• We’re currently investigating an issue related to the forum theme and styling that is impacting page layout and visual formatting. The problem has been identified, and we are actively working on a resolution. There is no impact to user data or functionality, this is strictly a front-end display issue. We’ll post an update once the fix has been deployed. Thanks for your patience while we get this sorted.

want a relay to control my accessories

Status
Not open for further replies.
B

bwanaaa

Senior member
when my pc shuts off, i want to shut off a bunch of other things too-speakers, light, monitor.

to do this i need a relay but am a little perplexed on the correct wiring.
(Please ignore the periods. they are necessary to make this drawing look right but have no meaning)

Voltage_____|
. . . . . . . . . .|
1___| . . . . . |
. . . .| . . . . . |
. . .coil = ). . |(
. . . .| . . A. . .B
2___| . . .|
. . . . . . . |
. . . . . . .R1 (lights, speakers)
. . . . . . . |
Neutral__|

When the coil is energized(current from 1 to 2), the switch moves from B to A.

Is it workable to also connect Voltage to 1, then to connect 2 to the hot leg of the pc power cord and then the neutral leg of the pc power cord to neutral? It would look like this:

Voltage_____|
| . . . . . . . . .|
1___| . . . . . |
. . . .| . . . . . |
. . .coil = ). . |(
. . . .| . . A. . .B
2___| . . .|
|. . . . . . .|
PC. . . . . R1 (lights, speakers)
| . . . . . . .|
Neutral___|

The idea is to get current to flow through the coil when the pc is on. This allows current to flow through R1. And when the pc is off, there is current through R1.

The resistance through the coil is 2 kOhms and this is an A/C relay rated at 10 amps for 120 volts. or is this stupid because insufficient current will flow to the pc because the coil resistance is so high?

 
I would do this as a DC powered project and not try to use the current of the AC going to the pc supply. The current of the AC powering the pc would burn out the coil of the relay. To do that right you would have to use much more complex circuitry. It is much easier to tap into the pc power supply wiring from a drive connector, +12V supply and use that.

The AC rating of 10A@120VAC is the rating of the contacts.

The coil of the relay will work fine with the pc but you do need to put a diode across the relay coil to drain the voltage that results when you switch off the relay.
http://www.kpsec.freeuk.com/co...ents/relay.htm#protect

I would also put a fuse between the pc power side and the relay.
Best would be to optically isolate it completely from the pc but that involves a lot more circuitry.

If I wanted to do it a quick way and not have a lot of parts I would use 2 diodes, a fuse , and a relay. The second diode adds some protection should the hot from AC cross to the + DC of the pc.

so it would be like this picture.
http://i41.tinypic.com/2yzg6t4.jpg


The diodes are .99 at RS
http://www.radioshack.com/prod....jsp?productId=2036270
 
OK so you want to use the coil as a current detector. Not gonna work. 2k ohm coil will drop the current so much that it won't run the PC. Even if you get a lower current coil this isn't the way to go.

The proper way to sense current via AC power cord is to use a shunt (0.1 ohm resistor that can handle 200+W) + diode + opamp that drives a transistor, that runs the coil.

However a better and cheaper and easier way might be to use +12V line from the other side of your PS, a 12V relay (or SSR). Since +12V is off when the machine is off the coil will release the relay and shut down your other equipment.



 
Unless you're really into at-home-modding, why not just connect everything to a power strip? Is that extra step of flipping a switch that much trouble?
 
Status
Not open for further replies.

TRENDING THREADS

Back
Top