Interconnection
Beyond 38999 T
New technology is once again pushing connector development for military OEM’s, explains Nick Harper, managing director, ODU-UK Ltd
he de-facto connectors for military equipment have been the various MIL-DTL Standards, issued and controlled by the US Department of Defense (DoD), in particular the MIL-DTL 38999. However, these specifications traditionally lag behind the development of military equipment technology - just such a situation currently exists and another is emerging.
Where it all started
The history of the military 38999 connector is usually quoted as starting in the 1930’s, but in reality, the seeds were planted a decade earlier, when in 1923, California-based James Cannon developed the four-pronged M plug - turning the ‘Cannon Plug’ into a generic name still in use today. Movie studios used them to allow their new electrical cameras to move around whilst shooting and subsequently used smaller versions in sound equipment. Then, in the 1930s, the U.S. DoD developed specifications of electrical connectors for military applications - the AN Series (Army & Navy). An early version was the ANSI 9634 (later the MIL-C 5015) which was very reliable for AC/DC power transmission. However, the smallest contact (size16) was not suitable for higher frequency signals. Due to this limitation, in the 1950’s the MIL-C 26482 (US Navy) and MIL-C 83273 (US Air Force) were both developed to accommodate size 20 contacts. In the 1970’s further development of electronic equipment demanded a connector with greater signal capacity, higher contact density and even smaller contacts - thus, the new MIL-C 38999 standard was created, supporting contacts down to size 22. Today, the connector known as the MIL-DTL-38999 has four unique sub-types: Series 1 Bayonet quick-disconnect Series II Low-profile bayonet Series III Stub-ACME triple-start screw-thread Series IV 90° quarter-turn ‘breech-lock’ These and their commercial variants are marketed today by many of the large global manufacturers in the connector industry.
62 September 2023 So, what has happened?
Well, after a long lag, technological demands have yet again, driven connector development. This time it has been the various Soldier Modernisation programmes that have needed much smaller and lighter connectors, as wearable devices now festoon the foot-soldier like a Christmas tree. On average a soldier must now carry 47kg, with a vest weight of 12kg, so clearly weight has become a major issue. As technology develops, the number of interfaces increases - but each piece of kit needs to be removable and replaceable - often at speed, whilst under fire.
At the same time, more protection is rightly demanded - so as body-armour increases, less space is available and the design conundrum continues, with weight (and power) the Achilles Heel for the equipment manufacturers and foot-soldier alike. These programmes have forced connector manufacturers to offer new designs - smaller and lighter than MIL-STD connectors, whilst still matching the performance & test methods.
What follows?
Soldier modernisation was the beginning, but the same problems that face the foot-soldier also occur inside the supporting military vehicle and broadly similar solutions will need to be applied, as traditional MIL-STD connectors do not offer sufficient space and weight savings to allow for the accommodation of more and more equipment inside the vehicle. There are many connector manufacturers in the military market place and ODU are certainly not the largest, but we believe that our strength lies in our flexibility, together with our commitment to helping our customers design and produce the best possible products. So, in order to expand our military business, we first of all wanted to ensure that our military connector, the ODU-AMC (Advanced Military Connector) Series, outperformed the existing MIL-STD connectors in three specific areas: durability, ingress protection, and size. We also identified two further areas of concern expressed by OEM‘s: high-speed data and connector locking selection - here are our results:
Components in Electronics Durability
The more durable the product, the longer it can remain in service - think about the routine, ordinary use of the product – repeated with realistic frequency. For example, LCD-display life (or half-life), is commonly measured in hours of use, with many capable of operating continuously for 10+ years. Similarly, key pads are measured in clicks, with a capability of millions of clicks - operational for decades. So, what about the connectors used on these systems?
Unfortunately, many are only capable of withstanding 500 mating cycles or less. Although there is no ‘standard-use’ case, it might be reasonable to assume that any electronic equipment that’s carried by a soldier will be connected/disconnected every day for at least half the year. So, depending on the choice of connector, many could be limited to less than two years of use before needing to be serviced.
If the application warrants a twist-lock or threaded mating system, two connector options appear to outshine the rest: MIL- DTL-55116 and ODU-AMC Series T connectors.
Ingress protection
Ingress Protection ratings [IEC standard 60529] rates the degree of protection provided by electrical enclosures against intrusion by body parts, dust and water. For example, IP67 requires that the device under test must
be capable of total immersion in water at a depth of 1 metre for a minimum of 30 minutes. However, many mil-spec connectors are not actually IP-rated, but instead reflect specific-use test standards. Therefore, we considered only whether or not the products have been tested to a standardised method for fluid ingress protection:
For MIL-DTL-55116 connectors, this is explicitly defined by the ‘water immersion’ requirement.
For MIL-DTL-38999 and Miniature 38999 connectors from the “altitude immersion” requirement.
ODU-AMC Threaded connectors are waterproof to IP6K9K at a depth of 20m for 2 hours.
Size
Flange-size represents a critical dimension, determining the minimum distance between
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