Help me install a LED Power Switch on my ATX PSU please!

[slapaham]

Okay... I'm building a supergun project and it uses a mini ATX PSU. However, it works as soon as you plug it into the mains. I'd like to have control as to when it powers on and so I want to install a small switch. I also want some indication of when it is definitely powering on so a switch with an incorporated LED seems like a good idea!

I found this one Ebay with the accompanying animation...



When I look at my ATX there are 2 wires coming from the 3 prong mains socket. I can't remember the colours off hand but I think they might be green and black? I can check if needs be! Anyway, I'm a bit confused as to where I connect these and also what would be the best way of powering the LED.

Here's the specific auction page for more details -
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=120549602603&ssPageName=STRK:MEWAX:IT#ht_1049wt_1167

Please correct me if this is wrong but I'm assuming the green and black (if thats what the colours were!) from the 3 prong socket are connected this way -

green to plus on switch
black to ground on switch
then for the bulb I'm thinking perhaps get a molex cable, take a 12v wire from it and crimp it to 'a' on the switch to power the bulb? I see that as the molex connection will kick in when there's power going to the ATX this makes sense?

Or am I totally barking up the wrong tree? Please someone let me know, so I can either a) buy it and get a step closer to finishing this project or b) rethink how I'm going to achieve this!
 

[Ed_McCarron]

I'm guessing no.  It takes the voltage in on the + terminal, and when 'on' connects it to the 'A' terminal.  The LED is across 'A' and Gnd.  If you follow your plan, it sounds like you'll be tying 12v to the green wire when switched on.  If you could isolate the LED from the 'a' terminal this could work.

Perhaps see if you can either:

find a switch with an isolated LED?

buy the switch and see if you can get at the LED leads?

Find a DPDT switch to isolate the two?

IIRC, the green carries 5v at minimal current -- you pull it to gnd to start the PS.

[lilshawn]

this is not what you are looking for. if you are going to switch the "Mains" (AC power) to the power supply you should (read MUST) use a "double pole" switch to disconnect both the live and the neutral wires from the power supply.

ALSO

your led light on the switch will only run on 12 volts.... your going to be trying to run it on line voltage (way more than 12)

try to find a switch specifically designed to switch mains voltage.

[slapaham]

Thanks guys... back to the drawing board... I'll post up when I find something else but because I have to say I'm a little lost atm!

[Ed_McCarron]

Hm, what country are you in, slapaham?

Heres a 120v lighted switch if you want to actually switch the mains:

http://www.allelectronics.com/make-a-store/item/LRS-133/ON-OFF-LIGHTED-ROCKER-SWITCH-120-VAC/-/1.html

But, thats not how I interpreted your original post.  I figured you want to leave the AC on and switch the ATX ps via the green to ground option.

Perhaps just a standard switch with an external LED/resistor hung across the 12v/gnd rails of the power supply?

[Franco B]

Perhaps just a standard switch with an external LED/resistor hung across the 12v/gnd rails of the power supply?

Thats what I was thinking.

You could use one of those LED holders if it makes mounting easier.

[XCVG]

this is not what you are looking for. if you are going to switch the "Mains" (AC power) to the power supply you should (read MUST) use a "double pole" switch to disconnect both the live and the neutral wires from the power supply.

Why? I've actually seen a power supply where only one line is switched. There's probably a good reason that I haven't remotely thought of though, knowing me.

Also, yeah, that switch won't work.

[RandyT]

this is not what you are looking for. if you are going to switch the "Mains" (AC power) to the power supply you should (read MUST) use a "double pole" switch to disconnect both the live and the neutral wires from the power supply.

Why? I've actually seen a power supply where only one line is switched. There's probably a good reason that I haven't remotely thought of though, knowing me.

Yeah, light switches in your home only break one wire of the AC, so I don't know why you would need a double pole switch to go this route.

But Ed is the only one here who seems to have understood the OP.  What he said.

RandyT

[slapaham]

A bit muddled as to what should have been concluded here! Probably me being dumb!

Is it that it would probably be best to get a switch for the power and then get a separate LED powered from molex.

Thanks for all the responses guys - much appreciated!

[RandyT]

Ok, I'm confused suddenly as well and maybe the other folks were with you if you are indeed talking about AC.  But I get a feeling that you are using some words here that don't really reflect the situation you are asking about.

If you have an ATX power supply, you shouldn't have any view of the AC power, unless you have taken the cover off.  If you are talking about a similar power supply for arcade cabinets, these may have wire terminals for the AC in and the other voltages going out, but this would not be an "ATX" supply.

Without being able to accurately convey your situation, you need to take some pictures and post them if you want good advice.

The thing that causes the confusion is your reference to green and black wires, which on an actual ATX supply, will turn power on and off.  But a 3 prong "mains" socket sounds like AC (and that you have the cover off of the supply).

