CompTIA A+ 220-1201 (3.6 - Computer Power)

WARNING

• Always disconnect from the power source when working on a device

- Always. Seriously.

• Some devices store a charge in capacitors

- Know how to discharge before touching

• Never connect your body to any part

of an electrical system

- Do not connect yourself to the

ground wire of an electrical system

• Respect electricity

- It does not respect you

Computer power supply

• Computer uses DC voltage

- Most power sources provide AC voltage

• Convert 120 V AC or 240 V AC

- To 3.3 V DC, 5 V DC, and 12 V DC

• You'll know when this isn't working

- An important component

Amp and volt

• Ampere (amp, A) - The rate of electron flow

past a point in one second

- The diameter of the hose

• Voltage (volt, V)Electrical "pressure"

pushing the electrons

- How open the faucet is

Power

• Watt (W) - Measurement of real power use

- volts * amps = watts

- 120V * 0.5A = 60W

Current

Alternating current (AC)

- Direction of current constantly reverses

- Distributes electricity efficiently over long distances

- Frequency of this cycle is important

- US/Canada - 110 to 120 volts of AC (VAC), 60 hertz (Hz)

- Europe - 220-240 VAC, 50 Hz

• Direct current (DC)

- Current moves in one direction with a constant voltage

Dual-voltage input options

• Voltage varies by country

- US/Canada - 120 volts of AC (VAC), 60 hertz (Hz)

- Europe - 230 VAC, 50 Hz

• Manually switch between 120 V and 230 V

- Get your meter!

- Or use an auto voltage power supply

• Don't plug a 120 V power supply into

a 230 V power source!

Power supply output

• Different voltages

- For different components

• Positive and negative voltage

- Voltage is a difference in potential

- The electrical ground is a common reference point

- Depends on where you measure from

• At the front door of your house

- The second floor is +10 feet

- The basement is -10 feet

• +12 V

- PCIe adapters, hard drive motors, cooling fans,

most modern components

• +5 V

- Some motherboard components

- Many components are now using +3.3 V

• +3.3 V

- M.2 slots, RAM slots, motherboard logic circuits

• +5 VSB

- Standby voltage

• -12 V

- Integrated LAN

- Older serial ports

- Some PCI cards

• -5 V

- Available for ISA adapter cards

- Most cards didn't use it

- Today's motherboards don't have ISA slots

24-pin motherboard power

• Main motherboard power

- Provides +3.3 V, +/-5 V, and +/- 12 V

• 20 pin connector was the original ATX standard

- 24 pin was added for PCI Express power

• You can connect a 24-pin connector to a 20-pin motherboard

- Some cables are 20-pin + 4-pin

Redundant power supplies

• Two (or more) power supplies

- Internal to the server

• Each power supply can handle 100% of the load

- Would normally run at 50% of the load

• Hot-swappable

- Replace a faulty power supply without powering down

Power supply connectors

• Fixed connectors

- Connected to the power supply

- May have too many connectors

- May not have enough

• Modular

- Add cables as needed

- Fewer leftover wires,better airflow

- A bit more expensive

Sizing a power supply

• Power supplies are rated by watts

- Overall and by individual voltages

• Bigger isn't necessarily better

- More expensive

- Doesn't speed up your computer

• Physical size is relatively standard

- Older cases and systems may have proprietary sizes

• Calculate the watts required for all components

- CPU, storage devices, video adapter

- Many online calculators

• Video adapters are usually the largest power draw

- Many video card specifications list a

recommended power supply wattage

• 50% capacity is a good rule of thumb

- Power supply runs efficiently and

there's room to grow

Energy efficiency

• Converting AC to DC isn't perfect

- Some power is often lost

- Heat is generated

• Check the efficiency range

- Power supplies often range between 80% to 96%

- Can depend on voltage and redundant power

• More efficiency means more DC power

- And less heat; save money!

• There's an established certification program

- Pick the right efficiency for your requirements Overall

and by individual voltages