Molex connector

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PC power supply with several connectors. From left to right: Molex Mini-fit Jr 20 and 4 pin, Molex KK, SATA connector, Molex 8981 and Molex mini-spox.

Molex connector is the vernacular term for a two-piece pin and socket interconnection, most frequently disk drive connectors. Pioneered by Molex Connector Company, the two-piece design became an early electronic standard. Molex developed and patented the first examples of this connector style in the late 1950s and early 1960s.[1][2] First used in home appliances, other industries soon began designing it into their products from automobiles to vending machines to mini-computers.

In such a connector, cylindrical spring-metal pins fit into cylindrical spring-metal sockets. The pins and sockets are held in a rectangular matrix in a nylon shell. The connector typically has two to 24 contacts and is polarized or keyed to ensure correct orientation. Pins and sockets can be arranged in any combination in a single housing, and each housing can be either male or female.

There are three typical pin sizes: 1.57 mm (0.062 in), 2.36 mm (0.093 in), and 2.13 mm (0.084 in). The 1.57 mm pin can carry 5 A of current, while the 2.36 mm can carry 8.5 A. Because the pins have a large contact surface area and fit tightly, these connectors are typically used for power.

This style of connector was first used as a computer disk drive connector in the late 1970s, initially on the Shugart floppy disk drive as well as Atari (1979) on its path to becoming a de facto standard. It is in this role that the vernacular term molex connector is most frequently used. AMP (now a division of Tyco International) developed the MATE-N-LOK 2.13 mm pin connector that is the same as the Molex 8981 power connector. This Molex and Amp connector configuration was the established standard for disk drive power connectors until the introduction of SATA drives.

Desktop PC use[edit]

Several connector types have become established for connecting power in desktop PCs, because of the simplicity, reliability, flexibility, and low cost of the Molex design. Certain Molex connectors are used for providing power to the motherboard, fans, hard disk drive, floppy disk drive, CD/DVD drive, video card, and others. Compatible connectors are available from many manufacturers, not just Molex and AMP.

Motherboard power connector (Molex Mini-fit Jr. 5566-20A or 5566-24A)[edit]

ATX Connector

In 20/24 pin configurations, the Mini-Fit Jr. connector may be used on ATX motherboards as the main power connector. 4, 6 and 8 pin configurations of the same style of connector are used for additional CPU power and graphics card power. This is changing as power, signal and speed requirements increase in sophistication and electronic requirements. More commonly, the Mini-Fit, Jr. can be found in consumer applications, such as white goods, requiring high density and high current.

These connectors are polarized so that they usually cannot be inserted incorrectly, and lock into position using a latch.

Standard pinout:

24-pin ATX12V 2.x power supply connector
(20-pin ATX connector omits the last four pins:
11, 12, 23 and 24)
Color Signal Pin Pin Signal Color
Orange +3.3 V 1 13 +3.3 V Orange
+3.3 V sense Brown
Orange +3.3 V 2 14 −12 V Blue
Black Ground 3 15 Ground Black
Red +5 V 4 16 Power on Green
Black Ground 5 17 Ground Black
Red +5 V 6 18 Ground Black
Black Ground 7 19 Ground Black
Grey Power good 8 20 Reserved N/C
Purple +5 V standby 9 21 +5 V Red
Yellow +12 V 10 22 +5 V Red
Yellow +12 V 11 23 +5 V Red
Orange +3.3 V 12 24 Ground Black
  • Pins 8, and 16 (shaded) are control signals, not power:
    • Power on is pulled up to +5 V by the PSU, and must be driven low to turn on the PSU.
    • Power good is low when other outputs have not yet reached, or are about to leave, correct voltages.
  • Pin 13 supplies +3.3 V power and also has a second thinner wire for remote sensing.[3]
  • Pin 20 (formerly −5 V, white wire) is absent in current power supplies; it was optional in ATX and ATX12V ver. 1.2, and deleted as of ver. 1.3.
  • The right-hand pins are numbered 11–20 in the 20-pin version.

Power good goes high to indicate that voltages are stabilised and ready for use. Power on is internally driven high, and shorting this pin to ground will turn on the power supply.

Disk drive connector (Molex 8981 Series Power Connector)[edit]

Molex 8981 Series
Molex female connector.jpg
Molex 8981 Power connector (female pins)
Type Electrical power connector
Designer Molex
Width 21 mm (female), 23 mm (male)
Height 6 mm (female), 8 mm (male)
Pins 4
Signal Yes
Max. voltage 12 V
Max. current 11 A/pin (30 °C rise)
Molex 8981 male connector pin out.png
Male Pins (Female Connector)
Pin Color Type
Pin 1 Yellow +12 V
Pin 2 Black Ground
Pin 3 Black Ground
Pin 4 Red +5 V
18 AWG wire is typically used.

The desktop computer hard-drive connector is pictured here. It has 4 conductors, with the standard pinout as follows:

Pin # Color Function
1   Yellow +12 V
2   Black Ground
3   Black Ground
4   Red +5 V

Sometimes, especially in older computers, the colors differ. The pins are 0.200 in (5.08 mm) apart (center to center). The connector housing has chamfered corners on one side to prevent the user from plugging it in incorrectly. The connector that provides power (e.g., on a power supply) has female pins and a male housing; the connector that receives power (e.g., on a peripheral) has male pins and a female housing.

The connector is standard on all 5.25 in floppy drives, PATA disk drives and non-SCA SCSI disk drives; however, newer SATA disk drives will employ a more advanced interconnection with 15 contacts. These new, advanced connection systems are being developed by Molex and other connector companies, often working together to develop interconnection standards. As SATA becomes more prevalent, Molex connectors can be found repurposed, through use of an adaptor, to serve as six-pin PCI-E power connectors to make up for a lack of such connectors on a power supply.

Lower power devices (e. g. 3.5 in floppy drives) use the smaller AMP 171822-4 connector instead.[4]

Despite its widespread adoption, the connector does have problems. It is difficult to remove because it is held in place by friction instead of a latch, and some poorly constructed connectors may have one or more pins detach from the connector during mating or demating. There is also a tendency for the loosely inserted pins on the male connector to skew out of alignment. The female sockets can spread, making the connection imperfect and subject to arcing. Standard practice is to check for any sign of blackening or browning on the white plastic shell, which would indicate the need to replace the arcing connector. In extreme cases (as in vintage pinball machines which often use this style of connector), the whole connector can melt due to the heat from arcing.

See also[edit]

References[edit]

  1. ^ Krehbiel, John H., "Wire Connector" US 3178673, issued April 1965
  2. ^ Krehbiel, John H., "Electrical Connector Having Resilient Accurately Bendable Locking Means", US 3409858, issued November 1968
  3. ^ "ATX Specification Version 2.1". 
  4. ^ Tyco Electronics EI series

External links[edit]

  1. ^ Krehbiel, John H., "Wire Connector" US 3178673, issued April 1965
  2. ^ Krehbiel, John H., "Electrical Connector Having Resilient Accurately Bendable Locking Means", US 3409858, issued November 1968
  3. ^ "ATX Specification Version 2.1". 
  4. ^ Tyco Electronics EI series