# [SOLVED] Power Supply starts then stops after manual start up



## johnnyd7 (Oct 3, 2012)

Hi, guys. I took a power supply out of a pc that isn't being used and decided to use it as a power source for my car amp (used inside the house). The power supply is relatively new as it was bought to replace the older one that was in the pc. The power supply was working fine in the pc before I took it out. I shorted the green and black wires and connected all the yellows together and the blacks together and connected those to the amp. When I switch it on, it starts for like half a second then switches off. I tried connecting a 12v fan to it to test it, and the fan just spun briefly then switched off. I noticed that if I disconnect then reconnect the black and green cables, then the process reoccurs every time (switches on then off) What's going on? Any tips and help given will be very much appreciated... 
Thanks in advance.


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## smc217 (Oct 3, 2012)

*Re: Power Supply starts then stops after manual start up*

as far as I recall, green and black wires do not need to be connected. I mean not when its in operation or when its off. What actually starts the PSU, is a short pulse on the wire. So connect them for less then a second (literally touch) and then disconnect.

also some PSUs won't work start if there is no load (but I assume this is not your case)
I might be wrong though, but I hope that helps. Let me know anyway.


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## visseroth (Oct 25, 2010)

*Re: Power Supply starts then stops after manual start up*

Actually, I have to correct smc. I have used a power supply for similar situations and the green and the black wire do need to be shorted out. This acts as a switch for the power supply just as on a relay when the coil is lit the relay kicks on.
If the power supply is kicking off it is either due to to much of a load or a short is being detected.
Check the specs of the power supply on the 12v rail and see if the amperage meets the requirements of the amp. If it is close then it is to close and you're putting to much of a load on the power supply.
Now because you are using the power supply for something that it is not intended I can't guarantee the safety of either you, the power supply or the equipment you're trying to power but you may be able to take another power supply and tie them in parallel to get more current.
However, I again warn you, do this at your own risk.


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## johnnyd7 (Oct 3, 2012)

*Re: Power Supply starts then stops after manual start up*

Thanks for the replies, guys. If the power supply isn't meeting the requirements of the amp, then why does it not work when I use a normal 12v fan as a tester? To me it feels like the power supply needs something extra to keep it running, I don't know. Maybe another two wires needs to be shorted or something. I seen that there's a grey wire called Power OK, but when I checked online, no one used that when doing a similar thing with the car amp like I'm doing.


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## visseroth (Oct 25, 2010)

*Re: Power Supply starts then stops after manual start up*

That is a good question. Usually when I've used a power supply for similar situations and it turns off like that it usually means bad power supply. That the power supply is detecting a internal fault and is protecting what it is connected too.
Have you tried another power supply?


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## johnnyd7 (Oct 3, 2012)

*Re: Power Supply starts then stops after manual start up*

I don't quite have another to mess about with. The thing is that it did work before though. It was working before I took it out of the pc which was yesterday. So I don't think it's an internal fault... Any other ideas as to what it could be?


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## visseroth (Oct 25, 2010)

*Re: Power Supply starts then stops after manual start up*

Try connecting just the motherboard connector to a motherboard and see if it stays on then.


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## johnnyd7 (Oct 3, 2012)

*Re: Power Supply starts then stops after manual start up*

Lol, I cut the connector off already. The article I read said I could do it as it wouldn't be needed anymore. I've definitely learned from that mistake.


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## pctoxicated (Sep 22, 2012)

*Re: Power Supply starts then stops after manual start up*

Can you upload a pic of how you have it wired?


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## johnnyd7 (Oct 3, 2012)

*Re: Power Supply starts then stops after manual start up*

View image: 20121004 102937


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## visseroth (Oct 25, 2010)

*Re: Power Supply starts then stops after manual start up*

just out of curiosity, try disconnecting all your 12v lines and see what it does.


