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Problem modding an ATX power supply

Discussion in 'Power Electronics' started by Rob From Pluto, Jun 8, 2015.

  1. Rob From Pluto

    Rob From Pluto

    14
    0
    Feb 9, 2015
    Hi,

    I'm using an ATX power supply to power some 40w leds. I was using several older power supplies, and they work great, but i wanted to buy a new one and clean up the design- it was pretty funny looking with wires sticking out everywhere etc.

    Anyway, it seems to work just fine- i hook everything up, turn the power supply on and the light comes and stays on. But after i turn it off, i can't turn it back on again- the power supply does nothing- no fan, no sounds,and luckily, no smoke.

    I've been reading various forums for a couple of days now and it seems that i'm doing everything right, but still unsure- the power supply was working normally before, and i don't see what could be causing the problem.

    I cut all of the connectors off that go outside the case and separated everything into colors. I only need 12v, so i isolated black and yellow.

    On the old supply, i only needed a black and green soldered together, but i had been reading that i also need to connect a brown to an orange, which i tried but no luck. I also tried putting various resistors between red/black and orange/black, i've read that some power supplies require a dummy load. It doesn't *seem* like it would be a problem though since it turns on and works just fine the first time.

    Does anyone have any ideas? This is a new power supply, and i tested it before cutting wires, was functioning fine (before i got my paws on it anyway:))

    Thanks
     
  2. Kiwi

    Kiwi

    314
    72
    Jan 28, 2013
    What is the make and model of the PSU?

    How long do you have to leave it unplugged before it will restart?

    Have you tried connecting the green to black a few seconds AFTER connecting the mains?

    Do you have a 10Ω resistor connected between red and black?

    Have you joined all the wires of each colour together, eg all the blacks connected to each other?

    Was there a small orange wire joined to another wire in the original plug?

    Will it start up with the LED's disconnected?
     
  3. Rob From Pluto

    Rob From Pluto

    14
    0
    Feb 9, 2015
    I bought it new a couple of months ago but don't see it listed anywhere- it's a cooler master 550w- this is probably the upgraded model

    http://www.newegg.com/Product/Product.aspx?Item=N82E16817171038

    Mine is model rs-550-pcar-n1, that one is RS-550-PCAR-E3

    It needs to stay off for about a minute- i tried less but it won't turn on, i never timed it exactly, but roughly a minute. Also, before i thought it needed to be unplugged from AC, but just leaving its power switch off (with it plugged in) for about a minute works too

    Green to black- no, i didn't know that might be a factor- i have it permanently soldered, that's what most of the PS modding sites say, should i try that?

    Red and black - i have two 6 ohm 10watt resistors that i connected in series between red and black.

    Joining wires- you mean they should be electrically connected? All blacks, all reds, all yellows, etc? I thought they already were on the other ends (where they're soldered to the PS's circuit board?

    Orange wire- i don't know, i cut the connectors off without looking. But.. there *are* four wires of smaller gauge - blue, a grey, a brown and a purple, i don't see a smaller gauge orange anywhere.

    That was a good question, i should have thought of it- i just tried power cycling without any load at all and it's the same- turns on fine once, power down, turn back on, nothing until i leave power off for about a minute.

    Thanks for responding, any suggestions would be fantastic.
     
  4. davenn

    davenn Moderator

    13,322
    1,767
    Sep 5, 2009
    yes they are, so unless you are drawing larger current from which ever rail you are using, That question from kiwi was irrelevant
    his other Q's were all valid tho :)

    Dave
     
  5. Martaine2005

    Martaine2005

    2,406
    632
    May 12, 2015
    I'm not sure about newer psu's but some older ones needed a load on the 5v and 3.3v rails.
    It could be sensing that voltage is on these rails and sensing a fault.
    A possible way to check is to power it on with your load to the 12v then turn it off.
    Then 'carefully' short the caps and then power it back on to see if it powers up without waiting for the minute or so.
    Might work and might not.
     
  6. Rob From Pluto

    Rob From Pluto

    14
    0
    Feb 9, 2015
    Dave- each light is drawing max 2.4A, so i'm thinking i should be safe using a black/yellow for each.

    Martaine- That's what i thought too- mostly older power supplies need the dummy loads, it didn't seem to make a difference as far as symptoms.. You sound like you know what you're doing- i'm not experienced enough to be comfortable shorting things together:) and not sure i'd be able to make use of the results.

    I think you're right- it's sensing a fault, but it just seems odd that it's allowing it to stay on at all.

    I didn't know if there was a suggestion there about grounding green, but i tried this- i disco green from black, hooked everything up and turned the supply on. Obviously nothing happened. Then i grounded the green wire, the light turns on. Disco green, it turns off, shorted green again right away, back on. For reference this is without any dummy loads, and no other mods (purple, brown, gray wires etc are all cut, not jumpered to anything).

    So that works, and i suppose i can wire green to the power switch and use it that way, or do you see any problem with that? I wish i understood the problem though- not knowing what's happening i have to wonder if doing this could cause other problems- i'm hoping to have ten to fifteen of these 40 watt leds hooked up to this ("550w") power supply. I bought a name brand because i figured there would be less problems down the road than a cheap generic,but maybe i shouldn't think so much :). Thank you for the help.
     
  7. Rob From Pluto

    Rob From Pluto

    14
    0
    Feb 9, 2015
    I'm attaching the green and a black to the switch. I attached a picture of the power supply, you can see a small pcb mounted just above the switch and AC power socket- i think i would disco the existing two black wires from the switch, connect them permanently together, then just wire the green to the black, does that sound ok? Fairly straightforward, but i know sometimes there are non-obvious (too a non engineer) things that can go south.

    20150608_193920.jpg
     
    Last edited by a moderator: Jun 9, 2015
  8. davenn

    davenn Moderator

    13,322
    1,767
    Sep 5, 2009
    where is that loose green wire going to

    The black is your mains HOT input through the switch and filter board DONT connect any other cable to that unless you want to cause a bang or zap yourself
     
  9. Rob From Pluto

    Rob From Pluto

    14
    0
    Feb 9, 2015
    Yeah, thanks for saying, what i mean though, i figure i can disconnect both black leads from the switch, solder them together (using shrink tubing of course to keep isolated) and solder the black and green to the switch instead.
     
  10. Rob From Pluto

    Rob From Pluto

    14
    0
    Feb 9, 2015
    Again, for reference for anyone searching for help later on.. I pulled both wires out of the power switch, cut the connectors off and soldered them together, using two layers of heat shrink to keep isolated since this is mains voltage. I wired a green and a black to the switch. The idea was to avoid having to have another "thing" (switch) hanging outside the box, or having to figure out how to mount it, and just using what's already there.

    The point was moot- the original problem is still there- i still need to wait around 60 seconds after powering off before powering back on, so the function that makes it happen must be built into the switch circuitry (there's a PCB that's wired to it).

    I did a fairly nice job of it i think, what a waste of time, but it sure looks pretty:).
     
  11. Rob From Pluto

    Rob From Pluto

    14
    0
    Feb 9, 2015
    On second look, it works after all- before, i was unplugging mains to turn off rather than using the switch- plugging it back in right away wouldn't power it up, i had to wait a minute still. But using the switch to turn it off allowed me to turn it on and off without waiting. It's late, i was forgetting that was the entire point of wiring it up this way.. Not that i understand it completely, but problem solved. Thanks to the people that helped and gave suggestions.
     
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