This is a compilation from various forums and sites which are mentioned at the bottom.
Many enthusiasts invest thousands of rupees into building a state-of-the-art custom PC. They buy the fastest processors, biggest hard drives, top of the line video cards, but then skimp when it comes to choosing a power supply to bring their behemoth to life. Spending Rs.50000 on your dream PC and Rs.300 on a generic power supply is not only bad judgment, it could be potentially damaging to the PC components if the PSU is unable to deliver clean current and stable voltages.
A good quality and properly sized power supply is essential for maintaining overall system stability and component longevity. The precise voltage and current demands of today's high-end hardware will only continue to increase. It is worthwhile to plan for excess power capacity now, so that future component upgrades will not require a surprise (and potentially costly) power supply upgrade too.
This chart describes how many watts each component requires to work and which line it uses from the PSU. The Wattages listed below are maximum peak wattage for each component.
The total amount this calculator figures is for all devices running at peak utilization. It is important to bear in mind that this amount will never be reached under typical operation.
*Some motherboards use the +5v for RAM (ex. DFI infinities)
(From PC Power & Cooling)
Using these two PSU Calculators mentioned below, you can find out the total power requirements of your computer.
eXtreme PSU Calculator v1.2
JS Custom PCS
As a PC performs different tasks, it will consume different amounts of power on different rails, everything is in a constant state of flux. However, on average the 12V rail is the most important for a modern PC. So always pay attention to the 12V rating, regardless of what the overall PSU rating is (Some PSUs have an oversized 5V rail, which pumps up the total power rating, but does the end user little good in a modern PC).
These are some helpful links to help you know everything you wanted to know about PSU.
A to Z PSU List with Rating High/Med/Low from Tech Support Forums (Techenclave)
CoolerMaster - Official Pricing (Techenclave)
Power Supply Fundamentals & Recommendations (Silentpcreview)
Power Distribution (Silentpcreview)
Power Supply Guide for Today's & Tomorrow's Computers (Extremeoverclocking.com)
The Ultimate "Do I need a 24pin PSU ?" thread (Anandtech)
Everyone is welcome to add on to this topic...............
[break=What are Watts?]
What are Watts?
To understand this we need to understand volts, and amps:.
'Volts' are the potential difference of electrical energy between two points
'Amps' (or current) is the rate of flow of electrons
A 'Watt' is a measurement of 'volts' * 'amps', the ability to move electrons over 1amp a second
Henceforth, we will refer to 'Watts' as 'w', 'volts' as 'v', and 'amps' as 'a'
What are Rails?
A rail is the delivery system for power. On a modern PSU these rails are divided into +3.3v, +5v, +12v, -5v and -12v. The important ones for us to look at are the positive rails. These will be specified to deliver an amount of amps per rail. Seeing as w = v * a. This tells us the output in watts of the PSU.
EXAMPLE:
Watts =+3.3v rail*30a = 100w
Watts =+5v rail *30a = 150w
Watts =+12v rail*25a = 300w
Adding them together gives us a power output of 550w. There are caveats to this, which we will examine later.
Dual +12V Rails:
The modern trend of components drawing off the +12v rail, has led to the introduction of multiple +12 rails, which are easier and cheaper to produce that bigger rails, but more importantly easier to keep stable and cool. There was the suggestion to also to give the cpu a completely independent rail for cleaner voltage, however for economic reasons no PSU has two fully independant (ie seperate transformer taps and regulators) 12V rails. In most cases, one rail (12V2) is dedicated entirely to the cpu, and the other rail (12V1) runs all the other components (video card(s), hard drives etc). Increasingly more power supplies (especially EPS) are coming out with 3 or even 4 rails, to handle computers that need more than 20A 12V capacity for components, and/or multiple cpu systems.
More useful guides on Dual Rails-
Power Supply Unit
Dual +12V Rails
A 20 Pin and 24 Pin ATX connector
A 20 Pin ATX connector on a 24 Pin Motherboard
[break=Power Supply Standards]
Power Supply Standards
The predominant standard at the moment, with the exception of a "small form factor" PC, is ATX 12v. This features a 20-pin connector to the motherboard, and in addition to the ATX standard, a 4-pin +12v connector. This is due to modern CPU using the +12v rail, whereas a Pentium III operated across +5v. The standard also sets out standards for power fluctuation, which must not exceed (+ or -)5% per positive rail. ATX 12v version 2, released in Feb 2003, requires SATA connectors. We are now at version 2.01. A history of versions can be found here.
