Chp.5 Power

Chp.5 Power

1. Understanding power

   • Voltage
     • potential energy; referred to as pressure
     • measured in volts (V)
   • wattage or electrical power
     • rate of electricity in a circuit
     • measured in watts (W)
   • Amperage or electric current
     • movement of electrical charge
     • measured in amperes or amps (A)
   • Impedance
     • amount of resistance to electricity
     • measured in ohms
   • Alternating current (AC)
     • electron flow alternates
       • 120 V AC (outlets)
   • Direct current (DC)
     • electrons flow one way
       • 5 volts DC (Internal power in PCs)

2. Power Devices

   • Surges
     • unexpected increase in the amount of voltage provided
   • Spikes
     • a surge with a small or large increase of voltage
     • short transient in voltage that can be due to
       • short circuit
       • tripped circuit breaker
       • power outage
       • lightning strike
   • Sags
     • unexpected decrease in the amount of voltage provided
       • limited in time and in the decrease of voltage
   • Brownouts
     • during a sag when voltages reduce further, a brownout could ensue
       • voltage drops to such an extent that it typically causes the lights to dim and cause computers to shut off

3. Power Strips

   • a group of sockets, usually in-line, with a cable to plug in AC outlet
   • has a master on/off switch and usually has a 15-amp circuit breaker to prevent overloading
     • occurs because the power strip tries to pull too much power (amps) from wall outlet, or when too much current is supplied to the power strip

4. Surge Protectors

   • a power strip that also incorporates a metal-oxide varistor (MOV)
     • protects against surges and spikes
     • every time a surge happens, part of the varistor is burned out
       • the higher the joule rating the longer the varistor should last
   • rated in joules

5. Uninterruptible Power Supplies

   • takes the functionality of a surge protector and combines that with a battery backup
     • typically keeps system running for 5 to 30 minutes
   • also acts as line conditioners, protecting from over-and under-voltage
   • output rated in volts-amps(VA)

6. Troubleshooting

   • to troubleshoot power supplies
     • multimeter, power supply tester
     • eyes,and ears
   • issues encountered with power supplies
     • fan failure
       • old PSU, clogged with dirt, cheap fan design (no ball bearings)
         • replace power supply
       • can produce loud noise
     • fuse failure
       • can be cause by overload and PSU malfunctioning
         • replace power supply
     • quick death
       • electrical spike to hardware malfunction
         • Test AC outlet with receptacle tester
           • verify surge protectors and/ or UPS
     • slow death
       • can cause intermittent issues, failure of hard drives, and other devices
         • check power cord and swap PSU for known good one
   • heating and cooling
     • system overheating can be caused by
       • PSU fan failure, Aux. case fan failure, inadequate amount of fans, and missing or open slot covers
         • also case isn't tightly closed
           • location of computer