# Power Supply Testing



## bill of oz

how do you properly test if a power supply is working or not?

does anybody have a link to an article or video that describes how to properly test if a power supply is working or not?


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## jamesd1981

Here you go  - http://pcsupport.about.com/od/toolsofthetrade/f/powersupplytest.htm


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## Darren

You can also perform the paper clip test. 

Bend a paper clip into a U shape and with the PSU *unplugged* insert one end into the ATX connection where the green cable is and the other end into one of the black cable connectors (there are several, just pick one). With the PSU powered off plug it back in and hook it up to a fan and switch the PSU on. If the fan spins up it is at least outputting some power. If it is then go on to the suggestions listed above.

Paper clip test is good to just test if a PSU is totally dead.


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## beers

Also keep in mind that the multimeter or PSU tester only checks voltage.  A lot of times you'll have a unit that can provide an OK voltage but can't deliver sufficient amperage (the other half of the wattage equation) and will either buckle to not boot the PC or cause issues under load.

Most commonly you'll see shops swap with a known-good PSU to more quickly verify if the previous unit was indeed faulty.


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## StrangleHold

bill of oz said:


> how do you properly test if a power supply is working or not?
> 
> does anybody have a link to an article or video that describes how to properly test if a power supply is working or not?


 
 Like said, you can do the paper clip text just to see if it works. But it tells you nothing about when its under a load.


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## The VCR King

I like my power supply (1000 watt Cougar CMX) because if there is a power surge it keeps my PC on and just reboots it.


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## Darren

The Blue Beast said:


> I like my power supply (1000 watt Cougar CMX) because if there is a power surge it keeps my PC on and just reboots it.



What.

No.

If your power surges due to lightning or something it'll probably just fry your computer if it's plugged in at the time. PSU's don't have that kind of tech built in (at least not yours).

If the power flickers or something like that your computer will lose power for just enough time to shut it down and it will automatically reboot, I think most if not all computers do that. Mine's done it a few times during storms.


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## voyagerfan99

Denther said:


> If the power flickers or something like that your computer will lose power for just enough time to shut it down and it will automatically reboot, I think most if not all computers do that. Mine's done it a few times during storms.



Everything you have said is correct except for this part. Power settings in BIOS determine whether your computer resumes or stays off after loss of power. The settings specifically are:

-Power On
-Last State
-Stay Off


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## Darren

voyagerfan99 said:


> Everything you have said is correct except for this part. Power settings in BIOS determine whether your computer resumes or stays off after loss of power. The settings specifically are:
> 
> -Power On
> -Last State
> -Stay Off



Interesting. I guess now that I think about it I have seen that before when in the BIOS. Is this on by default for most motherboards?


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## voyagerfan99

Denther said:


> Interesting. I guess now that I think about it I have seen that before when in the BIOS. Is this on by default for most motherboards?



The default for most motherboards is Stay Off.


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## G80FTW

The Blue Beast said:


> I like my power supply (1000 watt Cougar CMX) because if there is a power surge it keeps my PC on and just reboots it.



If there was an actual "surge", the last thing you would want is for your computer to be on in the first place (let alone plugged in).  And to that, what would be good about it keeping the PC on anyway if its going to reboot? Your data would have still been lost either way....

So had that been true, it would be pointless.


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## Darren

voyagerfan99 said:


> The default for most motherboards is Stay Off.



Interesting. In the computers I've worked with they tend to just restart. Thanks for clearing that up.


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## johnb35

Yeah, its always best for it to stay off after a power failure.  A few times here the power has gone off and came back on and with in a few seconds went off again for a few minutes.  It's times like this if you know a bad storm is coming then unplug it anyway.  One time the power went off here and when it came back on, my pc wouldn't turn back on.  I was like uh oh, not a good sign.  So happens the outage loosened the power cable going into the power supply connection.  I was lucky.


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## Darren

I normally unplug my computer during storms anyway but this is good info. Thanks. :good:


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## spirit

Denther said:


> I normally unplug my computer during storms anyway but this is good info. Thanks. :good:



I'm a badass and leave it plugged in. So far so good, but you might not want to risk it.


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## beers

The Blue Beast said:


> I like my power supply (1000 watt Cougar CMX) because if there is a power surge it keeps my PC on and just reboots it.



That's not a feature, rofl.  The system lost enough wattage to quit processing but not to turn off completely.  

Some PSUs with higher capacitance can keep your PC on for a second or so depending on load.  Otherwise just get a UPS.