An additional standard exists - ATX EPS 12v - for server and workstation. This specifies a 24-pin main connector and an 8-pin +12v connector for the motherboard. With the move to socket 775, Intel has updated the main motherboard connector to 24-pin.
A new standard on the horizon is BTX - Balanced Technology Extended - which amongst other things will address issues of heat and airflow by placing components in a 3D plane rather than the existing 2D, there are other advantages, but they are beyond the scope of this article. Some power supplies are already on the market claiming to be BTX ready, and may be a way to future proof your investment.
Negative Rails
You will notice that the negative rails on your PSU are very week when compared to the positive rails. This is due to them being there more or less for legacy reasons. Although a 20 pin ATX motherboard connector has pin 12 -12v and pin 18 -5v, they're generally not used by the motherboard. They are there for:
ISA cards
Serial port or LAN
Older FDD
Hold Up Time
This is the amount of time in milliseconds that a PSU can hold output at the correct voltages after a loss of input power. This allows your PC to carry on running, despite a brief interruption in AC power, the higher the figure the better. The ATX specification requires a minimum of 17ms.
[break=What is PFC?]
What is PFC?
PFC is Power Factor Correction. Power Factor is a measurement of how effectively power is being used, and is expressed as a number between 0 and 1, with the high number meaning that power is being used effectively.
Two types of load are placed on the PSU, resistive; power converted into heat, light motion, i.e. working power. Inductive; sustaining an electric field in a transformer or motor, also called reactive power. Together, working and reactive power make up apparent power. Power factor is a measurement of the ratio between working and reactive power, or working power/reactive power. The ideal is for the two to be the same, i.e. a PF of 1.
There are two types of PFC, passive and active. Passive uses a capacitive filter on the AC input to maintain the inductive load, without an addition of power. Active uses a circuit to match the resistive and inductive loads.
Every PSU sold in the Europe is now required to have PFC, although when I bought mine, I knew nothing about this, and the dealer supplied me with a US model, complete with 110V settings. If you have a non PFC PSU, always make sure that the voltage is set correctly for your region as damage will result if not. This is another benefit of PFC; it automatically senses and adjusts to the input voltage.
The common misconception is, that PFC will lead to lower electricity bills. This is not true unless you are a commercial user who is charged by Volt Amps and PFC, rather than KW/hr.
The benefits are to the environment, keeping power clean, reducing harmonics. . For a more detailed look at PFC, see Adrian's Rojak Pot. Please note if you have a room full of PCs, e.g. a folding farm a high PFC (lowering current required) will allow you to connect more PCs, to a single circuit.
Peak Vs Continuous Power
Continuous power is what the PSU is capable of delivering all the time. Peak is for short bursts - e.g. 60 seconds. To run a PSU above its continuous power rating for an extended period of time, will result in damage, so make sure when specifying to get the correct figure.
Noise Level
This will be measured in db. It is very important to match this to the environment you will be using your PC in. In a noisy office environment, 30db may be fine. In a living room of your house, 30db will cause arguments between you and your partner. As a general rule, a PSU with a 120mm fan should be quieter than one with a higher pitched 92mm or 80mm fan. You need to be looking for fan speed to be adjustable according to PSU load/temperature. As a PSU works harder, it will heat up, and cause the fans to work harder. As an example, a PSU may work at 20db when at up to 70% capacity, going up to 32db as it nears 95%. Take this into account when working out which power supply you want. If you need 300W, and to get it you need to operate the PSU at 85%, then you may be better off going for the next model, that can supply it at 70%, and all things being equal, do so more quietly.
As for totally a silent PSU, with passive cooling - based on all reviews I have read, I cannot recommend them for a BE type system, on a cost performance basis. They are very expensive, so much so that you could get a real high end active cooling solution, and under-stress it as described above. A passive PSU is extreme in its own way, and thus only recommended if you live in a library.
Water-cooling is another way to silence your PSU. There are a few articles published on the web on 'how to' water-cool a PSU. For the sake of interest, I will include a couple of links at the end of this guide. However this is not something I can recommend, due to the charge that a PSU will hold for days. It is dangerous, and good luck to you if you embark on such a project!
Adjustable Pots
These allow you to adjust the voltage to each rail, for instance if the +12v rail is reading low at +11.5v, this could cause some system instability. Remember, the ATX standard allows for a variation of +-5%. Voltage can be adjusted back up to +12v by use of the 'pots', or potentiometers. This is quite an advanced feature, so you need to make sure you know what you are doing, and I would suggest further reading, if you are an enthusiast.
