Protect Unmated DC Power Inputs with IP68 Sealed Barrel Jacks

For electronic devices and systems that spend much of their lives unplugged, the DC power input can be a weak point in reliability. An exposed jack can be vulnerable to spray, dust, and other environmental hazards. These conditions can pose unacceptable risks to portable and battery-powered systems, including test equipment, medical devices, and tactical gear.

This is particularly problematic for systems that rely on the classic barrel plug ecosystem with its abundance of commodity offerings. While designers can add ingress protection to barrel plug interfaces, doing so can reduce the benefits of this standardized approach. The challenge is protecting against environmental hazards while preserving the simplicity and convenience of the basic barrel plug.

This article explores the challenges unmated sealing presents for designers of electronic systems. It then introduces DC barrel power jacks from Switchcraft and shows how they can be used, along with compatible power plugs, to address these challenges.

How to protect a DC power barrel jack when not in use

Barrel plugs have long been the default choice for DC power delivery in portable equipment, with good reasons. They are simple, durable, and easy to design into a circuit. They support relatively high power delivery and are straightforward to use. Most importantly, they are easy to connect and disconnect and can withstand thousands of mating cycles.

However, conventional barrel plugs are not known for their environmental resilience. This can be a concern for equipment that might travel outdoors, encounter industrial dust or grit, or be subjected to washdowns or fluid submersion.

Fortunately, there are many ways to protect a barrel connection against environmental hazards. Protective overmolds, locking mechanisms, and other adaptations can provide a sealed connection between the plug and jack. When the device is unplugged, solutions such as dust caps can protect the unmated jack.

However, these solutions come with their own tradeoffs. For one thing, modifications to the conventional barrel plug design can reduce the flexibility that makes these connectors attractive in the first place. A bigger concern is what happens when the device is unplugged. Attachments such as dust caps must be applied every time the connection is unmated, leaving opportunities for human error. Plus, these add-on solutions may not offer sufficient protection against immersion or other environmental hazards.

For equipment that is frequently left unplugged, it would be advantageous to seal the jack itself. This way, protection does not depend on the use of a specialized barrel plug or on user behavior.

What are sealed, unmated DC power barrel jacks?

Switchcraft’s sealed unmated DC power jacks (Figure 1) were designed to meet this need. They use a novel design with a silicone housing and an epoxy potting that provides continuous ingress protection, even when no plug is connected. The jacks meet IP66, IP67, and IP68 requirements per IEC 60529, meaning that they protect against dust, water jets, and immersion in liquids.

Figure 1: Shown is a fully sealed, unmated DC power jack that can accept widely used barrel plugs. (Image source: Switchcraft)

The jacks achieve this ingress protection in two ways. First, when the mounting nut and washer are tightened against the panel, the silicone housing compresses against the opposite surface, forming a gasket-like seal around the mounting hole. Second, the epoxy potting on the termination side blocks moisture from entering through the solder lugs or printed circuit board (pc board) pins, closing another potential leak path. The combination of a compressed silicone interface at the panel and potted terminations at the rear provides continuous protection, regardless of whether a plug is connected.

Any water that enters the barrel opening can simply be blown out, and the jack left to dry. This makes the jacks a good fit for applications that require frequent cleaning. In medical applications, for example, devices can be thoroughly sanitized and returned to service with minimal downtime.

An added benefit is that none of this comes at the cost of compatibility. The jacks retain a standard barrel interface that can accept standard barrel plugs. For more robust locking connections, the jacks also feature a 5/16-32 NEF-2A threaded bushing compatible with Switchcraft’s Z series DC power plugs. This level of interoperability maximizes design options and benefits end users by allowing them to use any standard AC-DC adapter, eliminating the need to keep track of specialized equipment.

The jacks are rated to 24 V_DC at 5 A with standard materials, or up to 7.5 A with high-temperature materials. Every jack also includes an internal shunt switch that allows automatic switchover between power sources. This simplifies the circuitry needed to switch from a battery to external power when a charger is connected.

The jacks’ mechanical life is rated at 5,000 insertion/withdrawal cycles, ensuring longevity across many charging periods. The jacks are rated for an operating temperature range of -55°C to +85°C with standard materials or -40°C to +105°C for the high-temperature version, providing options for harsh environments.

