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i need a switch that automatically turns on a 220 volt when computer get turn on

neverthought

Jul 9, 2010
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hi
i strand in a situation
a computer turns on automatically and i need to run an 220 volt fan when its turns on
fan can not run constantly
i want to know if anyone knows a circuit that switch fan on when computer turns on an switch off when computer shut down
merci
 

davenn

Moderator
Sep 5, 2009
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14,011
hi
i strand in a situation
a computer turns on automatically and i need to run an 220 volt fan when its turns on
fan can not run constantly
i want to know if anyone knows a circuit that switch fan on when computer turns on an switch off when computer shut down
merci

You could take a line off the +12V or +5V supply rail in the computer and use that to operate a relay that has 220V rated contacts that will turn on supply to the fan.
Thats the most simple option.

does it have to be a 220V fan ? what are you cooling ? is it a physically a large fan
or something small for additional cooling of the computer ?

Dave
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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I have seen several of these devices. I ended up purchasing a power board that does just this. It turns on and off a heap of AV gear when I turn my TV on and off. (I have one of these -- although not purchased there.)

We've had questions like this previously. The problem is that, although the circuit can be pretty simple, building one yourself is probably not warranted unless you *really* can't get one locally, or you're doing it for a learning experience.

As always, I would urge that learning experiences are best kept some distance from mains voltages.

If you really want to make one, the simplest option is to place diodes in series with the load to get an approx 3V drop across them (so 4 diodes pointing each way) and place a solid state relay across them. Use the SSR to control the other loads. Just beware that at 10A, 30W would be dissipated in those diodes (possibly more) so it's not a great solution where the load draws a heavy current. If the SSR cannot be driven from AC (or if in doing so it turns the load on and off each half cycle) then you'll need to rectify and filter the voltage you get across those diodes.

davenn's suggestion is a good one if the controlling device has a power rail that can be easily tapped in to.
 
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