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 Post subject: I need a special kind of switch...
PostPosted: Fri Jun 06, 2008 5:01 pm 
Little Foot
Little Foot

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First off, I know this is not the right place to post this, but I have tried several sites and no one has given me any help.


Here is my dilemma:

I have modded my 360 so that the fans run off of an external power source. Now my fans run all the time unless I unplug them. Is there any kind of switch that I can use to take the fans' old power supply (on the mobo) and use it to turn on and off my fans. Here is the basic idea of the switch I am looking for (sorry for the crude image):

Image

I know they exist but I do not know what they are called...

It will take the power from the old power supply and use it to activate an electromagnet that will draw two contacts toward one another, which will complete the circuit to the fans and make the fans run when the 360 turns on. Any idea what it is and where I can find it?


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 Post subject:
PostPosted: Fri Jun 06, 2008 5:24 pm 
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its called a relay.

radio shack probably has em, they are pretty common. if they dont, digikey has every relay known to mankind.

takes 12v (typically) and uses that 12v to close the contact (which are typically rated 120v and a given amperage).

one way you can use them is you would use the 360 12v power circuit via the relay to control the 120v transformer (or whatever it is) that runs fans.

actually there are several ways to do it using the relay, they can have normally open, normally closed or both types of contacts.

they also come in other voltages for the pull in coil and contact ratings. depends on how you want to drive it and what you want to control.


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 Post subject:
PostPosted: Fri Jun 06, 2008 5:51 pm 
Little Foot
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THANK YOU!!!!


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 Post subject:
PostPosted: Tue Jun 10, 2008 12:21 am 
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I like the idea of a seperate fan PS, and have considered it myself. I know of the relay, but is there a time-delay type of relay. Like something that would run the fans for a couple of minutes after the system shuts down? ...or would that require some more complicated circuitry?


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 Post subject:
PostPosted: Tue Jun 10, 2008 3:33 am 
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not too complicated. a 555 timer IC (costs less than a buck) a couple resisters and capacitors. whole thing including the relay should be less than $5

how good are you with a soldering iron?


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 Post subject:
PostPosted: Tue Jun 10, 2008 11:23 pm 
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I took an electronics class in highschool. It's not completely foreign to me, but it has been a while.


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 Post subject:
PostPosted: Thu Jun 12, 2008 2:27 pm 
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bbies1973 wrote:
I like the idea of a seperate fan PS, and have considered it myself. I know of the relay, but is there a time-delay type of relay. Like something that would run the fans for a couple of minutes after the system shuts down? ...or would that require some more complicated circuitry?


Per Char Broiled you can use a 555 timer chip and screw with a few circuits. Personally I like and use the 555 in a number of applications but was never a big fan of it for what you want to do.

What you are looking at is commonly called a "Delay on Break" or "Delay Off" as well as a few other names. I like the 555 more in the delay on make or delay on than a delay off circuit.

Personally, quick & dirty as well as cheap I would use something like this:

Image

Any simple relay will work just fine. The circuit would work well using a 12 Volt coil relay. The power comes from a source other than the PC (obvious reasons). You can screw with the values of the capacitor and the resistor looking for a suitable delay. Increasing the capacitor will increase the on time after power is removed using the switch. We charge a capacitor and the relay is held closed. When we open the switch the relay is held closed through a charge on the cap. The cap will slowly discharge through the transistor. When the cap discharges to a point it can't keep the relay closed the relay opens.

Quick and Simple.

Ron


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