If you are only powering a PCB and some lights, you should find out why the ATX PSU is coming on immediately (probably green and black jumpered as described above) and that is where you would put your switch.  Then you could run any type of indicator LED ligthing from the +5 or +12 output of the supply.  

Please take a picture so we know what you are asking.

RandyT

[slapaham]

Hi Randy

Thanks for the post. I will take some photos tomorrow of the project. You're spot on with most of what you have said though. The project case is TIGHT so I have removed the case from the ATX. It is a standard PC ATX and isn't like an arcade PSU.

Anyway, as I said before, I'll take some photos (best way I reckon! ) so that is far clearer as to what I want to achieve!
 

[slapaham]

Okay, here's a photo!




The bit mounted is the 3-pronged 'kettle lead' socket for the power cable. The colours of the wires going to it are actually blue and brown NOT green and black like I said before.

When it comes to powering a power LED, I will probably just buy a molex extender and cut the end off and either wire it to the 5 or 12v (which ever it requires!)

[Ed_McCarron]

Okay, here's a photo!




The bit mounted is the 3-pronged 'kettle lead' socket for the power cable. The colours of the wires going to it are actually blue and brown NOT green and black like I said before.

Ah.  Blu/Brn/Grn is European power cord colors.  You -are- messing with the mains side of things.

The green/black combo we were all fixating on is what an ATX power supply uses to power itself up.  You leave the mains power on, and switch the low voltage.

In your case, Brown is the hot wire.  Technically, you COULD switch this lead and make it all work, but if you've got the low voltage option on the ps, why not use it?  Can you take a pic of the end of that spiralwrapped bundle of wires?

And, yes, a lot of PC PSU's switched hot and neutral, I assume that was purely a safety thing incase the outlet was wired wrong -- if the polarity was reversed, you'd be switching the neutral and I could see it causing some problems in the right circumstances.

[slapaham]

OK, this is starting to make a little more sense to me now... finally!

So what you're saying is I have 2 options... either to install a switch on the power cable (brown, blue, yellow/green) side of things, or, I could install it on the black and green cables on the ATX connector (which is at the end of the bundled wires you were referring to).

It would be more preferable for me if I could install the switch on the brown, blue and yellow and green cabling for positioning, etc.

As this switch is mains-capable - would it be suitable for the job? -
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=360215105349&ssPageName=STRK:MEWAX:IT#ht_2682wt_941

It has an LED built in... and 4 prongs according to the auction description. I take it 2 of these prongs would be wired to Live and Earth to complete the circuit to power the ATX on and off and the other 2 prongs would be for powering the LED?

Sorry if I'm getting confused again but I'm pretty new to switches and simple circuits.

[lilshawn]

the reason i say that you should use a double pole switch is because there is a chance that:

a: the wiring in the wall socket is incorrect
b: the wiring in the plug (especially if it's been replaced) is incorrect
c: the cabinet wiring is incorrect.

any ONE of these wiring errors can result in a switched live and neutral wire.

most manufacturers attach the neutral of the mains voltage wire to the chassis, so in case of a short, the circuit breaker in the house blows instead of the metal case of your supply becoming hot (energized) this becomes especially true with 2 wire plugs (non-grounded)

should any of the above (a,b,c) be incorrect, disconnecting what you THINK is the "live" wire via a switch, would leave the case energized with "live" electricity. and touching it would suck. Bad. Like REALLY bad, since now you are the powers return to earth ground.


you may switch only the live wire to break the electrical connection to your power supply, but be aware there is a risk involved.

[slapaham]

Based on what you have said, would it be a sensible idea to simply have a switch on the green 'ON' wire on the ATX then? As this is the cable that dictates the powering up then if a switch is placed on it, it will dictate on and off. If this is all true and a sensible solution, I guess I would need to couple it with a black 'neutral' wire to complete the switch circuit?

Thanks for your help!

[Ed_McCarron]

Based on what you have said, would it be a sensible idea to simply have a switch on the green 'ON' wire on the ATX then? As this is the cable that dictates the powering up then if a switch is placed on it, it will dictate on and off. If this is all true and a sensible solution, I guess I would need to couple it with a black 'neutral' wire to complete the switch circuit?

Thanks for your help!

Yes.  Leave the mains alone, put a switch across the green and black wires (on the ATX output plug) and you should be good.  Hang a standalone LED (with the appropriate current limiting resistor) across 5v or 12v and DC common.

Avoid calling the dc common 'neutral.'  Thats more of an AC term and electricians will call you nasty names. 

[slapaham]

  to electricians!

Thanks for the advice chap. This project is starting to get more of a challenge now (not because of what was discussed here!), so I have a feeling it's only going to get more difficult from here on out!

P.S. Just to clarify, this ISN'T an arcade machine build! (but it is arcade-related!)