2.4 - Power

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

– 120 volts, 240 volts

Watt

Watt (W)

– How much energy is being consumed?

– Electrical load is measured in watts

• Easy to calculate volts * amps = watts

– 120 V * 0.5 A = 60 W

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

Device power supplies

• Devices commonly use DC voltage

– Most power sources provide AC voltage

• Convert 120 V AC or 240 V AC

– To DC voltages

• You’ll know when this isn’t working

– An important component

UPS

• Uninterruptible Power Supply

– Short-term backup power

– Blackouts, brownouts, surges

• Common UPS types

– Offline/Standby UPS

– Line-interactive UPS

– On-line/Double-conversion UPS

• Features

– Auto shutdown, battery capacity, outlets,

phone line suppression

Power distribution units (PDUs)

• Provide multiple power outlets

– Usually in a rack

• Often include monitoring and control

– Manage power capacity

– Enable or disable individual outlets