Coaxial power connector

Coaxial power connector
Most common coaxial power connector, male and female, 5.5 x 2.5 mm
Common DC power connectors

A coaxial power connector is a miniature power connector used for attaching extra-low voltage devices such as consumer electronics to external electricity. Also known as barrel connectors, concentric barrel connectors or tip connectors, these small cylindrical connectors come in an enormous variety of sizes.

The primary use of these plugs is as a DC connector (or sometimes AC) on the cable that comes from an external power supply. The matching jack or socket is then mounted in the equipment to be powered. Some of these jacks contain a normally closed switch; the switch can disconnect internal batteries whenever the external power supply is connected, to avoid the risk of battery leakage or explosion posed by incorrect recharging of the batteries.


Connector construction and terminology

Some power plugs are merely miniaturized phone plugs (jack plugs in the UK) which have been pressed into service as power connectors. The two connectors on the left of the picture above are subminiature and miniature phone plugs respectively, the subminiature size being 3/32 inch and the miniature being 1/8 inch in diameter. The original application of these connectors was for audio microphones and headsets. Miniaturized phone plugs are typically 3/32 inch, 1/8 inch, 2.5 mm, or 3.5 mm in diameter, whereas the original full-sized telephone plug was 1/4 inch in diameter. Phone plug connectors were not originally designed to carry power, and there is a possibility of momentary or continuous short circuiting the power supply when mating the connector.

By contrast, coaxial power connectors were specifically designed to carry electrical power, and usually have features intended to make connections safer and more reliable. Typically, the outer body of the plug is one metallic contact, most often but not always connected to the negative side of the power supply. Coaxial power connectors generally have a cylindrical hollow insulated tip constructed to accept insertion of a pin (note that exceptions are described later). A pin mounted in the corresponding socket connects with this second contact, which is an internal metallic surface lining the inside of the tip of the plug.

The outer plug contact is usually called the barrel or sleeve, and the inner contact is called the tip (by analogy to the same terms used for phone plugs), although in the case of most coaxial power connectors the very end of the tip itself is a non-conductive ring.

Technically, most coaxial power plugs are considered to be of "female" gender, and most coaxial power jacks are considered to be "male". For a more detailed discussion of this naming convention, see the article on gender of connectors and fasteners. As a notable exception, some special-purpose coaxial power connectors typically used for higher power levels are male gender, e.g. the larger size EIAJ plugs.

In a typical coaxial power configuration, the mating jacks or sockets have a somewhat oversized circular opening with a pin in the center. There is typically a single spring-loaded contact at the side of the opening, so some variation in mating plug barrel diameters can be accommodated. If the central pin of the jack is too large for the opening in the plug tip, it is not possible to make the connection. The pin should be designed to be just slightly smaller than the hole, to make a reliable connection. If the pin is substantially smaller, the connection may appear to work but may also be somewhat loose and unreliable.

Most coaxial power connectors are not sealed against entry of water or dust, but at least one manufacturer (Switchcraft) has announced a series of water-resistant coaxial power plugs and jacks.[1]

Many different sizes

There are many different sizes of coaxial power connectors (see table at end of this article.)

Contact ratings vary from unspecified (and probably less than 1 A in practice) up to 5 A, with 2 A typical. Voltage is again often unspecified, up to 48 V with 12 V typical. The smaller types usually have lower ratings, both for current and voltage.

It is quite possible that new sizes will continue to appear and disappear. The most likely reason for a new size is that a particular manufacturer wishes to discourage use of third-party power supplies, either for technical reasons or to promote use of their own products, or both.

Furthermore, sometimes there is no rhyme or reason to the choice of which connector is used in an application. For example, one manufacturer might use a particular size connector for its 12 V 1 A product; a second manufacturer might use a different connector for its 12 V 1 A product. Although the power supplies may be otherwise identical, they are not interchangeable because the connectors are different.

A more disastrous situation occurs when different manufacturers use the identical connectors for very different power supply voltages and currents. Use of the wrong power supply may cause severe equipment damage, or even fire.

