Problem w/new ATX power supply modded as gen purpose power supply - Page 1
Forum section: electronics / repair

author: RobFromEarth
author_rank: Regular Contributor
timestamp: June 06, 2015, 09:52:17 am
content: I have a problem with an ATX power supply that i modified to use as a power supply for some lights, i was hoping someone might be able to suggest what the problem could be. I've used the same lights with several other modded power supplies with no problems, but i wanted a new one (more dependable).I bought this power supply new:http://www.newegg.com/Product/Product.aspx?Item=N82E16817171038(actually the model is rs-550-pcar-n1 but this is very close, apparently it's been updated)The other power supplies i had just been splicing the green with black (to power on without CPU) and cutting only the yellow/black wires as i needed, but i wanted a cleaner mod this time, so i cut *all* of the wires (well, all of them that go outside the box), soldered the green to a black, and separated all of the yellow and black wires to use (i don't need anything except 12v).The symptoms- when i power up with lights attached, everything works just as it should. After powering down, i can't power up again until i unplug power from the supply for a minute or so. I checked inside to make sure i didn't leave any bare wires, nothing is shorting to something it shouldn't etc, but i don't see any problems.My guess is the supply is disabling itself to protect itself.Do some of the wires that i cut need to be connected? I cut everything that leads to the outside of the case- all of the power cables, mother board connector, everything, soldered the green to a black, use the yellow and blacks for power and isolated all of the rest (put electrical tape on the ends to protect)I turned the supply off, unplugged, turned it back on (to drain excess voltage), i wanted to check that there's no residual power so hooked a meter to yellow/black. I accidentally put the meter on continuity and measured continuity between yellow and black, that's not good i think? I measured between the case and black, continuity. The same between yellow and case.Any suggestions?Thank you!Rob

author: Ian.M
author_rank: Super Contributor
timestamp: June 06, 2015, 10:01:36 am
content: Many ATX PSUs require a minimum load on the 5V and 3.3V rails. Without any load, the reservoir caps will retain their charge for some time and it may be detecting voltage on the outputs when its meant to be off as a fault.The smart move when re-purposing an ATX PSU is to use compatible connectors rather than hacking the wiring. That makes it simple to swap out the PSU or to return it under warranty. Once you start clipping wires you are S.O.L. if it doesn't work the way you expect.

author: RobFromEarth
author_rank: Regular Contributor
timestamp: June 06, 2015, 10:28:34 am
content: I never intended on returning it anyway, once i made sure it was functional.. The minimum load i thought was only for older supplies- is there a way to verify that's the problem without trying it? If there's something messed, i'm afraid i might fry it if i keep turning it on. The symptoms don't sound dangerous? Continuity between yellow and black wires doesn't sound.. safe..

author: Ian.M
author_rank: Super Contributor
timestamp: June 06, 2015, 10:48:10 am
content: Large reservoir caps + Schottky rectifiers (with their very low Vf) in the PSU mean that getting a continuity reading between 12V and 0V/chassis even without a fault is quite possible, depending on the test voltage your meter uses. If the PSU outputs a stable 12V into a load without overheating or other misbehaviour, there is almost certainly nothing wrong with it.I would suggest testing into a cheap resistive dummy load - e.g. car bulbs. A headlight bulb is typically 55W per filament and will draw about 4 1/2A. Stick it in a ceramic mug or similar and use clip leads. The worst that can happen is that the PSU blows up, but if its faulty, you certainly don't want to risk your actual lights on it and you cant send it back so what have you got to loose?Whether on not load resistors will help is something you will have to find out for your self. If you don't have suitable ones, try 10W car bulbs. Solder wires on if you have to and if it works, get some wirewound resisors to replace them.

author: RobFromEarth
author_rank: Regular Contributor
timestamp: June 06, 2015, 11:29:25 am
content: Thanks, that sounds reasonable, but pretty much is what i'm doing because the led lights are 40watt. Everything works fine, all lights on, stay on steady (no dimming or blinking), i turn the supply off, then when i turn it back on, no power at all/supply fan doesn't kick on. It stays that way until i unplug AC from supply for a minute or so. Does there still need to be a load on the 5v line as well as the 12v that's powering the led? It just didnt seem the problem given symptoms. It's consistent- every time the led powers up just fine, after i pow cycle the PS there's no power until i disco AC for a minute or so.

