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By Root 1511 0

techs. Problems with power can create system instability, crashes, and data loss—all things most computer users would rather avoid! Good techs, therefore, know an awful lot about powering the PC, from understanding the basic principles of electricity to knowing the many variations of PC power supplies. Plus, you need to know how to recognize power problems and implement the proper solutions. Too many techs fall into the “just plug it in” camp and never learn how to deal with power, much to their clients’ unhappiness.

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EXAM TIP Some questions on the CompTIA A+ certification exams could refer to a power supply as a PSU, for power supply unit. A power supply also falls into the category of field replaceable unit (FRU), which refers to the typical parts a tech should carry, such as RAM and a hard drive.

Historical/Conceptual

Understanding Electricity

Electricity is simply a flow of negatively charged particles, called electrons, through matter. All matter enables the flow of electrons to some extent. This flow of electrons is very similar to the flow of water through pipes; so similar that the best way to learn about electricity is by comparing it to how water flows though pipes. So let’s talk about water for a moment.

Water comes from the ground, through wells, aquifers, rivers, and so forth. In a typical city, water comes to you through pipes from the water supply company that took it from the ground. What do you pay for when you pay your water bill each month? You pay for the water you use, certainly, but built into the price of the water you use is the surety that when you turn the spigot, water will flow at a more or less constant rate. The water sits in the pipes under pressure from the water company, waiting for you to turn the spigot.

Electricity works essentially the same way as water. Electric companies gather or generate electricity and then push it to your house under pressure through wires. Just like water, the electricity sits in the wires, waiting for you to plug something into the wall socket, at which time it’ll flow at a more or less constant rate. You plug a lamp into an electrical outlet and flip the switch, electricity flows, and you have light. You pay for reliability, electrical pressure, and electricity used.

The pressure of the electrons in the wire is called voltage and is measured in units called volts (V). The amount of electrons moving past a certain point on a wire is called the current or amperage, which is measured in units called amperes (amps or A). The amount of amps and volts needed so that a particular device will function is expressed as how much wattage (watts or W) that device needs. The correlation between the three is very simple math: V × A = W. You’ll learn more about wattage a little later in this chapter.

Wires of all sorts—whether copper, tin, gold, or platinum—have a slight resistance to the flow of electrons, just as water pipes have a slight amount of friction that resists the flow of water. Resistance to the flow of electrons is measured in ohms (Ω).

Pressure = voltage (V)

Volume flowing = amperes (A)

Work = wattage (W)

Resistance = ohms (Ω)

A particular thickness of wire only handles so much electricity at a time. If you push too much through, the wire will overheat and break, much as an overloaded water pipe will burst. To make sure you use the right wire for the right job, all electrical wires have an amperage rating, such as 20 amps. If you try to push 30 amps through a 20-amp wire, the wire will break and electrons will seek a way to return into the ground. Not a good thing, especially if the path back to the ground is through you!

Circuit breakers and ground wires provide the basic protection from accidental overflow. A circuit breaker is a heat-sensitive electrical switch rated at a certain amperage. If you push too much amperage through the circuit breaker, the wiring inside detects the increase in heat and automatically opens, stopping the flow of electricity before the wiring overheats and breaks. You reset the circuit breaker