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## Jamebonds1

It would be better if you do multmeter.  I have expesive multmeter but it will give me accurate.  10 dollar multmeter is very inaccurate so avoid it! (most of them)  My experinced step.

1 Step, unplug everything that connection to PSU. 

2 Step, short between green and black wires. 

3 Step, plug in any one of external fan as load power.  

4 Step, plug in power cable and turn on PSU.  

5 Step, check on yellow, red and orange wire color with your multmeter.  12V, 5V, 3.3V.  It should be in +/- 5% volt range.  

NOTICE:  You have to do math.  
EX:  (voltage * (Precent of range/100)) + voltage; 
(12V * (+/- 5%/100)) + 12V;  
(12V * (+/- 0.05)) + 12V;  
+/- 0.6V +12V;
0.6V + 12V = Max 12.6V and -0.6 + 12V = Min 11.4V; 
Max 12.6V and Min 11.4V.


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## Okedokey

Jamebonds1 said:


> It would be better if you do multmeter.  I have expesive multmeter but it will give me accurate.  10 dollar multmeter is very inaccurate so avoid it! (most of them)  My experinced step.
> 
> 1 Step, unplug everything that connection to PSU.
> 
> 2 Step, short between green and black wires.
> 
> 3 Step, plug in any one of fan as load power.
> 
> 4 Step, plug in power cable and turn on PSU.
> 
> 5 Step, check on yellow, red and orange wire color with your multmeter.  12V, 5V, 3.3V.  It should be in +/- 5% volt range.
> 
> NOTICE:  You have to do math.
> EX:  (voltage * (Precent of range/100)) + voltage;
> (12V * (+/- 5%/100)) + 12V;
> (12V * (+/- 0.05)) + 12V;
> +/- 0.6V +12V;
> 0.6V + 12V = Max 12.6V and -0.6 + 12V = Min 11.4V;
> Max 12.6V and Min 11.4V.



A fan will provide next to no load to test 12V rail.   Therefore your test is completely meaningless.


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## Jamebonds1

Okedokey said:


> A fan will provide next to no load to test 12V rail.   Therefore your test is completely meaningless.



I think I remember that some your comment is not always true and were meant to create issue.  

That prove you're wrong about the external fan with no current amp.  
http://media.digikey.com/pdf/Data Sheets/Sunon PDFs/80x80x25mm.pdf

And this,

https://www.youtube.com/watch?v=5FWXgQSokF4

It is necessary step to getting reliable voltage read and prevent from damaging PSU.  Fan was used as load.  

So unless I was wrong, please don't waste my time with unsource comment.  I'm not stupid as I was.


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## G80FTW

Jamebonds1 said:


> I think I remember that some your comment is not always true and were meant to create issue.
> 
> That prove you're wrong about the external fan with no current amp.
> http://media.digikey.com/pdf/Data Sheets/Sunon PDFs/80x80x25mm.pdf
> 
> And this,
> 
> https://www.youtube.com/watch?v=5FWXgQSokF4
> 
> It is necessary step to getting reliable voltage read and prevent from damaging PSU.  Fan was used as load.
> 
> So unless I was wrong, please don't waste my time with unsource comment.  I'm not stupid as I was.



Well....sadly he does actually have a point.  A case fan will not pull any significant power from the system.  0.2 amps is almost nothing.  While it is a load technically speaking, I personally wouldnt consider it enough of a load to use for testing.

Pulling 0.2 amps from a line that is made to supply 25A + is hardly a load for any power supply.  You would be better off using a few HDDs.


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## Jamebonds1

G80FTW said:


> Well....sadly he does actually have a point.  A case fan will not pull any significant power from the system.  0.2 amps is almost nothing.  While it is a load technically speaking, I personally wouldnt consider it enough of a load to use for testing.
> 
> Pulling 0.2 amps from a line that is made to supply 25A + is hardly a load for any power supply.  You would be better off using a few HDDs.



Yeah.  I'm not buy that.  I'm not sure where you get that information from, but there is no source that external fan is not better way to test voltage.  0.2 amp is more than enough to test a voltage.  That would give you reliable read and prevent from being damaging.  The voltage is depend on PWM chip (voltage adder).  I built switch mode power supply, so I know how they work.  Math are pain in neck.


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## voyagerfan99

Jamebonds1 said:


> Yeah.  I'm not buy that.  I'm not sure where you get that information from, but there is no source that external fan is not better way to test voltage.  0.2 amp is more than enough to test a voltage.  That would give you reliable read and prevent from being damaging.  The voltage is depend on PWM chip (voltage adder).  I built switch mode power supply, so I know how they work.  Math are pain in neck.