author: Psi
author_rank: Super Contributor
timestamp: June 06, 2015, 11:38:10 am
content: Some ATX psus have a extra wire going to some ATX pins. It's used to monitor the voltage at the end of the cable for better regulation.If you cut off all the wires you may have inadvertently cut this feedback

author: Ian.M
author_rank: Super Contributor
timestamp: June 06, 2015, 11:46:08 am
content: As I said earlier, without a load on the other rails, residual voltage on them may be detected as a fault at startup. Its up to *YOU* to test this hypothesis by adding loads and seeing if it can then be powered off and back on without a long wait.

author: RobFromEarth
author_rank: Regular Contributor
timestamp: June 06, 2015, 11:50:12 am
content: Ian- Thanks, i wasn't getting that part- it's the first thing i'll check this morning.Psi- i didn't know that, do you happen to know if there's a standard color wire or location that i can look for? That sounds very possible too.

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 06, 2015, 01:37:35 pm
content: try connecting the green wire to chassis (gnd earth), not to black wire.

author: RobFromEarth
author_rank: Regular Contributor
timestamp: June 07, 2015, 05:13:11 am
content: I finally got a 55w car bulb together , that didn't change anything, both turn on when i first plug everything in, stay on until i cut power. Once i cut power i can't turn on again until i leave the PS unplugged for a minute or so.Green wire to chassis- Same results.. It seems like PSI's suggestion might be worth looking into, but i haven't found anything in ATX pinouts that helps- does anyone know what it might be called, or what color it might be?Thanks

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 07, 2015, 05:27:23 am
content: What exactly does "cut power" mean?Does that mean you disconnect the green control wire from ground?Or do you have the green control wire hard-soldered to ground?

author: RobFromEarth
author_rank: Regular Contributor
timestamp: June 07, 2015, 05:39:23 am
content: The power supply has a power switch, i meant flipping the switch to off. The green and black are soldered.Thanks

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 07, 2015, 05:41:43 am
content: Quote from: RobFromEarth on June 07, 2015, 05:39:23 amIt is not clear that is a valid method. I would try momentarily grounding the green wire to turn it on.

author: RobFromEarth
author_rank: Regular Contributor
timestamp: June 08, 2015, 04:22:31 am
content: I had already tried that by someone's suggestion, but no change.I started looking at all of the colors i cut- The yellow is for +12v, the only voltage i need. The red is for +5v, i don't need 5v either, likewise for orange (+3.3v)I did try using a dummy load on both 5v and 3.3v, no effect.Here are the symptoms again. I have a 40w LED connected to +12v (yellow/black). It powers on just fine, i can leave it on for as long as i want, but if i shut it off (using the power supply's built in switch), it won't turn on again (using the same switch) until i unplug the AC cord from the supply for about a minute.Here are the colors that i'm unsure of, i've been reading a lot but so far haven't found a solution- All of the wires i clipped (except yellow and black) are bundled in a rubber band. There are 6 orange (3.3), 8 8red (5), a blue, a grey, a brown and a purple. All of them are smaller gauge, but who can read letters that small, i don't have a microscope with me.This page:http://web2.murraystate.edu/andy.batts/ps/DESIGN_GUIDE.HTMDescribes remote sensing, last paragraph seems most relevant, but it's not clear if it's talking about the brown or orange, and if orange, well i thought orange was for 3.3v..This pagehttp://web2.murraystate.edu/andy.batts/ps/POWER_OK.HTMTalks about the grey wire, i'm not sure, but i think it's irrelevant in this case, it seems to say that the computer uses it, not the supply itself, but i'm not sure if it's talking about the computer's post, or if it's saying that modern power supplies have their own POST.have been reading for a couple of days, those are just two pages that seem like they could be relevant, i haven't started with purple or blue yet. I suppose i could simply connect all four to see if the problem resolves itself, but since i'm not using it for a PC, there's nothing to connect them to. Anyway the point is to learn, since the newer supplies apparently function a bit differently than older ATX supplies. Most all of the nearly dozen pages i've read about modding an ATX as a gen purpose PS don't mention anything about needing to have any of these connected to anything, aside from a dummy load on 3.3/5v (is it always both, or sometimes one or the other?)Thanks for any guidance.Rob

