Power Supplies Flashcards
Electricity Basics
Volts: Is the pressure.
Amperage: Is the size of the pipe.
Volts * Amps = Watts
(DC) Direct Current: Only flows in one direction.
(AC) Alternating Current: Rapidly switches directions.
AC runs long distances very well.
DC power gets things done more efficiently.
The Power Supply
ATX power supplies are all listed in max Watts.
On a power supply: Yellow wire is 12 volts and red wire is 5 volts.
ATX Power supplies come with the option of switching between 110 and 220 volts.
P1 connector: There are two sizes of P1 connectors, 20 and 24 pin. This is the main power for the motherboard.
P1 connector 20 pins is for older and low power ATX systems.
Supplementary Power Connector: These are either 4 or 8 pin. Some motherboards are ok with only using a 4 pin even though they have an eight pin slot.
PCI Express power connectors: Used exclusively for PCI express video cards.
Sata Power Connectors: Sata’s are used for hard drives, and optical drives.
Mini Connectors: Not used much any more.
Molex Power Connector: Older connector. Used to be used for a lot of stuff but now it is used for secondary equipment like fans.
Nice Power Supplies and Features
Modular Power Supply: Comes with female plugs on the back to plug in the cables that you need.
Small Form Factor Power Supplies: These are smaller in size but the connectors are very similar to a standard ATX power supply.
Choosing a Power Supply
Efficiency: Power supplies do not take the voltage and the ampls and turn it perfectly into watts. A good power supply has an efficiency rating north of 90%. Bad once are as low as 50%.
Try to not use anything less than 82-85% efficiency.
Rails: Power supplies take 110 or 220 volts AC and turn it into 12V, 5V, and 3.3V DC. Rails are electrical circuitry that isolate different type of power outputs.
The most important power on your system is the 12 Volts.
Make sure to know the amount of power being output on each rail of a power supply.
On a good power supply you will see 2, 3, and 4 rails.
Efficiency should be quoted at operating temperature.
Troubleshooting Power Supplies
Power supplies are the most likely component to fail in a system.
Power Supplies either die slow or catastrophically.
If a power supply is smoking, unplug it.
Usually on a catastrophic failure, it usually kills the motherboard as well.
With a slow failure a voltmeter can be used.
Voltmeter should be set to 25 volts DC.
Testing on a 12 volt connector is the best.
Test a connector with a black ground and a yellow wire, which is 12 volts.
At 11 volts your motherboard won’t power up anymore.
A power supply should be tested under load.
A trick is using a paperclip connected to the green wire on the P1 connector which is the Power good wire. Use the paperclip as a jumper between the green wire and any black ground. This will start the power supply without connecting it to the motherboard.
Voltage testers made for power supplies are a good way also. Just plug it into any of the power supply connectors and it will signal a good or bad power supply.
Don’t forget to make sure everything is plugged in.