Common sizes and interchangeability

Some common DC power connectors

The most common plugs are 5.5 mm in outside diameter (OD) and 9.5 mm in length. Two inside diameters (ID) are common in the plugs for this size, 2.1 mm and 2.5 mm, and ideally the pin in the jack should match. Generic plugs are often named after the inside diameter, so these types will be seen described as 2.1 mm DC plugs and 2.5 mm DC plugs respectively. These two sizes are easy to visually confuse, unless compared side by side. Slightly smaller 5.0 mm OD plugs are sometimes used in both 2.1 mm and 2.5 mm sizes, and are also frequently misidentified. Plug connector barrels for all of these sizes are typically 8 mm to 14 mm in length, with 9.5 mm most common.

After the two common 5.5 mm OD plugs, the next most common size is 3.5 mm OD with a 1.3 mm ID, commonly 9.5 mm in length but both longer and shorter versions also exist. These 3.5 mm OD plugs are normally used for lower voltages and currents.

There are also 6.5 mm OD plugs with a 3 mm ID, 3.8 mm OD plugs with either a 1.35 mm or a 1.05 mm ID, 3.5 mm plugs with a 1.3 mm ID, and many less common sizes.

Use of a plug designed for a larger pin, for example a 2.5 mm plug with a 2.1 mm pin jack, may work adequately depending on the design of the jack, but often the result is an unreliable contact or occasionally no contact at all. A pin that is too large for the plug will not allow insertion of the plug at all. Similarly, a larger plug barrel (OD) may not fit at all; a smaller one may fit but may not make a reliable contact. Length is less critical than the diameters but is sometimes a consideration; in general a longer plug is no great problem but a shorter one may fail to contact the pin reliably or at all.

It is possible to obtain connector size adapters with a DC coaxial female connector on one end, and a different-sized DC coaxial male connector on the other end.[2]

Locking and retention features

A ring-shaped locking detent or high-retention feature, present on the barrel of some DC coaxial connectors, is a feature intended to prevent accidental disconnection. Its presence or absence can cause confusion when distinguishing very similar sizes and variants. Some of the sizes listed appear to always include a high-retention feature, while others include it only in designs from certain manufacturers. Typically, this feature is a conical cut-back section of the tip, just behind the insulator that separates the inner from outer contact surfaces. In particular, the EIAJ (JEITA RC-5320A) standard connectors appear to specify a high-retention design.

The preceding very common feature must not be confused with the much-less-prevalent lock-ring DC coaxial connector which uses a captive threaded ring or collar to secure the connection between the plug and jack. Manufacturers known to offer this variant on at least some connectors include CUI, Kobiconn, Philmore, and Switchcraft. Note that this design requires that the lock-ring threading size be compatible with sufficiently protruding threads on a mating panel jack, and that some manufacturers (notably Switchcraft) have used a mix of metric and inch dimensioning. The lock-ring design, when fully engaged, offers strong resistance to unplugging; it is so secure that if the power cord is accidentally pulled forcefully, severe mechanical damage to equipment is likely.

An alternate design, the even rarer lock-tab DC coaxial connector (also called bayonet lock) offers a compromise that resists unplugging, but which will disengage when pulled hard enough. This connector uses small metal tab protrusions on the connector barrel to lock the plug in place, requiring a special push-and-rotate motion to engage the locks. This is a mechanical way to provide a "safe breakaway" feature somewhat like the magnetic latch used in the Apple Inc. proprietary MagSafe design. Kobiconn and Lumberg have offered some lock-tab variants, and there may be other manufacturers as well.

To insure that locking connectors operate properly, it is important to specify and to test this feature. It is likely that mating connectors from a single manufacturer will interlock correctly, but even in this case, compatibility should be verified.

A completely different series of locking connectors is the snap and lock DC connector, which is not a coaxial power connector, and is covered in a separate article on DC connectors. These multi-pin DC power connectors typically have 3 or 4 or more pins, and somewhat resemble mini-DIN connectors, except that the connector pins are thicker, to carry more current.


Close-up of a yellow-tipped EIAJ connector. Note 2 round adapter pins on the opposite end.

In an ideal world, specifying a voltage and a current for a power supply would also determine the connector, and it would be physically impossible to connect damaging voltages to a powered device. The world is far from that situation, but a few tentative steps have been taken in that direction.

At least two different national standards have been established, by EIAJ in Japan and DIN in Germany. In addition, several conventions have been adopted by specific manufacturers, notably by Sony, to indicate voltage by plug size.

