EMMA HS3 Advanced Hardware OutlineWeek #3
Review Homework
Hardware - Computer Power Supply Units (PSU)
Amps, Watts, Volts, and Ohms
Plumbing Example
V=IR, P=VI
Computer Power Supply
Wattage
Appearance
External - Connectors – PC Main, 4-Pin Peripheral, Auxiliary, Serial ATA
Internal - Diodes, Capacitors, Transformers, Heat Sinks
AT vs. ATX – Power-on switch
Laptops – Power Brick
Energy Efficiency – 70-80%, Rest is dissipated as heat
False Advertising
Modular
Troubleshooting
AT12V vs. ATX Power Supplies
AT, ATX, ATX12V
24-Pin Main Power
Multiple 12V Rails
Serial ATA Connectors
Power Efficiency
.PC Power Supplies: More Important Than You Think
(This document available on QUIA class page)
Active vs. Passive Cooling
Power Supply Connectors
Modular Cables and Connectors
High End Supply Example – Gigabyte Odin GT Series
Software Control
Modular Cable Management
Online
What are amps, watts, volts and ohms?
ATX12V vs. ATX Power Supplies
Computer Power Supply (Wikipedia)
Homework
Power Supply Online Quiz
Specify Power Supply on Wish List
PC Power Supplies: More Important Than You Think (Online Document)
What are amps, watts, volts and ohms?
The three most basic units in electricity are voltage (V), current (I, uppercase "i") and resistance (r). Voltage is measured in volts, current is measured in amps and resistance is measured in ohms.
A neat analogy to help understand these terms is a system of plumbing pipes. The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the pipe size.
There is a basic equation in electrical engineering that states how the three terms relate. It says that the current is equal to the voltage divided by the resistance.
I = V/r
Let's see how this relation applies to the plumbing system. Let's say you have a tank of pressurized water connected to a hose that you are using to water the garden.
What happens if you increase the pressure in the tank? You probably can guess that this makes more water come out of the hose. The same is true of an electrical system: Increasing the voltage will make more current flow.
Let's say you increase the diameter of the hose and all of the fittings to the tank. You probably guessed that this also makes more water come out of the hose. This is like decreasing the resistance in an electrical system, which increases the current flow.
Electrical power is measured in watts. In an electrical system power (P) is equal to the voltage multiplied by the current.
P = VI
The water analogy still applies. Take a hose and point it at a waterwheel like the ones that were used to turn grinding stones in watermills. You can increase the power generated by the waterwheel in two ways. If you increase the pressure of the water coming out of the hose, it hits the waterwheel with a lot more force and the wheel turns faster, generating more power. If you increase the flow rate, the waterwheel turns faster because of the weight of the extra water hitting it.
Electrical Efficiency
In an electrical system, increasing either the current or the voltage will result in higher power. Let's say you have a system with a 6-volt light bulb hooked up to a 6-volt battery. The power output of the light bulb is 100 watts. Using the equation above, we can calculate how much current in amps would be required to get 100 watts out of this 6-volt bulb.
You know that P = 100 W, and V = 6 V. So you can rearrange the equation to solve
for I and substitute in the numbers.
I = P/V = 100 W / 6 V = 16.66 amps
What would happen if you use a 12-volt battery and a 12-volt light bulb to get 100 watts of power?
100 W / 12 V = 8.33 amps
So this system produces the same power, but with half the current. There is an advantage that comes from using less current to make the same amount of power. The resistance in electrical wires consumes power, and the power consumed increases as the current going through the wires increases. You can see how this happens by doing a little rearranging of the two equations. What you need is an equation for power in terms of resistance and current. Let's rearrange the first equation:
I = V / R can be restated as V = I R
Now you can substitute the equation for V into the other equation:
P = V I substituting for V we get P = IR I, or P = I2R
What this equation tells you is that the power consumed by the wires increases if the resistance of the wires increases (for instance, if the wires get smaller or are made of a less conductive material). But it increases dramatically if the current going through the wires increases. So using a higher voltage to reduce the current can make electrical systems more efficient. The efficiency of electric motors also improves at higher voltages.
