Datasheet

Working with Power Supplies

As a general rule, you should have a large enough power supply for all the

slots in the computer with the most likely devices that will be installed. In

other words, you should calculate the power-supply capacity from what is

possible and not just what is currently on the motherboard.

TABLE 1.6 Estimating Power Consumption

Component Watts Consumed, for Estimating Purposes

Motherboard 20–30 watts

CPU 30–70 watts (faster CPU, more watts)

AGP video card 20–50 watts

PCI circuit boards 5 watts each

ISA circuit boards 10 watts each

Floppy drive 5 watts

CD drive 10–25 watts

RAM 8 watts per 128MB

IDE hard drive 5–15 watts

SCSI hard drive 10–40 watts

Power-Supply Problems

Power-supply problems can include randomly frying parts if there is a short. The fan failing

will cause annoying sounds and the system will overheat. One key reason the fan can fail is

if it is clogged with dust and debris.

Be aware that different cases have different types of on/off switches. The process of

replacing a power supply is a lot easier if you purchase a replacement with the same mecha-

nism. Even so, remember to document exactly how the power supply was connected to the

on/off switch before you remove it. Be careful, as well, to set the voltage selector switch on

the power supply to correspond to your voltage. Most power supplies have the ability to

accept input of either 110 or 220 volts. Some expensive power supplies can autosense and

need not be set manually, but most do and you want to set the switch to the correct voltage

setting or you could cause damage.

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