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ATX PSU switched Aux. AC out?

Posted on 2001-07-22
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Last Modified: 2009-07-29
AT PSU's often had a useful auxiliary AC power-out switched via the main case switch. This meant you could power on and off printer, monitor, audio, MIDI devices, Palm cradle etc. all with a single switch.

With ATX PSU's the AC power-in is transformed and rectified and feeds the 5VSB output, so the PSU can be "woken-up" by case switch, LAN, Modem, Mouse double-click, or software. This usually means that any auxiliary AC power-out is hard-wired to the AC power-in. Thus if the power in is left on for "wake-up" purposes, any peripheral device connected to the aux AC out is also on and needs to be switched on/off separately.  In which case, you may as well use a separate AC feed as use the aux AC on the ATX.

Does anyone make an ATX PSU where the aux AC out is switched "usefully" by the wake-up? Failing this, what is the easiest way to modify the PSU so this happens?
e.g. 12V coil relay across wake-up operated -12V to Ground with mains AC across relay outputs?  Has any one done this successfully? Is there enough power on the 12V stage to handle a relay which will be "on" whenever the ATX PSU is in woken-up state?
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Question by:obuckley
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by:genguy
ID: 6306775
I haven't seen a atx psu that has an aux output, let alone a swiched one. I think your best bet is to build your own. A two pole Releco ice cube relay takes only milliamps for the pull in coil, the 12v from the psu is plenty. The contacts are rated for 10 amps, so you can run a fair sized load. Use a model with diode protection on the coil so you don't get spikes from cemf. Make sure you fuse the output of the relay so no one plugs a space heater or something into it.
Relay p/n C7-A20DX12VDC
Base p/n S7-M
Any similar relay with a diode will work fine.
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by:genguy
ID: 6306792
Another option is an X-10 setup, these are really neat.
http://www.smarthome.com/1140.html
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by:pbessman
ID: 6307504
I have an ATX PSU with the aux out and have considered hooking my monitor up to it. I even bought the necessary cable to go from the back of my PC to my monitor.  I am shy about that as so many people in my area have failing power supplies because the electric companies lines are so bad even with surge suppressors the Power supplies seem to fail quite frequently.  Yes, I am looking at a UPS but I have heard that that just adds to your monetary losses, that they too would be stressed by the electrical system here.  Too bad power companies don't upgrade their cabling as often as the cable TV companies have been doing over the last few years.
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by:pbessman
ID: 6307507
By the way, my case has an AMD approved 300 watt power supply.  It was purchased in a Translucent purple case.  I am questioning whether or not it is really ATX as there is no power switch on the back, but it does support some of the other features such as software off and various "wake-on" services.  It was purchased from www.directron.com .
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by:obuckley
ID: 6310205
Genguy, Thanks. My PSU does have an aux AC out and about half the ones in my office do also - the HPs and the Compaqs don't, the clones tend to - but the few I've tested are all hard-wired. I'll try to get a Releco relay, but I have not met this brand over here (UK) I'll try the Web.

The X10 sounds interesting, but it is obviously geared to US 110v/60Hz mains and may not adapt well to 240v/50Hz operation even if I can buy the right plugs.

Pbessman, you have an ATX if it will do what you say. An easy way to tell is to look at the PSU connector to the Motherboard. ATs usually come with two in line six pin connectors, ATXs with a single 20 pin connector in two rows of ten.  If the problem is with your power co, it doesn't matter much whether you connect via the aux.out of your PSU or a separate mains socket as the power from the power co will screw you up equally either way. By the way, I got my Motherboard, CPU and RAM from Directron (TX). They really performed for me when I needed them to and I can highly recommend them to anyone.
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genguy earned 100 total points
ID: 6310808
Thats interesting, I have not seen an aux output on one since the old AT power supplies.
I checked that site, but could not confirm if they are AT or ATX.
They are probably atx, but of a design not available here in Canada.
As far as the relay goes, I just use this brand because of the quality, you can use any brand with similar specs. that is rated for 230? volts. They call the diode an "optional built in suppressor" guess it sounds better than "diode" in the brochure.
The part number above is for an 8 pin model.
I found a link to a supplier in the UK:
http://www.lpc-uk.com/releco/main.htm
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by:obuckley
ID: 6314796
Curiously enough, I located the same supplier yesterday, they mailed me back with price and availability today and I expect it delivered tomorrow or Thursday. Points awarded. Thanks for your help.
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by:genguy
ID: 6315517
Glad to help, good luck with the project.
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by:obuckley
ID: 6338148
Just to confirm, Wires from input AC socket go to physical mains on/off switch, from there to aux AC out socket and concatenated from there to circuit board of PSU. Unsolder both sets of wires from aux AC out, solder PSU circuit board connector directly to mains on/off switch. Re-use concatenating links from mains on/off switch to connect to commutator of relay. Unscrew PSU circuit board and lift just sufficiently to solder underneath. (I was lucky, my PSU board had spare unpopulated +12VDC and Ground holes in the PCB). Solder new wires between +12VDC to pin 7 of relay and Ground to pin 8 (7 and 8 are coil of relay). Solder new links between "normally off" side of relay and aux AC out socket (via 5A fuse). Total time spent 1hr 15 minutes, including opening PC, extracting PSU, fixing relay, re-inserting PSU, closing PC. Works like a charm. Now a single mouse click (middle button configured as double-click) switches on PC, Monitor, Amp, Synth, Midi keyboard, Printer and Palm cradle. Win 98 shutdown switches them all off again. Quite easy really.
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