It's pure logic. Just because you can pull 1/5th of an amp doesn't mean you can pull more than that.


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## Jamebonds1

voyagerfan99 said:


> It's pure logic. Just because you can pull 1/5th of an amp doesn't mean you can pull more than that.



What do you mean?


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## Okedokey

A PSU's ability to provide stable voltage regulation diminishes as you change the percentage load.  Loading a 12V rail with 2A or less (a fan) is completely meaningless and pointless.  The only way to fully test stability, noise etc is to load it up 50% or more, and even then, it wont have any effect on the other voltage rails.

Secondly most PSU's these days run fine without a load and will reliably give you a 12V or any voltage read.

Your test is pointless for determining vdroop or regulation limits.


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## Jamebonds1

Okedokey said:


> A PSU's ability to provide stable voltage regulation diminishes as you change the percentage load.  Loading a 12V rail with 2A or less (a fan) is completely meaningless and pointless.  The only way to fully test stability, noise etc is to load it up 50% or more, and even then, it wont have any effect on the other voltage rails.
> 
> Secondly most PSU's these days run fine without a load and will reliably give you a 12V or any voltage read.
> 
> Your test is pointless for determining vdroop or regulation limits.



I'm not buy that.  Your argument is pointless without source website.  So where is your source?  

PS: precent is voltage not amp.


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## Okedokey

Jamebonds1 said:


> I'm not buy that.  Your argument is pointless without source website.  So where is your source?
> 
> PS: precent is voltage not amp.



I don't need a source mate, as the equation for %regulation is a function of load.  So without a load, your tests are virtually meaningless beyond "the psu switches on".

Load regulation of a constant-voltage source is defined by the equation:

%{Load Regulation} = 100% X {V_{min-load} - V_{max-load}} / {V_{nom-load}}

So yeah, any basic understanding of switching mode powers supplies would provide you with the reason why loading is important.


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## Jamebonds1

Okedokey said:


> I don't need a source mate, as the equation for %regulation is a function of load.  So without a load, your tests are virtually meaningless beyond "the psu switches on".
> 
> Load regulation of a constant-voltage source is defined by the equation:
> 
> %{Load Regulation} = 100% X {V_{min-load} - V_{max-load}} / {V_{nom-load}}
> 
> So yeah, any basic understanding of switching mode powers supplies would provide you with the reason why loading is important.



Good lucky at try to get me believe without source.


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## Okedokey

Jamebonds1 said:


> Good lucky at try to get me believe without source.



Time and time again, you've been proven to not understand psus... im not going to bother as you're struggling to even type a sentence.


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## Jamebonds1

Okedokey said:


> Time and time again, you've been proven to not understand psus... im not going to bother as you're struggling to even type a sentence.



Then don't bother to proven me wrong without source next time.  I know you use wikipedia to given math which is why I don't believe you.


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## Okedokey

Dude, i have an electronic engineering degree, so I really don't need to reference anything.

But here you go:



> The DC output voltages shall remain within the regulation ranges shown in Table 2 when measured at the load end of the output connectors under all line, *load*, and environmental conditions. The voltage regulation *limits shall be maintained under continuous operation for any steady state temperature and operating conditions specified in Section 5*.



and Section 3.2.1 where voltage regulation measurements and tolerances are measured at *peak load*.

http://www.formfactors.org/developer\specs\ATX12V_PSDG_2_2_public_br2.pdf


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## Jamebonds1

Okedokey said:


> Dude, i have an electronic engineering degree, so I really don't need to reference anything.
> 
> But here you go:
> 
> 
> 
> and Section 3.2.1 where voltage regulation measurements and tolerances are measured at *peak load*.
> 
> http://www.formfactors.org/developer\specs\ATX12V_PSDG_2_2_public_br2.pdf



I already proved that information and I told that voltage read should be in range of +/- 5%.  Go read my post again very careful.


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## voyagerfan99

Okay guys, get over it and move on.


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## Okedokey

Jamebonds1 said:


> I already proved that information and I told that voltage read should be in range of +/- 5%.  Go read my post again very careful.



Ok, let this be my last post on the matter then i give up.

The role of a PSU is to provide a constant voltage for a variable load.  The 5% tolerance is a minimum and maximum variance over different loads.  Measuring or testing this at just above minimum load provides absolutely no evidence that a PSU can sufficiently maintain voltage regulation at any other load.  That is why the design standard specifies all tolerances (e.g. ATX standards) to be measured at 100% load, peak temperature.  As both these things affect the voltage regulation.