Source
Power Supply Tutorial by Quad Master
Many enthusiasts invest thousands of rupees into building a state-of-the-art custom PC. They buy the fastest processors, biggest hard drives, top of the line video cards, but then skimp when it comes to choosing a power supply to bring their behemoth to life. Spending Rs.50000 on your dream PC and Rs.300 on a generic power supply is not only bad judgment, it could be potentially damaging to the PC components if the PSU is unable to deliver clean current and stable voltages.
A good quality and properly sized power supply is essential for maintaining overall system stability and component longevity. The precise voltage and current demands of today's high-end hardware will only continue to increase. It is worthwhile to plan for excess power capacity now, so that future component upgrades will not require a surprise (and potentially costly) power supply upgrade too.
This chart describes how many watts each component requires to work and which line it uses from the PSU. The Wattages listed below are maximum peak wattage for each component.
The total amount this calculator figures is for all devices running at peak utilization. It is important to bear in mind that this amount will never be reached under typical operation.
*Some motherboards use the +5v for RAM (ex. DFI infinities)
(From PC Power & Cooling)
Using these two PSU Calculators mentioned below, you can find out the total power requirements of your computer.
eXtreme PSU Calculator v1.2
JS Custom PCS
As a PC performs different tasks, it will consume different amounts of power on different rails, everything is in a constant state of flux. However, on average the 12V rail is the most important for a modern PC. So always pay attention to the 12V rating, regardless of what the overall PSU rating is (Some PSUs have an oversized 5V rail, which pumps up the total power rating, but does the end user little good in a modern PC).
These are some helpful links to help you know everything you wanted to know about PSU.
A to Z PSU List with Rating High/Med/Low from Tech Support Forums (Techenclave)
CoolerMaster - Official Pricing (Techenclave)
Power Supply Fundamentals & Recommendations (Silentpcreview)
Power Distribution (Silentpcreview)
Power Supply Guide for Today's & Tomorrow's Computers (Extremeoverclocking.com)
The Ultimate "Do I need a 24pin PSU ?" thread (Anandtech)
Everyone is welcome to add on to this topic...............
[break=What are Watts?]
What are Watts?
To understand this we need to understand volts, and amps:.
'Volts' are the potential difference of electrical energy between two points
'Amps' (or current) is the rate of flow of electrons
A 'Watt' is a measurement of 'volts' * 'amps', the ability to move electrons over 1amp a second
Henceforth, we will refer to 'Watts' as 'w', 'volts' as 'v', and 'amps' as 'a'
What are Rails?
A rail is the delivery system for power. On a modern PSU these rails are divided into +3.3v, +5v, +12v, -5v and -12v. The important ones for us to look at are the positive rails. These will be specified to deliver an amount of amps per rail. Seeing as w = v * a. This tells us the output in watts of the PSU.
EXAMPLE:
Watts =+3.3v rail*30a = 100w
Watts =+5v rail *30a = 150w
Watts =+12v rail*25a = 300w
Adding them together gives us a power output of 550w. There are caveats to this, which we will examine later.
Dual +12V Rails:
The modern trend of components drawing off the +12v rail, has led to the introduction of multiple +12 rails, which are easier and cheaper to produce that bigger rails, but more importantly easier to keep stable and cool. There was the suggestion to also to give the cpu a completely independent rail for cleaner voltage, however for economic reasons no PSU has two fully independant (ie seperate transformer taps and regulators) 12V rails. In most cases, one rail (12V2) is dedicated entirely to the cpu, and the other rail (12V1) runs all the other components (video card(s), hard drives etc). Increasingly more power supplies (especially EPS) are coming out with 3 or even 4 rails, to handle computers that need more than 20A 12V capacity for components, and/or multiple cpu systems.
More useful guides on Dual Rails-
Power Supply Unit
Dual +12V Rails
A 20 Pin and 24 Pin ATX connector
A 20 Pin ATX connector on a 24 Pin Motherboard
A 24 Pin ATX connector on a 24 Pin Motherboard
PCI-e power connector for PCI-e graphics cards - supplies additional power to the more power hungry PCI-e graphics cards
[break=Power Supply Standards]
Power Supply Standards
The predominant standard at the moment, with the exception of a "small form factor" PC, is ATX 12v. This features a 20-pin connector to the motherboard, and in addition to the ATX standard, a 4-pin +12v connector. This is due to modern CPU using the +12v rail, whereas a Pentium III operated across +5v. The standard also sets out standards for power fluctuation, which must not exceed (+ or -)5% per positive rail. ATX 12v version 2, released in Feb 2003, requires SATA connectors. We are now at version 2.01. A history of versions can be found here.