Over time, there has been a trend to de facto standardize with negative DC voltage on the barrel (or sleeve) of a coaxial power connector. For example, Sony reversed its corporate standard during the 1990s, and adopted a barrel negative convention. One advantage of the barrel negative setup is its lower risk of short circuiting in automotive applications, since grounding the negative terminal of car batteries to the chassis has become an almost-universal standard. But barrel positive polarity is still occasionally seen, along with the continued usage of coaxial power connectors for low voltage AC power as well.

Some generic power supplies allow the polarity to be reversed by use of a switch, or by an unpolarized 2-pin plug and socket arrangement. There appear to be at least two not-quite-compatible standards in existence for these 2-pin connectors, and official specifications are hard to find.

One "standard" used by RadioShack for its Adaptaplug brand features pins measuring 1.5 mm in diameter, 6 mm long, spaced 4 mm apart (center-to-center). Another "standard" features asymmetrical pins measuring 1.3 mm and 1.9 mm in diameter, 5 mm long, spaced 4.4 mm apart (center-to-center). There are probably other "standards" in use as well; it is not known how many different 2-pin connector systems of this type exist.

RadioShack, Kobiconn, and Philmore sell these types of 2-pin adapter connectors, and they also sell DC power cables with mating 2-pin female connectors.

EIAJ power connectors

Five plug and matching socket or jack designs are defined by the EIAJ standard RC-5320A (also called JEITA RC-5320A). Each of these plugs is used with a specified voltage range. Most manufacturers use a yellow insulating material to distinguish these plugs from other similar-looking DC plugs.

  • EIAJ-01 for 0–3.15 V
  • EIAJ-02 for 3.15–6.3 V
  • EIAJ-03 for 6.3–10.5 V
  • EIAJ-04 for 10.5–13.5 V (also called JSBP 4)
  • EIAJ-05 for 13.5–18 V (also called JSBP 5)

Unlike most DC plugs, the larger two EIAJ sizes have an internal male pin in the plug. The smaller three sizes do not, and are similar to the generic plugs in structure. The plug length is 9.5 mm in all cases, and current rating is 2 A.

There are two other, less common, connectors defined by EIAJ; RC-5321 and RC-5322. The latter is designed for both 12 V and 24 V automotive applications.

DIN 45323 power connectors

The German national standards organization DIN (Deutsches Institut für Normung — German Institute for Standardization) has issued DIN 45323, which apparently defines two DC power plug sizes. At least one of these sizes has a maximum rating of 34 V and 3 A. The information here is inferred from catalog references,[3] as the German standard has not been translated into English as of yet.

  • 5.00 mm OD, 2.00 mm ID, 14 mm long?
  • 6.00 mm OD, 1.98 mm ID

Guidelines for power connector selection

With more than 40 different designs of coaxial power connectors in existence which are used to power electronic products, the lack of a clear starting point for selecting one has helped lead to the wide inconsistencies among various power plugs and devices. Here are some guidelines that can be drawn from the few power connector designs that have clear voltage specifications associated with them.

  • 1.5 V devices
    • EIAJ-01
  • 3.0 V devices
    • EIAJ-01
  • 4.5 V devices
    • EIAJ-02
    • EIAJ RC-5321
  • 6.0 V devices
    • EIAJ-02
    • EIAJ RC-5321
  • 7.5 V devices
    • EIAJ-03
  • 9.0 V devices
    • EIAJ-03
  • 10.5 V devices
    • EIAJ-03
  • 12.0 V devices, including automotive electrical systems
    • EIAJ-04
    • EIAJ RC-5322 for automotive use
    • ARINC 628/EmPower for automotive or airplane use
  • 13.5 V devices
    • EIAJ-04
    • EIAJ RC-5322 for automotive use
    • ARINC 628/EmPower for automotive or airplane use
  • 15.0 V devices
    • EIAJ-05
    • ARINC 628/EmPower for automotive or airplane use
  • 16.5 V devices
    • EIAJ-05
  • 18.0 V devices
    • EIAJ-05

Note that the special ARINC 628/EmPower connector (which strictly speaking is not a coaxial power connector) is used aboard commercial airlines to provide electrical power to passenger's electronic equipment.

Comprehensive listing of DC coaxial connectors

This list attempts to show all known sizes, and is annotated with some manufacturers producing selected types (based on those found in the Mouser, Digi-Key, Newark, Allied, EVG and other online catalogs), since each manufacturer makes its own unique subset of the known types. Note that the example part numbers given may have different connector barrel (sleeve) lengths, and are not necessarily exact equivalents. There are many more design variants than can be listed in this table, so only a small sampling of part numbers is given.