author: RobFromEarth
author_rank: Regular Contributor
timestamp: June 08, 2015, 04:35:32 am
content: The page at:http://web2.murraystate.edu/andy.batts/ps/DESIGN_GUIDE.HTMSays:The +3.3 VDC remote sensing wire (brown or orange) is connected directly to the orange +3.3 VDC at pin 11 of the power connector (pin 13 if a 2x12). The sense wire will usually be of a lighter gauge (22 AWG) than the power wires (16 or 18 AWG) and its purpose is to monitor the voltage at the connector in order to provide feedback for voltage compensation by the supply.(2nd to last paragraph). I'm not sure i have it right, i believe it's saying the smaller gauge brown (there is one on my supply) is connected to one particular orange wire- i thought an orange was an orange (as far as the wires leading out of the case go- there are other orange wires that have nothing to do with it).I've read a ton over the past two months as i've had time, and have been focusing for about two days on this and haven't found anything that helps. I had been using older atx supplies for years without a problem.

author: RobFromEarth
author_rank: Regular Contributor
timestamp: June 08, 2015, 06:47:49 am
content: I've connected brown wire 3.3v remote sensing. I still don't understand why it needs to be connected, but i see it listed in a few places- if it's there, it should be connected to an orange wire (direct, no load).I also have dummy loads- 10watt, from 6 ohm to 20 ohm on 5v and 3v rails.None of this has made any change- it still powers on just fine, after powering down, it won't power on again until letting it stay off for a minute or so.From reading, most places say the gray (power OK) isn't needed since only the computer uses it for post.

author: RobFromEarth
author_rank: Regular Contributor
timestamp: June 09, 2015, 02:27:33 am
content: I wasn't able to find a solution here but thought i'd post here for reference for anyone else having the same problem.I have all of the cables that lead to outside of case cut. I have only a yellow and black hooked to a 40watt led (2.4A max draw). I have nothing else hooked up on the supply (no dummy load, no sense wire etc). I plug in/turn on supply. Obviously nothing happens. I short green to black, system turns on. I disco green, turns off, i connect green to black right away, success, everything turns on.Somehow the PS is sensing a fault condition most likely, noone's been able to help me nail it down, maybe they've engineered it to keep people from using it this way. But i probably can wire green/black to the power switch and use it that way..

author: Ian.M
author_rank: Super Contributor
timestamp: June 09, 2015, 02:52:22 am
content: It may be a design feature so it does a full shutdown if power is briefly interrupted. If the incoming power is unstable it wouldn't do a hard drive much good if the PSU output pulses on and off rapidly. A 1 minute lockout prevents that.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 09, 2015, 03:03:01 am
content: So use a small toggle switch between the green control wire and black ground. I don't understand what is the problem here?

author: RobFromEarth
author_rank: Regular Contributor
timestamp: June 09, 2015, 05:34:18 am
content: The problem is i can't turn them back on unless i wait a minute, sometimes there isn't a minute spare to wait for the projects i'm using these with. The point of buying a name brand PS was to avoid funky problems down the road, but blegh, maybe i was thinking too much, this has too many cool features.Ian, that would make sense, thanks for saying, another cool feature to play with. I was thinking i'd disconnect both of the blacks from the main switch and solder together (using shrink tubes to isolate of course- it's a mains cable) and solder the green and black to the switch instead, unless you see a potential problem with that. Obviously those mains wires need heavy insulation to keep anything from contacting.

author: Ian.M
author_rank: Super Contributor
timestamp: June 09, 2015, 11:12:51 am
content: Not a good idea. Leave the mains switch as is, where it is at the back and fit a subminature toggle switch with gold plated contacts at the front for the low voltage power on signal. Its a matter of maintaining safety clearances so the toggle switch should be over the isolated section of the board + once a switch has been used for mains into anything with large bulk decoupling caps, it will always have slightly burnt contacts which wont be reliable 'dry' switching a low current low voltage control signal.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 09, 2015, 12:27:03 pm
content: Quote from: RobFromEarth on June 09, 2015, 05:34:18 amThen you are trying to force a kludge to work in a way it was not designed for. You need a proper bench supply, but you are trying to jury-rig a PC power supply and complaining that it works properly.