ATX power supply, no mobo, momentary switch question

[quarterback]

Okay, we all know that ATX power supplies want to be hooked up to a mother board in order to turn on.  When you hit the momentary switch on your PC's case, it sends a signal to the mobo which, effectively, shorts a couple pins on the PS connector and it turns on.

If you're running an ATX power supply withOUT a mobo, you can manually short these two pins together and the PS will turn on.

However, I'm not sure if this will accomplish what I want and I'm hoping that somebody here can tell me how to do what I'm looking for.

I'm not using a motherboard.  I want to use a power supply that has a momentary switch so, when power is removed from the PS (IOW, the AC power goes out) and then is REapplied (IOW the AC power comes back on) the Power Supply does NOT power back up.

Unlike an ATX supply, in an AT power supply the switch actually controls the flow of power.   So if the switch is left "On" then cutting/reapplying AC power just turns the PS on and off without any more touching of the switch.  I do NOT want this.  I want the opposite of this.

If the ATX was hooked up to a mobo, this wouldn't be a problem.  But I believe that jumping the two pins on the cable will cause the ATX to act in the same manner as the AT, and I don't want it to.  I do not want it to restart after AC power has gone off and then come back on.

Any thoughts on how to accomplish this?
Thanks

[M3talhead]

Going off my years as an expert satellite electrican, I can tell you you'll need an avocado, a hampster, 3 flux capacitors, and duct tape.




....though I'm not sure what species of hampster you'll actually need.

[SteveJ34]

What's the application for the use of the standalone PS?

Only thing that comes to mind is the use of a Relay switch that in turn will need to be controlled by another source that *does* exhibit the "Do Not Power On when Power is Restored" functionality.

1. If this PS is in a cab that also has a PC which is operating in a manner that you want, ie: no power on when power is restored

 and

2. it fits your design for the secondary ATX PS to be controlled by the first

then you can use a relay switch that is controlled by the 12 volt line from the first PC Power Supply that in turn jumps the pins in the secondary PS to power it on.

As many others have done, I created a single switch power up in this manner using a relay in place of the toggle switch in a power strip.

Such a relay could act as a switch for most anything.....I picked up one at Radio Shack that is rated up to 20amp, 250v IIRC.

I trust the above makes some sense....

[quarterback]

What's the application for the use of the standalone PS?

Without getting too complicated, it's to create a regulated 12v DC (and 5v) power source in my car to power an LCD.

Car 12v is crazy all over the place (7v to 15v to who knows what) and while getting a DC->DC regulator is possible and more energy efficient, it's also more expensive and more limited in functionality.    So my plan is to hook up a power inverter to my car's 12v DC, plug in a mini ATX power supply and grab the stable 12 volts off of that.

That setup will work, but what I would really like is to take advantage of the momentary power switch function of ATX.  That way I'll never subject the PS (or anything attached to it) to an on->off->on surge cycle that can happen when you first start your car.   If the PS automatically switches itself to "off" when the car is shut down, then I'll have to manually turn it on after I start the car.  This is the end result I'm hoping for.

Thanks

[SteveJ34]

Ah, makes sense.

I guess parts like this

http://tinyurl.com/adoyq

are already expecting the incoming 12V to be regulated and don't include the regulator circuitry you would find in an actual DC-DC regulator?

Or what about this: http://tinyurl.com/9zgm9

Doesn't that accomplish what you're after at least for a single 12v circuit?

If yes, I guess you might need more than one to also get the regulated 5v out you want as well.

[beek]

I'm not using a motherboard.

[SteveJ34]

If you wire a momentary switch between pin 14 on the atx connector and ground you will be able to start the power supply manually. 
http://xtronics.com/reference/atx_pinout.htm

That's not been my experience.

As the original author stated, he knows how to "hotwire" the ATX PS to be on. It requires these to be connected, not momentary.

What he's trying to solve is for it to not "power on when power is restored" which as it stands is what it will do without some additional circuitry.

[quarterback]

If you wire a momentary switch between pin 14 on the atx connector and ground you will be able to start the power supply manually.

[Pik4chu]

If you wire a momentary switch between pin 14 on the atx connector and ground you will be able to start the power supply manually.

[wintermute]

It sounds like you've already thought about this, but if I'm thinking correctly, any normal car that is running (with alternator working) should be producing about 14v give or take.

[quarterback]

what this switch you speak of sounds like is possibly a relay... unfortunately I cant think of how to wire it w/o using a switch you must activate manualy. which in my experiences/findings is what people do with carputers anyways to avoid draining the battery.

I'm planning on tapping into the lighter power, so it should only be draining if the key is turned to ACC or the car is running.

What you would do would be hook the car voltage to the coil and to one side of the NO side, so when the car is on, juice is flowing, relay is closed and the device you are powering works.

[coinguy]

Make sure accessory plug turns off when ignition is off.

A SCR (silicon controlled rectifier) will turn on and stay on until power
is removed.  Connect 14 to the (A) anode and Gnd to the cathode (K)
Connect the gate (G) thru a resistor and your pushbutton to (A).
You will need to experiment with the resistor value but 10K should
be a good start.

When the pushbutton is pushed current will start flowing causing
your ATX power supply to turn on.  The SCR has a built-in stay-on
function untill power is removed. (The ignition is turned off)

[quarterback]

You guys are awesome.

[Pik4chu]

You guys are awesome.

[quarterback]

I get a lot of my small electronic parts from either www.mouser.com or www.digikey.com

[coinguy]

You don't need much to do it.

see http://rocky.digikey.com/WebLib/On-Semi/Web%20Data/2N5060.pdf

your local electronics suppliers should have them or a cross-referenced
part.  Ask for counter sales or retail sales.

Sorry Radio Shack doesnt stock anything for the hobbiest
anymore.