side of the fan, and the +5V of the other, resulting in 7v. The result is a SILENT fan, that sitll moves air. however, then one requires MORE fans.

Im one who likes to keep everything quiet. So im just wondering whos experimented with what. Just throwing the idea out.
 

Me2!

Member
2004-12-27 10:11 pm
BC
7v. Great idea. :D

Has anyone found a quiet household fan ~6" @800 rpm? I was after a bathroom vent fan but the quiet models get expensive. I bought a $20 basic bathroom vent fan at 50cfm (home depot) and its fairly quiet because it's not too fast. You can wire it to your 120v rail. Maybe i'll try reducing it to 80v. That should be perfect. Thanks for the idea!
:D :D
 

pinkmouse

diyAudio Moderator Emeritus
2002-04-03 7:15 pm
Rotherham, England
After being reminded gently, here's the simple circuit you need.

C1 should be about 0.1uF, value not really critical, D1 should be 1n4001.

To calculate R2, just measure the resistance of your thermistor at room temperature, and R2 should be around half that.
 

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its an RPTV lens off of ebay. The seller says its f/1.0. Ill take some pics when it gets here. its not 35mm. Back diameter is 5.25, thats all i know ATM.

There is a mitsubishi lens on there with an f/0.95, from an RPTV. bout 20$. Got a small rear diameter though.

I beleive the seller, after talking to others on here, ive found RPTV and CRT lenses rule for this, however we are limited terribly because of the small LCDs. I plan on just using a PSone LCD for my first project. i saw some results on the thread how to strip them, it actually isnt bad. One guy took a 2.5meter screen shot, though its diim, you cant really see pixels at all.
 
pinkmouse said:
After being reminded gently, here's the simple circuit you need.

C1 should be about 0.1uF, value not really critical, D1 should be 1n4001.

To calculate R2, just measure the resistance of your thermistor at room temperature, and R2 should be around half that.

can you specify the nature and value of the thermistor ?

Thank you
Phill
 
pinkmouse said:
After being reminded gently, here's the simple circuit you need.

With the thermistor in that position, it needs to be a positive TC, not the NTC shown, or the fan will slow down as the thermistor warms up. And suitable PTC thermistors seem hard to find.

Using an NTC but swapping it over to R2 position, the 317 doesn't seem a good chip for the job - the L200 regulator with its higher multiplier in the output voltage formula

Vo = 2.77(1 + R/Rth)

gives a better response.

Oops! I meant replying in the thread linking to here. :eek: