Powering the Portable

Powering the Portable

Adaptable, lightweight, and long-life power sources play a large part in the usability of a portable PC system. Essentially, three general types of power sources, described as follows, are available for portable PCs — each designed to provide it with power either in the office or on the road:

  • AC/DC adapter: This adapter works much like the power supply in a desktop computer to convert the wall socket AC power into DC power. AC adapters are also used to recharge the portable PC’s battery. You are probably familiar with this type of device because it’s used on a wide range of electronic products — including games, calculators, and external computer peripherals.

  • Battery: The battery is an integral part of any portable PC because without it, the PC would not be as portable. Instead, users would need very long extension cords and would have to depend on having an AC outlet everywhere they go.

  • Docking station: In addition to the power that it provides the PC, the docking station enables the PC to connect to full-sized expansion cards and additional ports, and allows the portable PC to connect to and drive the peripherals (such as monitors and printers) that are usually connected to a desktop computer. A port replicator is typically a smaller version of the docking station that provides only additional I/O ports.

Portable PC power systems

 Remember  The power supply of a portable PC is focused on power conservation rather than power regulation; the latter is the aim of a nonportable PC power supply. A portable PC runs on DC power like other PCs, but the portable runs straight from a battery. This means that the portable PC supply does not convert AC to DC to power the motherboard, processor, video display, and peripheral devices. AC power recharges the battery, but it does not power the PC.

Managing portable PC power

Virtually all portable PCs now have some kind of a power-management system, most often as a software battery monitor. This system tracks the reserve power of the battery and reports the battery’s strength as a percentage. A report of 70 percent means that you’ve used only 30 percent of the battery’s capacity. Many power-management systems also check whether the PC is in use; if it’s not, the power-management system suspends the PC to conserve the battery’s power. Conserving a battery and extending its life is a much better — and less expensive — choice than replacing the battery.


Power management is a major concern for all portable computing device owners. Nearly all notebook PC and portable device owners look for and take advantage of anything that will help save battery power.

Nearly all notebook PCs are configured with either the Advanced Configuration and Power Interface (ACPI) or the Advanced Power Management (APM) technologies. ACPI is the newest of these technologies and APM is a legacy technology.

ACPI is configured in the BIOS and APM is implemented through an application programming interface (API). ACPI is a collection of BIOS code routines, where APM is an operating system directed configuration and power management technology for portable PCs, as well as desktop and server computers.

The benefit of ACPI is that it lets the PC control the power supply to peripheral devices, such as the CD-ROM, printer, and other external devices. In a turn about is fair play twist, the peripherals also have the ability to use ACPI to power on the PC. For example, if you insert a CD-ROM into a CD-ROM drive, the PC automatically boots up from a power off state.

Portable PC battery types

Expect a question about portable PC battery characteristics on the A+ Hardware Technology exam.

Portable PCs use the following types of batteries:

  • Alkaline: These are the same batteries that are common for your calculator, TV remote control, and portable tape player.

    This type of battery is used in some palmtop computers.

  • Nickel Cadmium (NiCad): This is the most popular and durable type of rechargeable battery. This battery is also the heaviest, yet least expensive, of the portable PC battery types. It is also quick to charge and has a reasonable life of around 700 charge-and-discharge cycles.

  • Nickel-Metal Hydride (NiMH): Unlike NiCad batteries, these batteries are environmentally friendly because they don’t contain heavy metals that can be toxic. They also store up to 30 percent more power than NiCad batteries of the same weight.

    Some of the disadvantages of NiMH batteries are that they have a shorter life (around 400 charge-and-discharge cycles) and cost about 30 percent more than NiCad batteries.

  • Lithium Ion (Li-Ion or LiON): Very lightweight with a long battery life, this type of battery is made with one of the lightest available metals (lithium). LiON batteries hold about twice the power of a NiCad battery in about half the weight. Compared to a NiMH battery of equal weight, a LiON delivers twice the run time from each charge. The LiON battery type has about the same life cycle as NiCad and NiMH batteries. LiONs are not generally available for all models; they’re usually more expensive than other battery types.

    A LiON battery is probably the best choice for a portable PC, but it can be more expensive than the other choices.

Running off fuel cells

Fuel cells are a new objective of the A+ Hardware Technology exam. They are a power source for portable PC systems. However, I doubt that you will see an exam question about fuel cells.

Fuel cells have been talked about for some time, but always in the future tense. However, Toshiba now has a prototype direct methanol fuel cell (DMFC) battery for its portable PCs. The primary advantages offered by fuel cells are that they have a longer life, which means they can run the portable system longer, and they don’t need recharging, which could be a real cost savings in the long run. The Toshiba DMFC (Direct Methanol Fuel Cell) battery offers a small form factor with an average output of 12 watts and a maximum output of 20 watts, for up to 5 hours. The DMFC battery fits in the same space and uses the same connectors as the lithium-ion battery.

A fuel cell battery produces electricity like an ordinary battery — using electrochemical reactions. The difference between the two is in the fuel cell’s ability to produce electricity as long as it has a fuel source (such as methanol, aluminum, hydrogen, and other substances), while an ordinary carbon battery must be recharged periodically. Fuel cell batteries don’t store electricity and can’t run down like an ordinary battery. Fuel cells convert fuel into electricity; ordinary carbon batteries store electricity that’s provided from an external source.

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