The proliferation of scalable tactical equipment has driven the need for field configurable power-distribution systems. A stacking-interconnect technology has been developed that utilizes the same mating interfaces and locking mechanisms as standard MILDTL- 55181 connectors without the logistics planning and storage space requirements of Y-cables and power distribution panels.

Stacking connector mated to a power source and a “piggybacked” QPL connector sharing power.
The scope section of the MIL-DTL- 55181 detail specification defines “…a series of center-lock coupling screw, waterproof, polarized, multi-contact, intermediate power connectors for interconnection of power and control circuits on electronic equipment” for use by all departments and agencies of the Department of Defense.

This specification defines three insert arrangements that provide configurations with four 12-AWG contacts, nine 20- AWG contacts, or eighteen 20-AWG contacts. The 12-AWG contacts are rated at 35 amps and are used to provide power connections. The 20-AWG contacts are rated at 7.5 amps and have been used to facilitate power or data connections.

Five different cable sizes are defined ranging from .343 to .593 inches in diameter. Since the initial specification, increased data rates have necessitated the use of shielded cables and consequent inclusion of connector requirements to handle the shielded cables.

MIL-DTL-55181 connectors have been deployed in over one-half-million SINCGARS (Single Channel Ground and Airborne Radio System) radios. Subsequent adoption of these connectors has included a wide range of software- defined-radio platforms that have included the JTRS (Joint Tactical Radio System). These rugged and versatile connectors have also been used in power supplies, surge suppression systems, and power amplifiers.

The function of the stacking connector receptacle- mating pins and coupling screw is the same as QPL connectors.
Distributing power for tactical equipment has been facilitated by Y-cables but this scalability did not come without complications. Logistics planning was required to assure that the correct quantity of cables, additional routing and securing needed to ensure that the Y cables did not get in the way when in use, and dedicated pre and post deployment storage space were available. In addition, the length of the cable, and location of the “Y” splice, can vary from application to application and precluded standardizing cable management.

Recognizing the inherent complications of using “Y” cables, a defenseindustry prime contractor issued an RFQ in support of a U.S. Army program that incorporated two SINCGARS radios that would be powered from a common receptacle. The prime contractor specified a new technical challenge in the RFQ; the power sharing would be accomplished “with no extra parts needed and no parts left over”. This stipulation precluded the use of “Y” cables and power distribution panels.

In response to these new requirements, Eaton’s Cooper Interconnect business developed the MIL-DTL-55181 compliant stacking connector. This new interconnect solution shares the same mating interface and locking mechanism as standard M55181 connectors. The internal contacts were re-engineered to provide pass through power contacts that are accessible when the back cover is removed, enabling a second power cable to mate in the traditional fashion.

Critical requirements for this new product included development of an uncoupling mechanism that maintains uninterrupted mechanical and electrical connections to the primary device being powered while the back cap of the connector is removed to access the secondary receptacle contacts to power another device.

Another essential feature was the capability for field deployment without the need for any equipment retrofitting. Since the “plug” side of the stacked connector mates directly to the receptacle of the power source and the “receptacle” side of the stacking connector is compatible with QPL plugs and other stacking connectors, there is no need for cable or connector retrofitting on any equipment either sourcing or sharing power.

Back view of stacking connector depicts passthrough pins that enable power sharing with another connector.
Usability goals included maintaining the form-and-fit compliances of the QPL MIL-DTL-55181 connector to provide intuitive familiarity with the new connector in the field. The use of MIL-DTL- 55181 style solder lugs and cable-retention hardware facilitated attachment to equipment cables, on an OEM basis or depot-level retrofitted, without requiring any installation training or documentation specific to the stacking connector.

Due to the high number of mating cycles that this connector could experience in the field, a 500 engagement-cycle test was performed in addition to the MIL-DTL-M55181 electrical performance, shock, vibration, salt fog, humidity, and leak tests. The results of this extensive testing confirmed that the stacking connector would provide the necessary performance in mission-critical applications.

MIL-DTL-55181 connector deployments encompass an extremely broad range of harsh-environment applications ranging from fixed assets to ground mobile and manpack. When used in any of these applications, users need to confirm that the total power consumed by equipment sharing a receptacle should not exceed the maximum power rating of that receptacle.

In addition to the original 55181/3- 0X configuration, M55181/1-0X (4 socket) and M55181/7-0X (19 pin) versions have been developed. While the M55181/1-0X version is essentially the same as the M55181/3-0X in that it is used for power splitting, the M55181/7- 0X connector is typically used for data and the application use is to split two audio channels independently.

Subsequent development includes COTS versions, and a COTS adaptor series for shielded cables and dual-entry shells. These products support all of the standard cable sizes used with MIL-DTL- 55181 connectors.

Stacking Connectors have been successfully deployed on a variety of programs that have included the Force XXI Battle Command Brigade and Below (FBCB2) and Joint Tactical Radio System (JTRS) Network Integration Kit (NIK). In addition, the connector has found uses when adding additional capabilities to other vehicles such as Army ambulances being outfitted at Tobyhanna Army Depot.

This article was written by Peter Milstead, Director Mil/Aero Product Marketing, Eaton’s Cooper Interconnect business (Camarillo, CA). For more information, Click Here .