Power Supplies and Electrical Safety

Question

Answer

What should you always do before working inside a computer?

Disconnect from any power source

What can store power inside a computer even after disconnection?

Capacitors

What should be avoided regarding a building's electrical system?

Connecting yourself to it

What does a power supply unit (PSU) do?

Converts AC power from wall outlets into DC power for computer components

What type of power do wall outlets provide?

AC (alternating current)

What type of power do motherboards and components require?

DC (direct current)

What DC voltages does a PSU typically output?

3.3V

What AC voltage is used in the US/Canada?

120V

What AC voltage is used in Europe?

230V

What does Ampere measure?

The flow of electrons (current) past a point per second

What does Voltage measure?

Electrical "pressure"

What does Wattage measure?

Real power use

What is the formula for calculating Wattage?

Volts multiplied by Amps equals Watts

What characterizes AC (Alternating Current)?

It constantly reverses direction

What characterizes DC (Direct Current)?

It flows in one direction with constant voltage

What AC frequency is used in the US?

60Hz

What AC frequency is used in Europe?

50Hz

What can happen if the wrong voltage setting is used on a PSU?

Catastrophic failure

What does the +12V PSU output typically power?

PCIe adapters

What does the +5V PSU output typically power?

Motherboard components (older systems) and standby power

What does the +3.3V PSU output typically power?

RAM

What does the -12V PSU output typically support?

Legacy LAN connections and older PCI cards

Is the -5V PSU output commonly used today?

Rarely; found in older systems for legacy adapter cards

What is the primary power connector to the motherboard?

The 24-pin ATX connector

What voltages does the 24-pin ATX connector provide?

3.3V

Are 24-pin connectors backward-compatible with 20-pin systems?

Yes

What prevents incorrect insertion of the motherboard power connector?

It is keyed

What is a redundant PSU used for?

High availability in servers

What happens if one redundant PSU fails?

The other takes over

What does hot-swappable mean for a PSU?

It allows replacement without shutting down the system

What is a fully modular PSU?

One where all cables are detachable

What is a semi-modular PSU?

One where some cables are fixed and others are detachable

What does PSU wattage determine?

The PSU's capacity to support system components

How should you determine what PSU wattage to buy?

Sum component requirements and choose a PSU supporting about 50% more than peak load

What does PSU efficiency measure?

How well the PSU converts AC to DC

What certification system rates PSU efficiency?

80 PLUS (Bronze

What does higher PSU efficiency reduce?

Heat and operating costs