Power Supplies - Upgrading and Repairing PCs - page 896

overloads is the reason the extra pins were added in the first place.
Some motherboards sold from 2004 through 2010 that use a 24-pin main power connector also have
an additional peripheral (that is, disk drive) power connector onboard designed to provide the extra
power that would be missing if you connected a 20-pin main power connector from your power
supply. The documentation for these motherboards refers to this as an alternate or auxiliary power
connector . Some boards included both standard and SATA style drive connectors to supply this extra
power.
If you plug a 24-pin main power connector into the 24-pin socket on the motherboard, the alternate or
auxiliary power connection is probably unnecessary. However, if you plug a 20-pin main power
connector into the 24-pin main power socket on the motherboard, and that board has one of these
alternate or auxiliary power connectors on board, then you should probably use it. In that case simply
select a spare peripheral (disk drive) power connector from the power supply and plug it into the
alternate or auxiliary power connector. Most power supplies have several extra peripheral or SATA
power connectors for supporting additional drives. Using a 20-pin main and the alternate or auxiliary
power connector satisfies the power requirements for the motherboard and any PCI Express x16
video cards drawing up to 75 watts.
As a side note, be careful when plugging in the mismatched connectors so that they are offset
properly. The main, +12V, and PCI Express graphics connectors are Molex Mini-Fit Jr.-type
connectors that are keyed by virtue of a series of differently shaped plastic protrusions used around
the terminals, which fit similarly shaped holes in the mating connectors. This keying is designed to
prevent backward or improper off-center insertion, but I have found two problems with the keying
that should be noted. One is that some alternate low-quality connector brands are built to looser
tolerances than the original high-quality Molex versions, and the sloppier fit of the low-quality
versions sometimes allows improper insertion. The other problem is that, with sufficient force, the
keying on even the high-quality versions can be overcome. Because plugging a 20-pin connector into
a 24-pin socket—or a 24-pin connector into a 20-pin socket—is designed to work even though they
don't fully match up, you need to make sure you have the offsets correct or you risk damaging the
board when you power it up.
Dell Proprietary (Nonstandard) ATX Design
Most of these systems are no longer in use, but if you upgrade or repair any Dell desktop systems
made between 1996 and 2000, you should be aware that they used a nonstandard design, and
upgrading either the motherboard or power supply can result in the destruction of the motherboard,
power supply, or both! For more information about this, please see the 20 th or earlier editions of
Upgrading and Repairing PCs .
Additional Power Connectors
Besides the motherboard power connectors, all power supplies include a variety of additional power
connectors, mainly used for internally mounted drives but usable by other components, such as
graphics cards. Most of these connectors are industry-standard types required by the various power
supply form factor specifications. This section discusses the various types of additional device
power connectors you're likely to find in your PC.
Peripheral Power Connectors