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## MPR (Aug 28, 2010)

*Re: Power Supply starts then stops after manual start up*

Modern switching power supplies require a load or they will shut off. Better PSUs provide this load internally but cheaper ones may not. Also, some PSUs may require a load on the red wires (5 V) and even the orange wires (3.3 V) as well as on the yellow wires (12 V). The cheapest PSUs can burn out under no load operations, where others will shut down immediately to protect the circuitry.

What is the make and model number of your PSU -- it's specifications (if available) may shed some light on the minimum load required for operation. Also, tape off the unused wires so none are shorting out (and it doesn't have to be against a ground either -- any voltage difference between two wires can cause a current flow).


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## johnnyd7 (Oct 3, 2012)

*Re: Power Supply starts then stops after manual start up*

Ok, I did that. Same thing happens. Tried connecting the fan to the red and orange cables, same thing happened...


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## johnnyd7 (Oct 3, 2012)

*Re: Power Supply starts then stops after manual start up*

@MPR, will try that now.


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## pctoxicated (Sep 22, 2012)

*Re: Power Supply starts then stops after manual start up*

wire the green and black to the rest of the blacks


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## johnnyd7 (Oct 3, 2012)

*Re: Power Supply starts then stops after manual start up*

Ok @MPR, got the same results. Specs can be found here: View image: 20121004 130213 It's a pretty cheap ps, which is why I'm experimenting with it. @pctoxicated, I will be needing some of the blacks if I were to connect it up to the amp...


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## pctoxicated (Sep 22, 2012)

*Re: Power Supply starts then stops after manual start up*

can you upload a pic of where you plan connecting it too please.


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## MPR (Aug 28, 2010)

*Re: Power Supply starts then stops after manual start up*

I couldn't find much info on XGR PSUs.

Most of the people who are converting computer PSUs to lab supplies are using a 10 ohm, 10 W resistor on one of the 5 V (red) wires to provide the necessary minimum load.


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## johnnyd7 (Oct 3, 2012)

*Re: Power Supply starts then stops after manual start up*

Ok, so I just reconnected all the wires to their respective plugs, and it is working. My hands are now sore. So mpr, you think I need the resistor? Where can I get one?


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## johnnyd7 (Oct 3, 2012)

*Re: Power Supply starts then stops after manual start up*

Ok guys, thanks for all the help. I found out what the problem was. After much analysis of the wiring, I have a solution: For those in the same boat as I was that's reading this, if you already cut the 20/24 pin molex connector make sure the brown wire is connected to an orange wire, then you'll be good to go  When the molex connector isn't cut, the two orange and brown wires are already joined, so that's why the others weren't having the problem I was.


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## Tyree (May 10, 2009)

Glad you found the problem and thanks for posting back.


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## MPR (Aug 28, 2010)

Glad you got your supply up and running, and good find noting that your PSU had a 3.3 V sense wire that was not connected.

The article below is a good read for those who are interested in converting a computer PSU for another purpose. The quoted section explains the voltage sense wires.



> Voltage Sensing
> 
> If your PS has two wires attached to the same pin on the motherboard power connector, orange +3.3 VDC and a brown sense wire on Pin 11 for example, then these two wires should be joined when you make your conversion. Some power supplies may also have sense wires running to the +5 VDC and +12 VDC connector pins. If there are multiple sense wires, then they will usually be of the same color as the primary supply wire, but of a lighter wire gauge. These sense wires will also terminate in a different location on the PS printed circuit board than the heavier supply lines. As with the +3.3 sense wire, these additional wires should also be connected to the corresponding supply lines. Failure to complete these connections may result in your power supply not latching into a Power_On mode when switched on.


http://reprap.org/wiki/PCPowerSupply


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## visseroth (Oct 25, 2010)

Ahh! Interesting. See I never cut the motherboard plug off. I always jumped the green and black with a piece of a paperclip so there for i never knew about any other joined wires. A bit strange I think because if the circuits needed to be connected you would think the manufacturer would do this in the power supply.
Good to know and thank you for posting back your find.


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