FAQ: Power Pinouts and Wiring

Here is a reference for the pinouts for the various power plugs in a PC. There are numerous sources so I found the ones with the best pics and diagrams. I AM NOT RESPONSIBLE FOR ANY DAMAGES DONE USING THE FOLLOW INFORMATION.

General Wiring
These are the standard wire colors but not all manufacturers follow it. The pinouts diagrams are more reliable.
Black = Ground
Orange = +3.3v
Red = +5v
Yellow = +12v
White = -5v
Blue = -12v



Wiring VDrop Calculator
Longer and thinner wires increases Vdrop. Calculator is at the bottom of the page. Most PSUs use 18ga wires and occasionally 20ga. If you notice, these wires are rated to handle more current than what we normally provide. The reason is that as you increase the current through the wire, the more voltage-drop will be experienced.
http://www.powerstream.com/Wire_Size.htm



Motherboard
24-pin ATX, main plug on motherboards (short pin 16 to any GND to turn the PSU on)
http://pinouts.ru/Power/atx_v2_pinout.shtml

20-pin ATX, main plug on older motherboards (short pin 14 to any GND to turn the PSU on)
http://pinouts.ru/Power/atxpower_pinout.shtml

4-pin AUX, used on motherboards to power CPU
http://pinouts.ru/Power/atx12v_pinout.shtml

8-pin EPS, desktop motherboards can use just 4-pin AUX
http://www.playtool.com/pages/psucon...tors.html#eps8



Peripheral
4-pin floppy
http://pinouts.ru/Power/SmallPower_pinout.shtml

4-pin "Molex" peripheral
http://www.technick.net/public/code/...mth_power_5_25

SATA (pins 1,2,3 are not needed for desktop PCs. The 3.3v are used for delayed startup in servers)
http://pinouts.ru/Power/sata-power_pinout.shtml

3-pin Fan, sensor is optional.
http://www.interfacebus.com/ATX_Moth...or_Pinout.html

4-pin PWM fan, sensor and control are optional
http://pavouk.org/hw/fan/en_fan4wire.html




Motherboard Slots
PCI can each provide 25w at 3.3v, 25w at 5v, and 6w at 12v. However, total power is shared among all PCI slots. A motherboard maybe able only to provide a combined 100-150w to all the PCI slots.

PCI-X provides up to 25w, [more to come]

AGP provides up to 25w at 12v, [more to come]

PCI Express provides up to 75w at 12v

PCI Express 2.0 provides up to 150w (200w+ is possible) at 12v

USB, do not exceed 2.5w at 5v
http://pinouts.ws/usb-pinout.html

Firewire [IEEE1394], do not exceed 15w varying 12-25v
http://pinouts.ru/Slots/ieee1394_pinout.shtml



Video Card
6-pin PCIe, delivers 75w: three +12v, three GND

8-pin PCIe, delivers 150w: three +12v, five GND (not electrically compatible with the CPU's EPS plugs!)
Edited by DuckieHo - 7/24/09 at 6:10am

+12v = +12v
GND = GND

In theory, the 8-pin PCIe plug can be replaced with just one +12v and one GND plug. However, the only reason that they split the plug up is to reduce wire resistence. You get much greater Vdrop and heat if you push 100w on a single long 18ga wire than 4 long 18ga wires. If your apdapter length is short and you are using thick wires, there should be no issues.

Good idea... I'll add which plug is providing power later.

Probably that the vDrop is consider acceptable...

Vdrop of 75w with three 18ga copper wires over 2ft = 0.055v (a .46% drop on 12v)
Vdrop of 150w with four 18ga copper wires over 2ft = 0.082v (a .68% drop on 12v)