# Need a link: Timer circuit/device to keep fans running after shutdown



## CyberDruid (Aug 25, 2009)

Hey guys I was wondering if any of you electronic savants could point me in the right direction: I want to build or buy a simple timer that will integrate into a cooling set up to keep the fans running for a minute or so after shut down.

Ideally I would like it to run the cooling fans a minute before startup and a minute after shutdown. 

I was thinking something like a couple of relays, the momentary switch (FP power) would close the relay to the fan power (seperate from the PSU) then a minute later a second relay would trip momentarily to start the PC. Then to the second pattern: the momentary would shutdown the PC directly (or trip that relay momentarily) start the timer and a minute later it would open the second relay to stop the cooling fans.

Any ideas or link? Seems like it would be a simple breadboard circuit.


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## twilyth (Aug 25, 2009)

The standard micro controller timer is the 555 timer IC.  You vary the output time (in monostable mode) by changing the capacitor.  

I've never actually tried it myself though.  It seems a little odd to set the timing by resistor and capacitor, but you said you wanted simple. 

if you know any programming languages like c (no fuckin' + # &^*), basic, etc.  there are full fledged microcontrollers that you can get for like $5-10 bucks.  Check out the Nuts and Volts site for ideas


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## pbmaster (Aug 25, 2009)

Interesting idea you have. I think Enermax did the same thing with their Ininiti line of PSU's, except it just kept the fans running after shutdown. Theory was to completely vent all the hot air rather than have it build up in the case.


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## KH0UJ (Aug 25, 2009)

CyberDruid said:


> Hey guys I was wondering if any of you electronic savants could point me in the right direction: I want to build or buy a simple timer that will integrate into a cooling set up to keep the fans running for a minute or so after shut down.
> 
> Ideally I would like it to run the cooling fans a minute before startup and a minute after shutdown.
> 
> ...



are you using an independent PSU just for the fans sir if so, then you can use the time delay module for the A/C contactor, 2 pc. 12V mini relays, turn on the PSU for fans then after a minute (depending on what you set 3 seconds- 5 minutes) it turns on the main rig, 

if you`re interested im gonna draw the whole simple circuit after work

but first im gonna need the total fan`s amperage so that you`re gonna use a small transformer with bridge diodes and a capacitor so that its compact.
here`s a link if you wanna build the timer circuit: http://www.aaroncake.net/circuits/relaytim2.asp

ived used these technique on all my assembled repeater modules before to control the delay lines on the transmit


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## CyberDruid (Aug 25, 2009)

SWeet!


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## KH0UJ (Aug 25, 2009)

Here it is sir its still partial, I keep it simple with only transistor and a capacitor that makes a delay in the OFF scenario(3 seconds to 2 minutes), im still figuring out how to delay the ON scenario

how many seconds do you want on the ON scenario sir? 

First turn ON the switch to turn ON the fans relay then XXX seconds then partial relay ON for 1 second to turn ON the rig`s switch

The OFF scenario is simplier, cause if you shutdown the rig, the main PSU +12v side will cut off the K2 relay, then the C2 capacitor will slowly drain out of voltage until it cannot trigger  the base of the Q1 thus cutting OFF the K1 then turn Off the fan

The D1 & D2 serves as coil induction arrester, cause coil loads can induce spike voltages in turning OFF, so I just put it together with the circuit to prevent relay induction.

Edit: I forgot to label the capacitors with the (+) polarity and the base, collector, emitter labels, I uploaded another picture


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## twilyth (Aug 25, 2009)

What would be the easiest way to implement this?  Breadboard?  PCB with soldered wire connections?

I'm always getting excited about some new project but then I think about having to etch a PCB.


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## KH0UJ (Aug 25, 2009)

twilyth said:


> What would be the easiest way to implement this?  Breadboard?  PCB with soldered wire connections?
> 
> I'm always getting excited about some new project but then I think about having to etch a PCB.



I think breadboard is neat cause you can position uniformely the parts, (like aftermarket look) but I like also the soldered wire connections I tested it earlier with only soldered wires (messy but it works)


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