An additional standard exists - ATX EPS 12v - for server and workstation. This specifies a 24-pin main connector and an 8-pin +12v connector for the motherboard. With the move to socket 775, Intel has updated the main motherboard connector to 24-pin.
A new standard on the horizon is BTX - Balanced Technology Extended - which amongst other things will address issues of heat and airflow by placing components in a 3D plane rather than the existing 2D, there are other advantages, but they are beyond the scope of this article. Some power supplies are already on the market claiming to be BTX ready, and may be a way to future proof your investment.
Negative Rails
You will notice that the negative rails on your PSU are very week when compared to the positive rails. This is due to them being there more or less for legacy reasons. Although a 20 pin ATX motherboard connector has pin 12 -12v and pin 18 -5v, they're generally not used by the motherboard. They are there for:
ISA cards
Serial port or LAN
Older FDD
Hold Up Time
This is the amount of time in milliseconds that a PSU can hold output at the correct voltages after a loss of input power. This allows your PC to carry on running, despite a brief interruption in AC power, the higher the figure the better. The ATX specification requires a minimum of 17ms.
[break=What is PFC?]
What is PFC?
PFC is Power Factor Correction. Power Factor is a measurement of how effectively power is being used, and is expressed as a number between 0 and 1, with the high number meaning that power is being used effectively.
Two types of load are placed on the PSU, resistive; power converted into heat, light motion, i.e. working power. Inductive; sustaining an electric field in a transformer or motor, also called reactive power. Together, working and reactive power make up apparent power. Power factor is a measurement of the ratio between working and reactive power, or working power/reactive power. The ideal is for the two to be the same, i.e. a PF of 1.
There are two types of PFC, passive and active. Passive uses a capacitive filter on the AC input to maintain the inductive load, without an addition of power. Active uses a circuit to match the resistive and inductive loads.
Every PSU sold in the Europe is now required to have PFC, although when I bought mine, I knew nothing about this, and the dealer supplied me with a US model, complete with 110V settings. If you have a non PFC PSU, always make sure that the voltage is set correctly for your region as damage will result if not. This is another benefit of PFC; it automatically senses and adjusts to the input voltage.
The common misconception is, that PFC will lead to lower electricity bills. This is not true unless you are a commercial user who is charged by Volt Amps and PFC, rather than KW/hr.
The benefits are to the environment, keeping power clean, reducing harmonics. . For a more detailed look at PFC, see Adrian's Rojak Pot. Please note if you have a room full of PCs, e.g. a folding farm a high PFC (lowering current required) will allow you to connect more PCs, to a single circuit.
Peak Vs Continuous Power
Continuous power is what the PSU is capable of delivering all the time. Peak is for short bursts - e.g. 60 seconds. To run a PSU above its continuous power rating for an extended period of time, will result in damage, so make sure when specifying to get the correct figure.
Noise Level
This will be measured in db. It is very important to match this to the environment you will be using your PC in. In a noisy office environment, 30db may be fine. In a living room of your house, 30db will cause arguments between you and your partner. As a general rule, a PSU with a 120mm fan should be quieter than one with a higher pitched 92mm or 80mm fan. You need to be looking for fan speed to be adjustable according to PSU load/temperature. As a PSU works harder, it will heat up, and cause the fans to work harder. As an example, a PSU may work at 20db when at up to 70% capacity, going up to 32db as it nears 95%. Take this into account when working out which power supply you want. If you need 300W, and to get it you need to operate the PSU at 85%, then you may be better off going for the next model, that can supply it at 70%, and all things being equal, do so more quietly.
As for totally a silent PSU, with passive cooling - based on all reviews I have read, I cannot recommend them for a BE type system, on a cost performance basis. They are very expensive, so much so that you could get a real high end active cooling solution, and under-stress it as described above. A passive PSU is extreme in its own way, and thus only recommended if you live in a library.
Water-cooling is another way to silence your PSU. There are a few articles published on the web on 'how to' water-cool a PSU. For the sake of interest, I will include a couple of links at the end of this guide. However this is not something I can recommend, due to the charge that a PSU will hold for days. It is dangerous, and good luck to you if you embark on such a project!
Adjustable Pots
These allow you to adjust the voltage to each rail, for instance if the +12v rail is reading low at +11.5v, this could cause some system instability. Remember, the ATX standard allows for a variation of +-5%. Voltage can be adjusted back up to +12v by use of the 'pots', or potentiometers. This is quite an advanced feature, so you need to make sure you know what you are doing, and I would suggest further reading, if you are an enthusiast.
Source
Power Supply Tutorial by Quad Master
