FragTek
New member
How To Test Your PSU Rails
Intro
There are 3 main voltage rails on every ATX power supply, it's important to know what the true voltages are for each. Some rails can be monitored from programs such as MBM, Speefan, and the BIOS. However these numbers are all very unreliable. If you rely solely on software for monitoring your voltage rails you are potentially putting your hardware in danger, especially us who have adjustable voltage rails!
Why you CAN'T trust software
At one point I owned an Antec Truepower 550w which would handle pretty much any modern desktop to date. I had no problems with it powering my dual Athlon MP system.
According to Speedfan and the BIOS this however was not the case, giving the following readings:
3.3v Rail - 3.23v
5v Rail - 4.89v
12v Rail - 11.73
All of which seemed far too low for this PSU.
A common misconception is that the BIOS is always right, and whatever it tells you must be the truth. This is far from fact! Let's take a look....
After purchasing a multimeter and testing each rail individually this is what I found:
3.3v Rail - 3.34v
5v Rail - 5.05v
12v Rail - 12.02v
That's the proof right there that the BIOS was blatently lieing to my face about the rail voltages. Think of the damage that could possibly happen to your components due to overvolting if you were to adjust your rails so that they were correct in the BIOS.
What should I do next?
You need to go out to your local hardware store or go online to find yourself a decent multimeter. Any sub $10 multimeter should be accurate enough for our tests. This small investment is worth the price and could save you from damaging expensive components!
Preparing to take your readings
Now that you have your spiffy new multimeter it's time to take a look at what your rails are really running at!
First and foremost we need to setup the multimeter to properly read the voltages we are measuring. This is done by setting the dial on the multimeter to the 20 (DC) mark.
You then need to plug your black probe into the "COM" port of the multimeter and the red probe into the "Voltage Detection" port. Do NOT insert the red probe into the "Current Detection" port as you rish damage to your multimeter.
DO NOT TRY AND MEASURE THE CURRENT/AMPERATE OF YOUR PSU!
By doing this you highly risj frying your PSU and any components that may be connected to it.
Let's continue... While the PC is off, do the following:
- Locate a free 4 pin molex. If you don't have a free 4 pin molex the reading can be taken from the back of the connector, this will work just fine but may be a bit awkward.
- Locate the Auxiliary (AUX) power connector.
Pull these two connectors free from any excessive cable clutter so that they are accessible for your multimeters probes. Remember that this could be an excellent opportunity to get some last minute cable arrangement in
Measuring the Voltages
Alright, let's get down to business! It's important to observer the 3 voltages in all states/phases of the booting and running envorinment. This means setting up the probes before turning the PC on so that you can measure the voltages for the following stages:
- POST
- Boot
- Windows Startup
- System (Idle)
- System (Load)
- Shut down
The biggest flaw of most PSU measuring guides is that they test the PSU externally with minimum load and perhaps only a few fans. This doesn't give any real world indication of how the PSU holds up when powering a voltage hungry computer. That's why my guide teaches you the proper way to measuring your voltage rails by using different levels of load.
Record the voltages at each stage as listed above. Ideally your voltages should not go above or below the rated voltage. Of course no component is perfect thus the ATX spec sheet which sets a parameter for each voltage.
ATX Minimum Specs:
3.3v Rail (Min: 3.14v Max: 3.47v)
5v Rail (Min: 4.75v Max: 5.25v)
12v Rail (Min: 11.4v Max: 12.6v)
Any PSU that falls close to the minimum ATX specs should be replaced. This rail test will also reveal if your PSU has a fluctuation problem, if you have a lot I suggest replacing your PSU even if it stays within min. ATX spec. Remember: Clean, stable voltage is just as important if not more important than having enough voltage.
Measuring the 12v Rail
For this recording you only need the 4 pin molex connector. First insert the red probe into the 12v connector (yellow), and then the black probe into any black ground connector on the molex.
Measuring the 5v Rail
Again, for this recording you will only need the 4 pin molex. This time inster the red probe into the 5v (red) connector and the black probe into any ground connector on the molex.
Measuring the 3.3v Rail
This recording requires the Auxiliary (AUX) connector only, or a combo of the AUX and 4 pin molex together. Inster the red probe into either one of the two 3.3v (orange) connectors on the on the AUX molex. Insert the black probe into any of the black ground connectors on the aux or 4 pin molex connectors.
Using AUX connector only:
Using AUX and 4 pin molex together:
These voltages can also be taken from the ATX connector, you just need to know which wire is which rail.
What have you found out?
Did this test reveal that you need a new PSU, or possibly show that your current PSU is quite a bit better than what software readings were showing? Post your results!
If you need a new PSU, check out PCner2357's guide to help choosing a new PSU: http://www.sysxtreme.com/showthread.php?t=193
I really hope this guide has helped you find out some dirty little secrets you never knew about your PSU If you have any suggestions or found any typo's/errors please let me know so that this guide may be edited and corrected!