Sealed unmated DC power jacks compatible with standard barrel plugs

The jacks are available in three common center-pin sizes of 1.3, 2.0, and 2.5 millimeters (mm), with termination options of solder lug, right-angle pc board mount, or straight pc board mount. A typical example is the 732AU (Figure 2). This 1.3 mm jack uses a solder lug termination, which is a natural choice for hand-wired assemblies and low-volume builds where pc board termination is impractical.

Figure 2: The 732AU solder lug sealed jack provides a straightforward power interface for hand-wired assemblies. (Image source: Switchcraft)

The 732AU can be paired with a standard plug or with the 860Z barrel plug (Figure 3) from Switchcraft’s Z series lineup. The 860Z features a 1.3 mm center pin and is compatible with the commodity plug ecosystem. However, the Z series adds features worth highlighting for applications that require more than a basic power connection.

Figure 3: The 860Z barrel plug features a 1.3 mm center pin and is compatible with the commodity plug ecosystem. (Image source: Switchcraft)

Highlights of the Z series include a touch-proof and scoop-proof design, with a recessed center contact that creates a “first make, last break” ground connection. The outer sleeve engages before the center pin on insertion, and the center pin disengages first on removal, reducing the risk of arcing during hot-plug events. The plugs also feature a larger cable clamp that accommodates cable diameters from 3.2 to 5.3 mm, providing better strain relief for the heavier cable assemblies that ruggedized equipment often uses.

Board-mount DC power barrel jacks with locking connector options

The 722RAU (Figure 4) demonstrates the right-angle pc board mount option. A right-angle jack is useful where board-level space constraints or panel orientation require a low-profile, perpendicular connection between the panel and the pc board.

Figure 4: The 722RAU DC barrel jack uses a 2.0 mm center pin and a right-angle pc board mount termination. (Image source: Switchcraft)

The 722RAU uses a 2.0 mm center pin and is compatible with Z series plugs, including the locking S760KZ (Figure 5, left) and the non-locking S760Z (Figure 5, right). These two options illustrate another key feature of the Z series plugs: most models have locking variants equipped with a coupling ring. These rings use the same 5/16-32 NEF-2A threading as the jacks, allowing end users to achieve secure mating with a simple twist-on, twist-off mechanism.

Figure 5: The S760KZ (left) and S760Z (right) demonstrate the Z series options for locking and non-locking barrel plugs, respectively. (Image source: Switchcraft)

The floating, self-aligning lockring threads onto the jack’s exposed bushing, securing the connection against vibration and accidental disconnection. The floating design allows the lockring to find the thread even if the plug body is slightly misaligned with the jack, improving mating reliability in blind or gloved-hand installations. Once engaged, the threaded connection resists the pull-out forces that a tethered cable can apply during normal handling.

Long-bushing DC power barrel jacks for thick panels

A final example of the sealed unmated jacks is the PCL712AU (Figure 6). This jack uses a 2.5 mm center pin and terminates with a straight pc board mount. It demonstrates one of the family’s key features: the availability of jacks with long bushings. Compared to the short bushings, which extend only 4.6 mm from the jack body, the long variant extends 7.1 mm. This exposes enough thread to support use with thicker panels.

Figure 6: The PCL712AU features a long bushing and a straight pc board mounting termination. (Image source: Switchcraft)

The PCL712AU can be paired with the 761KZ (Figure 7), a 2.5 mm locking plug. Together, this pairing provides a robust option that is suitable for tactical gear, transportation equipment, and other applications that require a secure, locked connection.

Figure 7: The 761KZ locking plug uses a floating ring to enable a locked connection to the jack. (Image source: Switchcraft)

Conclusion

Designers of portable and battery-powered equipment no longer have to choose between environmental protection and the convenience of the barrel-plug ecosystem. Switchcraft’s sealed unmated DC power jacks provide IP68 protection even when a device is unplugged, while preserving full compatibility with standard barrel plugs. Pairing these jacks with the Z series plugs delivers additional safety features and locking options, giving designers a wealth of options for equipment that will travel into diverse settings.