By convention, connector size is often listed in the format A.AA x B.BB x C.CC, where A.AA is the Outside Diameter (OD), B.BB is the Inside Diameter (ID), and C.CC is the Length of the connector barrel, all measured in millimeters (mm). However, some manufacturers arbitrarily reverse the A and B dimensions, sometimes within the same page of their catalog. It appears that the most common barrel length is 9.50 mm, but shorter and longer connector barrels are in use.

A further distinction is made between the Inside Diameter (ID) and the Center Pin Diameter (CPD) for certain larger coaxial power plugs equipped with a male pin, which are often used for higher power applications such as portable computers. Some equipment manufacturers (e.g. Apple Computer, before it switched to its even more proprietary MagSafe connector) use designs that are incompatible in subtle aspects. Connectors for these applications must be specified carefully to avoid severe equipment damage or even fire, due to the higher power carried by these designs.

An alternate connector size convention uses the format W.WW x X.XX x Y.YY x Z.ZZ, where the dimensions are arranged in an ascending size order. In this labeling scheme, W.WW is the Center Pin Diameter (CPD) of an optional male center pin, X.XX is the Inside Diameter (ID), Y.YY is the Outside Diameter (OD), and Z.ZZ is the Length of the connector barrel, all measured in millimeters (mm).

It is apparent that there are many partially overlapping standards in this product category. There are ad hoc minor variations in specs, and illogical inconsistencies in part numbers, even among the offerings of a single manufacturer. Confusion and irregularity are widespread, requiring a close reading of the specifications or testing of physical prototypes, or both, to insure connector compatibility. This table is provided primarily for convenience in comparing information from a wide range of possible sources, and may contain errors; it is recommended to double-check before relying upon the specs listed.

There are a number of sizes listed below that appear to be quite similar, and while the tolerances of these connectors are typically indicated as ±0.05 or ±0.03 mm by the manufacturers, there is still ambiguity as to whether two sizes differing by only 0.05 mm (or where the specification is only given to the nearest 0.10 mm) warrants listing them separately here. Also, there are minor tolerancing and measuring variations and discrepancies in the dimensions given; further work should be done to determine the original specifications for size, and then to list the similar sizes that are intended to be compatible.