ATX12V vs. ATX PowerSupplies
A Look at the Differences in Power Specifications By Mark Kyrnin, About.com
Introduction Over the years, the base components of computer systems have dramatically changed. In order to standardize the design of the system, specifications standards were developed for desktop computers that define the various dimensions, layouts and electrical requirements so that parts could be easily changed between vendors and systems. Since all computer system require electrical power that is converted from high voltage wall outlets to the low voltage currents used by the components, power supplies have very clear specifications.
AT, ATX, ATX12V? Desktop design specifications have been given a variety of names of the years. The original Advanced Technology or AT design was developed in the early PC years with the IBM compatible systems. As the power requirements and layouts changed, the industry developed a new definition called Advanced Technology Extended or ATX. This specification has been used for many years. In fact it has undergone a large number of revisions through the years to deal with various power changes. Now a new format has been developed over the years called ATX12V. This standard is officially known as ATX v2.0 and above.
The primary differences with the latest ATX v2.2 and ATX v1.3 are:
- Use of a 24-pin Main Power Connector over 20-pin Connector for PCI Express Support
- 6-Pin Aux Power Connector Not Required
- Use of Dual 12V Rails if Greater than 18A
- Serial ATA Power Connectors Required
- Minimum Power Conversion Efficiency
24-Pin Main Power This is the most notable change for the ATX12V standard. PCI Express requires a 75 watt power requirement that was not capable with the older 20-pin connector. To handle this, 4 additional pins were added to the connector to supply the addition power through 12V rails. Now the pin layout is keyed such that the 24-pin power connector can actually be used on older ATX motherboards with the 20-pin connector. The caveat is that the 4 extra pins will reside off to the side of the power connector on the motherboard so be sure there is enough clearance for the extra pins to use on such a board.
Dual 12V Rails As the power demands of the processors, drives and fans keeps growing on the system, the amount of power supplied over the 12V rails from the power supply has also grown. At higher amperage levels though, the ability of the power supply to generate a stable voltage was more difficult. In order to address this, the standard now requires any power supply that produces more than 18A of power for the 12V rail to be split into two separate 12V rails to increase stability. Some high wattage power supplies even have three independent 12V rails for increased stability.
Serial ATA Connectors Even through Serial ATA connectors could be found on many ATX v1.3 power supplies, they were not a requirement. With the rapid adoption of SATA drives, the need for the connectors on all new power supplies forced the standard to require a minimum number of connectors on the power supplies. Older ATX v1.3 units typically only provided two while newer ATX v2.0+ units supply four.
Power Efficiency When the current is converted from the wall outlet voltage to the lower voltage levels needed for the computer components, there is bound to be some waste that is transferred into heat. So, even though the power supply may provide 500W of power, it is actually pulling more current from the wall than this. The power efficiency rating determines how much power is pulled from the wall compared to the output to the computer. The newer standards require a minimum efficiency rating of 70% full power efficiency and a recommended rating of 80%. Very few of the latest power supplies are able to reach the greater than 80% efficiency rating at all wattage levels.
Conclusions When buying a power supply, it is important to buy one that meets all of the power specifications for the computer system. In general, the ATX standards are developed to be backwards compatible with older system. As a result, when shopping for a power supply, it is best to purchase one that is at least ATX v2.01 compliant or higher. These power supplies will still function with older ATX systems using the 20-pin main power connector.
Computer power supply
From Wikipedia, the free encyclopedia
A computer power supply unit (Computer PSU), or Modular Power Supply Unit (MPS) is the component that supplies power to a computer. More specifically, a power supply is typically designed to convert 100-120 V (North America and Japan) or 220-240 V (Europe, Asia and Australia) AC power from the mains to usable low-voltage DC power for the internal components of the computer. Some power supplies have a switch to change between 230V and 115V. Other models have automatic sensors that switch input voltage automatically, or are able to accept any voltage between those limits.
The most common computer power supplies are built to conform to the ATX form factor. The most recent specification of the ATX standard is version 2.2, released in 2004. This enables different power supplies to be interchangeable with different components inside the computer. ATX power supplies also are designed to turn on and off using a signal from the motherboard (PS-ON wire), and provide support for modern functions such as the standby mode available in many computers.
Wattage
Computer power supplies are rated for certain wattages based on their maximum output power. Typical rated wattages range from 200 W to 500 W, although units used by gamers and enthusiasts usually range from 500 W to 800 W, with the highest end units going up to 2 kW for extreme performance computers with multiple processors and graphics cards (ATI CrossFire or NVIDIASLI).
Appearance
External
Most computer power supplies have the appearance of a square metal box, and have a large bundle of wires emerging from one end. A label on one side of the box lists technical information about the power supply, including maximum wattage.
Connectors
Typically, power supplies have the following connectors:
- PC Main power connector (usually called P1): Is the connector that goes to the motherboard to provide it with power. The connector has 20 or 24 pins. One of the pins belongs to the PS-ON wire mentioned above (it is usually green). This connector is the largest of all the connectors. In older AT power supplies, this connector was split in two: P8 and P9. If you have a power supply with 24-pin connector, you can plug it into a motherboard with a 20-pin connector. In cases where the motherboard has a 24-pin connector, some power supplies come with two connectors (one with 20-pin and other with 4-pin) which can be used together to form the 24-pin connector.
- 4-Pin Peripheral power connectors (usually called Molex for its manufacturer): These are the other, smaller connectors that go to the various disk drives of the computer. Most of them have four wires: two black, one red, and one yellow. Unlike the standard mains electrical wire color-coding, each black wire is a ground, the orange wire is +3.3 V, the red wire is +5 V, and the yellow wire is +12 V.
- 4-Pin Floppy drive power connectors (usually called Mini-connector): This is one of the smallest connectors that supplies the floppy drive with power. In some cases, it can be used as an auxiliary connector for AGP video cards. Its cable configuration is similar to the Peripheral connector.
- Auxiliary power connectors: There are several types of auxiliary connectors designed to provide additional power if it is needed.
- Serial ATApower connectors: a 15-pin connector for components which use SATA power plugs. This connector supplies power at three different voltages: +3.3, +5, and +12 volts.
- Most modern computer power supplies include 6-pin connectors which are generally used for PCI Express graphics cards, but a newly introduced 8-pin connector should be seen on the latest model power supplies. Each PCI Express 6-pin connector can output a maximum of 75 W.
Internal
Inside the computer power supply is a complex arrangement of electrical components, including diodes, capacitors and transformers. Also, most computer power supplies have metal heat sinks and fans to dissipate the heat produced. The speed of the fan is often dependent on the temperature, or less often the power load. It may be dangerous to open a power supply even if it is not connected to an electrical outlet, as high voltages may still be present in charged capacitors. However, for most PSU's this can be fixed by unplugging the PSU and then pressing the power-on button, which will drain the capacitors. Still, care should be taken as some PSU's require a load on the output in order to discharge the capacitors fully. Even when the PC is turned off, a PSU will draw some power from the wall, most of it going to power the 5Vsb (standby) rail.
AT vs. ATX
There are two basic differences between old AT and newer ATX power supplies:
- The PC main connectors (see above description of connectors).
- The soft switch. On older AT power supplies, the Power-on switch wire from the front of the computer is connected directly to the power supply. On newer ATX power supplies, the switch goes to the motherboard, allowing it to control the turning off of the system via a message from the operating system.
Laptops
Most portable computers have power supplies that provide 15 to 100 watts. In portable computers (such as laptops) there is usually an external power brick which converts AC power to one DC voltage (most commonly 19v), and further DC-DC conversion occurs within the laptop to supply the various DC voltages required by the other components of the portable computer.
Energy efficiency
Computer power supplies are generally about 70–75% efficient; to produce 75W of DC output they require 100W of AC input and dissipate the remaining 25W in heat. Higher-quality power supplies can be over 80% efficient; higher energy efficiency uses less power directly, and requires less power to cool as well. As of 2007, 93%-efficient power supplies are available. Resonant-transition or quasi-resonant switching regulators could achieve over 90% energy efficiency, and also reduce radio frequency interference.
It's important to match the capacity of a power supply to the power needs of the computer. The energy efficiency of power supplies drops significantly at low loads. Efficiency generally peaks at about 50-75% load. One rule of thumb is that a power supply which is over twice the required size will be much less efficient, and waste electricity.
Small facts to consider
- Common certification marks for safety are the UL mark, GS mark, TÜV, NEMKO, SEMKO, DEMKO, FIMKO, CCC, CSA, GOST R and BSMI. Common certificate marks for EMI/RFI are the CE mark, FCC and C-tick. The CE mark is required for power supplies sold in Europe.
- Life span may be measured in MTBF and should be at least 100,000 hours. Higher MTBF ratings are preferable for longer device life and reliability. Quality construction consisting of industrial grade electrical components and/or a higher speed fan can help to contribute to a higher MTBF rating by keeping critical components cool thus preventing the unit from overheating. Overheating is a major cause of PSU failure.
- There usually is a sticker on the PSU with a list of certifications, the specification, and a warning not to open the enclosure.
- In computer power supplies that have more than one 12V power rail, it is preferable for stability reasons to spread the power load over the 12V rails evenly to help avoid overloading one of the rails on the power supply.
- Multiple 12V power supply rails are separately current limited as a safety feature; they are not generated separately. Despite widespread belief to the contrary, this separation has no effect on mutual interference between supply rails.
- The ATX12V 2.x and EPS12V power supply standards defer to the IEC 60950 standard, which requires that no more than 240 VA be present between any two accessible points. Thus, each wire must be current-limited to no more than 20 A; typical supplies guarantee 18 A without triggering the current limit. Power supplies capable of delivering more than 18A at 12V connect wires in groups to two or more current sensors which will shut down the supply if excess current flows. Unlike a fuse or circuit breaker, these limits reset as soon as the overload is removed.
- Because of the above standards, almost all high-power supplies claim to implement separate rails, however this claim is often false; many omit the necessary current-limit circuitry, both for cost reasons and because it is an irritation to customers. (The lack is sometimes advertised as a feature under names like "rail fusion" or "current sharing".)
- When the computer is powered down but the power supply is still on, it can be started remotely via Wake-on-LAN and Wake-on-Ring or locally via Keyboard Power ON (KBPO) if the motherboard supports it.
- Most computer power supplies have short circuit protection, overpower (overload) protection, overvoltage protection, undervoltage protection, overcurrent protection, and over temperature protection.
- Some power supplies come with sleeved cables, which is aesthetically nicer, makes wiring easier and cleaner and have less effect on airflow.
- There is a popular misconception that a greater power capacity (watt output capacity) is always better. If all else is equal, this is true, but since supplies are self-certified, a manufacturer's claims may be double or more what is actually provided. Although a too-large power supply will have an extra margin of safety, if it is over twice the needed size, it will be less efficient, and waste electricity. Also, computer power supplies generally do not function properly if they are too lightly loaded. Under no-load conditions they may shut down or malfunction.
- Power supplies do not always live up to what they are marketed. Noise can be measured from different distances and at different room temperatures.
False Advertising
The DIY boom has led to power supply manufacturers marketing their products directly to end users, often with grossly inflated specs. Some of the main tricks employed are...