Power Supply
From Extreme Overclocking
Contents |
Power Supply Units (PSU)
Intro to electricity
Volts - Difference in charge between two locations
Amps - Amps or amperes is, put simply, the measure of electrical current flow. To describe it in more detail. An ampere is a constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum, would produce between these conductors a force equal to 2 x 10–7 newton per metre of length. Note also that one ampere is equal to one coulomb per second.
Coulombs - Is the unit of electric charge. It is defined in term of amperes. Coulombs is found by the formula Q = It. Q is the charge in couloumbs, I is the current in amperes and t is time in seconds.
Watts - Amps * Volts = Watts; Total measure of power.
Testing a PSU
Jump starting a PSU
ATX power supplies will not turn on unless they are connected to a motherboard, but an easy modification will allow it to be easily started without a motherboard attatched. The pins connected to the green and black wires (Pins 14 and 15) of the ATX connector need to be connected with a small piece of wire, or even a small paperclip. As soon as they lose contact, the PSU will shut off. Here is a picture of the two pins to be connected:
However, it should be noted that since power supplies are designed to run with a load, you should have some load, at least on the 5v rail for safe operation. There are several products made which both jump the two pins to allow standalone starting as well as provide a load to the power supply to prevent damaging it due to lack of load.
Testing the rails
Modern ATX Power supplys output three main voltages. For optimal performance of the computer, as well as good overclocks, the three voltages (+5v, +12v, and +3.3v) should remain fairly close to what they are supposed to be. For instance, the 12v line should be at or around 12v. Often times it is neccessary to test the rails of a power supply to rule it out in troubleshooting. Many software programs, as well as BIOS offer voltage readings, but they are generally not right and should not be trusted. However voltages can be easily checked with a digital multimiter that can be obtained for around $20 at radioshack.
First, set the dial on the multimeter to the 20v setting.
Find the connectors shown in this picture:
Important Links
Powering Your PC: Truths and Misconceptions - A Guide To Power Supplies
How To Test Your Power Supply Rails - By TheCleaner
Power Supply Testing Methodology at EXTREME Overclocking (Lots of extra info)