OD (mm) ID (mm) CPD (mm) Barrel length (mm) Adaptaplug Standard Volts Plug part numbers Jack part numbers Notes
2.35 0.70   9.5 A EIAJ-01 0–3.15 V Kobiconn 3218-EX
Lumberg 1636 01
Kobiconn 0307-EX (inline)  
2.40 0.70           Egston 212   possibly a rounded-off representation of EIAJ-01
2.40 0.80           Egston 213    
3.00 1.00                
3.00 1.10     G     CUI Inc. PP-019
Egston 214
3.20 0.90           CUI Inc. PP-017    
3.40 1.30     H     Kobiconn 3210-E Kobiconn 0309-EX (inline)  
3.40 1.35           Egston 218 Medical, 220    
3.40 1.40           Lumberg NES/J 135    
3.50 1.10           CUI Inc. PP3–002C
Philmore 202
3.50 1.30           Egston 238
Philmore 204,2049
Kobiconn 0308-EX (inline)
Philmore 256 (inline)
3.50 1.35           CUI Inc. P7
CUI Inc. PP3–002D
Egston 215
Kobiconn PA35135-E
3.60 1.15           Egston 216    
3.80 1.10     I     CUI Inc. P9 but with 1.05 mm ID    
3.80 1.30           Egston 217    
3.80 1.35           CUI Inc. P8    
4.00 1.70   9.5 B EIAJ-02 3.15–6.3 V Kobiconn 3219-EX
Lumberg 1636 02
Kobiconn 0311-EX (inline)  
4.75 1.70   9.5 C EIAJ-03 6.3–10.5 V Kobiconn 3220-EX
Lumberg 1636 03
Kobiconn 0310-EX (inline)  
4.75 ?.??   2.5 protruding C EIAJ RC-5321        
5.00 1.50     J          
5.00 2.00       DIN 45323?   Egston 206,207,219    
5.00 2.10     K     CUI Inc. P3    
5.00 2.50     L     CUI Inc. P4    
5.50 1.50     S          
5.50 2.10     M     CUI Inc. P5
CUI Inc. PP3–002A
Kobiconn 3217-EX
Philmore 210, 210L, 2109
Switchcraft S-760, S-765
CUI Inc. PR-002A (inline)
Kobiconn 0302 (inline)
Philmore 257 (inline)
Switchcraft 722A (panel) 
2.1 mm center pin
5.50 2.10           CUI Inc. P10
Kobiconn 7391
Philmore 2560
Switchcraft S760K
  2.1 mm center pin, lock-ring
5.50 2.10           Kobiconn 0721-EX Kobiconn 1000-EX (panel) 2.1 mm center pin, lock-tab
5.50 2.50     N     CUI Inc. P6
CUI Inc. PP3–002B
Egston 222
Kobiconn 0702-EX
Philmore 250, 250L, 2509
Switchcraft 760, 765
CUI Inc. PR-002B (inline)
Kobiconn 0303 (inline)
Philmore 258 (inline)
Switchcraft 712A (panel) 
2.5 mm center pin
5.50 2.50           CUI Inc. P11
Kobiconn 7395
Philmore 2560
Switchcraft 760K
  2.5 mm center pin, lock-ring
5.50 2.50           Kobiconn 0725-EX Kobiconn 1100-EX (panel) 2.5 mm center pin, lock-tab
5.50 2.80     O          
5.50 3.30 1.00 9.5 D EIAJ-04, JSBP4 10.5–13.5 V Lumberg 1636 04   Microsoft Xbox 360 HD DVD drive
5.50 3.80 1.80   P          
6.00 1.98       DIN 45323   Lumberg 1632 01    
6.30 3.00     Q          
6.50 ?.??       EIAJ RC-5322        
6.50 3.00                
6.50 3.10 1.00         Philmore 285    
6.50 3.40 1.40 9.0     18 VDC @5A Kobiconn 6014-E    used often for laptop computers 
6.50 4.10/3.10 1.00   U         same as Philmore 285?
6.50 4.30 1.40   T EIAJ-05, JSBP5 13.5–18.0 V Lumberg 1636 05   OD is of ring at tip
6.90 4.20 0.70   R          
7.00 ?? 1.00         Philmore 48-412    

RadioShack Adaptaplug conversion matrix

Adapter plugs that convert from the earlier-described two-pin non-polarized connector to various DC power plugs are widely sold by RadioShack. They have assigned a single-letter code to each "Adaptaplug", but have not provided any other official designation, nor their complete specifications and tolerances on barrel and pin dimensions. Note that the diameters listed on the RadioShack website are only specified to the nearest 0.1 mm, and sometimes differ slightly from the official EIAJ RC-5320A standards, when applicable. This list may include some discontinued parts, which are nevertheless retained for completeness.

Adaptaplug Outside












Radio Shack

part number

A 2.3 mm 0.7 mm EIAJ-01 up to 3.15 V Yellow 3807936
B 4.0 mm 1.7 mm EIAJ-02 3.15 V to 6.3 V Yellow 3780266
C 4.7 mm 1.7 mm EIAJ-03 6.3 V to 10.5 V Yellow 3780267
D 5.5 mm 3.3 mm 0.9 mm EIAJ-04 10.5 V to 13.5 V Yellow 3780268
E 2.5 mm (3/32" submini plug) Black 3870005
F 3.5 mm (1/8" mini plug) Black 3875411
G 3.0 mm 1.1 mm Turquoise 3807935
H 3.4 mm 1.3 mm Orange 3870006
I 3.8 mm 1.1 mm Pink 3870007
J 5.0 mm 1.5 mm Red 3870004
K 5.0 mm 2.1 mm Purple 3807937
L 5.0 mm 2.5 mm Dark Green 3807938
M 5.5 mm 2.1 mm Navy 3807939
N 5.5 mm 2.5 mm White 3807940
O 5.5 mm 2.8 mm Brown 3780269
P 5.5 mm 3.8 mm 1.8 mm Not Specified 3802153
Q 6.3 mm 3.0 mm Yellow-Green 3780270
R 6.9 mm 4.2 mm 0.7 mm Not Specified 3912655
S 5.5 mm 1.5 mm Gray 3875405
T 6.5 mm 4.3 mm 1.4 mm EIAJ-05 13.5 V to 18.0 V Yellow 3875406
U 6.5 mm 4.1 mm / 3.10 mm 1.0 mm Light Yellow 3875407

See also


External links

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