-Frag
Intro
There are 3 main voltage rails on every ATX power supply, it's important to know what the true voltages are for each. Some rails can be monitored from programs such as MBM, Speefan, and the BIOS. However these numbers are all very unreliable. If you rely solely on software for monitoring your voltage rails you are potentially putting your hardware in danger, especially us who have adjustable voltage rails!
Why you CAN'T trust software
At one point I owned an Antec Truepower 550w which would handle pretty much any modern desktop to date. I had no problems with it powering my dual Athlon MP system.
According to Speedfan and the BIOS this however was not the case, giving the following readings:
3.3v Rail - 3.23v
5v Rail - 4.89v
12v Rail - 11.73
All of which seemed far too low for this PSU.
A common misconception is that the BIOS is always right, and whatever it tells you must be the truth. This is far from fact! Let's take a look....
After purchasing a multimeter and testing each rail individually this is what I found:
3.3v Rail - 3.34v
5v Rail - 5.05v
12v Rail - 12.02v
That's the proof right there that the BIOS was blatently lieing to my face about the rail voltages. Think of the damage that could possibly happen to your components due to overvolting if you were to adjust your rails so that they were correct in the BIOS.
What should I do next?
You need to go out to your local hardware store or go online to find yourself a decent multimeter. Any sub $10 multimeter should be accurate enough for our tests. This small investment is worth the price and could save you from damaging expensive components!
Preparing to take your readings
Now that you have your spiffy new multimeter it's time to take a look at what your rails are really running at!
First and foremost we need to setup the multimeter to properly read the voltages we are measuring. This is done by setting the dial on the multimeter to the 20 (DC) mark.
You then need to plug your black probe into the "COM" port of the multimeter and the red probe into the "Voltage Detection" port. Do NOT insert the red probe into the "Current Detection" port as you rish damage to your multimeter.
DO NOT TRY AND MEASURE THE CURRENT/AMPERATE OF YOUR PSU!
By doing this you highly risj frying your PSU and any components that may be connected to it.
Let's continue... While the PC is off, do the following:
- Locate a free 4 pin molex. If you don't have a free 4 pin molex the reading can be taken from the back of the connector, this will work just fine but may be a bit awkward.
- Locate the Auxiliary (AUX) power connector.
Pull these two connectors free from any excessive cable clutter so that they are accessible for your multimeters probes. Remember that this could be an excellent opportunity to get some last minute cable arrangement in
Measuring the Voltages
Alright, let's get down to business! It's important to observer the 3 voltages in all states/phases of the booting and running envorinment. This means setting up the probes before turning the PC on so that you can measure the voltages for the following stages:
- POST
- Boot
- Windows Startup
- System (Idle)
- System (Load)
- Shut down
The biggest flaw of most PSU measuring guides is that they test the PSU externally with minimum load and perhaps only a few fans. This doesn't give any real world indication of how the PSU holds up when powering a voltage hungry computer. That's why my guide teaches you the proper way to measuring your voltage rails by using different levels of load.
Record the voltages at each stage as listed above. Ideally your voltages should not go above or below the rated voltage. Of course no component is perfect thus the ATX spec sheet which sets a parameter for each voltage.
ATX Minimum Specs:
3.3v Rail (Min: 3.14v Max: 3.47v)
5v Rail (Min: 4.75v Max: 5.25v)
12v Rail (Min: 11.4v Max: 12.6v)
Any PSU that falls close to the minimum ATX specs should be replaced. This rail test will also reveal if your PSU has a fluctuation problem, if you have a lot I suggest replacing your PSU even if it stays within min. ATX spec. Remember: Clean, stable voltage is just as important if not more important than having enough voltage.
Measuring the 12v Rail
For this recording you only need the 4 pin molex connector. First insert the red probe into the 12v connector (yellow), and then the black probe into any black ground connector on the molex.
Measuring the 5v Rail
Again, for this recording you will only need the 4 pin molex. This time inster the red probe into the 5v (red) connector and the black probe into any ground connector on the molex.
Measuring the 3.3v Rail
This recording requires the Auxiliary (AUX) connector only, or a combo of the AUX and 4 pin molex together. Inster the red probe into either one of the two 3.3v (orange) connectors on the on the AUX molex. Insert the black probe into any of the black ground connectors on the aux or 4 pin molex connectors.
Using AUX connector only:
Using AUX and 4 pin molex together:
These voltages can also be taken from the ATX connector, you just need to know which wire is which rail.
What have you found out?
Did this test reveal that you need a new PSU, or possibly show that your current PSU is quite a bit better than what software readings were showing? Post your results!
If you need a new PSU, check out PCner2357's guide to help choosing a new PSU: http://www.sysxtreme.com/showthread.php?t=193
I really hope this guide has helped you find out some dirty little secrets you never knew about your PSU
If you have any suggestions or found any typo's/errors please let me know so that this guide may be edited and corrected!-Frag
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:bornleet:
