computer fan cooldown after shutdown

[PolskiSpirytus]

I was brainstorming an idea for two exhaust fans to stay on after the computer shuts down for about 5 min (give or take some) using capacitors and a relay to cut of the power to other components when the power is shut off except for the two fans... only problem is finding a capacitor(s) that would equal out to 12v and drive the fans for a few minutes after the power has been shut down (the fans that would be powered by that are 12v 0.5A 6W (two of them would be 1A and 12v) so I'm looking for some assistance on what uF capacitor(s) I should get to let that work for around 5 min...

Any help would be greatly appreciated...

 

[Boncuk]

Hi,

using caps to have two fans of 1A total running for 10 minutes would require a cap value of 600F. There are supercaps out there with a capacitance of 1,200F, but their charging voltage is limited to 2.5V.

That means you can get to approx. 12V by connecting 5 caps in series (12.5V), thereby reducing the total capacitance to 240F (1,200/5), resulting in a fan operating time of four minutes.

I suggest to use an external power supply and have the funs operating for any desired time period.

Boncuk

 

[blueroomelectronics]

Why do you think post cooling will help? Your PC is not a car engine.

 

[first_mcs]

You should be use external power supply such as 12Vdc.
this web is 5 minutes timer delay relay circuit
Or the easy way to finish fast project ,you should be buy analog timer at amazon .

Omron Delay Ac240/dc100-125 Omron Analog Timer

 

[crutschow]

I'm with Bill. There's no reason to operate the fans after the computer shuts down. Since the source of heat is removed when the power stops, then anything inside will not get any warmer than it was when it was on and the fans were running.

 

[Torben]

I'm with Bill. There's no reason to operate the fans after the computer shuts down. Since the source of heat is removed when the power stops, then anything inside will not get any warmer than it was when it was on and the fans were running.

I'll third that. Unless there is some hidden reason to want to do this--say, you want to hide the fact that the computer was on and therefore want to shorten the time it takes components to cool down--it would seem to be pointless.


Torben

 

[PolskiSpirytus]

First of I'd like to thank you all for replying...
now as in for the reason why i want it to run a few minutes after shut down; I've just build a new computer with the i7 processor and that thing builds up enormous amounts of heat... and I just want it out of there by creating an exhaust that would take it outside the room, since when the computer is on the room heats up very quickly, so the reason for having the fans be on after shut down is so that the heat that is in the computer after shut down gets out of there and does not sit around and act like an oven after cooking and heating up the room more.... (now as for just some info on how much heat comes of that computer It might not be that much after shut down but i like to eliminate the heat...) but for now this is an idea that i had in my head, which means one of two things I might forget it or do it at one point...

again thank you all for your input...

 

[blueroomelectronics]

The i7 doesn't need active cooling down else the motherboards would do it automatically.