> Ideally, the output of most power supplies should be a constant voltage. Unfortunately, this is difficult to achieve. ...factors that can cause the output voltage to change. [is]...* is a change in the load resistance. In complex electronic equipment, the load can change as circuits are switched in and out. *
> 
> These variations in load resistance tend to change the applied dc voltage because the power supply has a fixed internal resistance. If the load resistance decreases, the internal resistance of the power supply drops more voltage. *This causes a decrease in the voltage across the load*.
> 
> Many circuits are designed to operate with a particular supply voltage. When the supply voltage changes, the operation of the circuit may be adversely affected. *Consequently, some types of equipment must have power supplies that produce the same output voltage regardless of changes in the load resistance or changes in the ac line voltage. This constant output voltage may be achieved by adding a circuit called the VOLTAGE REGULATOR at the output of the filter. *
> 
> LOAD REGULATION
> 
> A commonly used FIGURE OF MERIT for a power supply is its *PERCENT OF REGULATION*. The figure of merit gives us an indication of how much the *output voltage changes over a range of load resistance values*. The percent of regulation aids in the determination of the type of load regulation needed. Percent of regulation is determined by the equation:
> 
> 
> 
> 
> 
> 
> This equation compares the *change in output voltage* at the two *loading extremes to the voltage produced at full loading*. For example, assume that a power supply produces 12 volts when the load current is zero. If the output voltage drops to 10 volts when full load current flows, then the percent of regulation is:
> 
> 
> 
> 
> 
> 
> Ideally, the output voltage should not change over the full range of operation. *That is, a 12-volt power supply should produce 12 volts at no load, at full load, and at all points in between*. http://www.tpub.com/neets/book7/27j.htm



Therefore your specified test with simply a small load (fan) will provide no information beyond the latching circuit works as it is not testing for any real-case scenario.


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## Jamebonds1

Okedokey said:


> Ok, let this be my last post on the matter then i give up.
> 
> The role of a PSU is to provide a constant voltage for a variable load.  The 5% tolerance is a minimum and maximum variance over different loads.  Measuring or testing this at just above minimum load provides absolutely no evidence that a PSU can sufficiently maintain voltage regulation at any other load.  That is why the design standard specifies all tolerances (e.g. ATX standards) to be measured at 100% load, peak temperature.  As both these things affect the voltage regulation.
> 
> 
> 
> Therefore your specified test with simply a small load (fan) will provide no information beyond the latching circuit works as it is not testing for any real-case scenario.



Go read voyagerfan's post again.  That mean you need stop too.  I can keep post as long as it is not going damage or read incorrect, unless I'm told to stop post about how to test PSU with multimeter.  So get it over.  Voyagerfan is right, it is time to stop fight.


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## StrangleHold

Using a case fan to test a 12V rail, all you will find out is if its stable at a .25amp/3W. I guess if all you want to push with it is a case fan then your great. If you have a issue with a rail. Its voltage and wattage can fluctuate widely depending on how much load your putting on it. I've replaced many power supplies with this same issue. If you truly want to test it, you should at least put a 50% or more load.


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## voyagerfan99

Jamebonds1 said:


> Go read voyagerfan's post again.  That mean you need stop too.  I can keep post as long as it is not going damage or read incorrect, unless I'm told to stop post about how to test PSU with multimeter.  So get it over.  Voyagerfan is right, it is time to stop fight.



He proved his point. And that's fine. You're the only one still going on about it.


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## G80FTW

StrangleHold said:


> Using a case fan to test a 12V rail, all you will find out is if its stable at a .25amp/3W. I guess if all you want to push with it is a case fan then your great. If you have a issue with a rail. Its voltage and wattage can fluctuate widely depending on how much load your putting on it. I've replaced many power supplies with this same issue. If you truly want to test it, you should at least put a 50% or more load.



I used to use older power supplies to run car amplifiers inside my house that I used as my home theater (since car audio is relatively cheaper than home audio).  And I can tell you, with the volume turned up (the last PSU I used was rated at 30A on the 12V) it would drop to around 10v before shutting off.  The first time I attempted this, I actually melted the original wire in the power supply (as Im sure I was pushing alot more than 30A through it) so I upgraded the wire to 8awg and it ran alot better.

But yes, higher loads will certainly have an effect on the voltage. That goes for ANY electrical device. The more amperage you attempt to draw from a power source, as the power source struggles to maintain that amperage it will eventually start losing voltage to do so.


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