Inside a Rugged Peli Case PC: Conquering Heat and Shock in a Hermetically Sealed Box

Inside a Rugged Peli Case PC: Conquering Heat, Shock, and Hermetic Sealing

Building a high-performance computer into a Peli case is an engineering paradox. The very physical properties that make an injection-moulded copolymer case indispensable in the field – watertight sealing, extreme impact resistance, chemical inertness, and structural isolation – are the exact opposite of what high-power computing components demand: active ventilation, rapid heat dissipation, and structural rigidity.

Standard consumer motherboards or off-the-shelf industrial PCs bolted into pick-and-pluck foam inevitably fail in real-world deployments. Copolymer polypropylene is an exceptional thermal insulator. Trapped inside a hermetically sealed IP67 enclosure, a 65W processor alongside a wide-input power supply and expansion cards will turn the interior into an oven within minutes.

To survive field diagnostics, defence operations, and offshore telemetry, a “System-in-a-Case” cannot simply be treated as an off-the-shelf PC secured inside a plastic box. It must be engineered from the ground up as an integrated thermodynamic and kinetic system.

1. Shock & Vibration: The Engineering Behind Corner Elastomeric Mounts

In mobile field deployments, a transit case PC faces relentless dynamic stress: rough transit in 4×4 flatbeds, generator vibration, and sudden drop shocks (governed by standards like MIL-STD-810H Methods 514.8 and 516.8).

While aerospace-grade wire-rope isolators exist, the industry workhorse for compact, high-reliability case PCs is the elastomeric sandwich mount (commonly known as cylindrical rubber bobbins or corner vibration mounts).

Placing elastomeric mounts at the corners between the case’s mounting frame and the internal aluminium chassis isolates delicate electronics, but sizing them requires careful calculation:

Shear vs. Compression Loading

Standard cylindrical rubber mounts excel under compression (vertical loads). However, when a field technician drops a case on its side or end, those corner mounts experience high shear loads. Rubber-to-metal vulcanised bond lines are far weaker in shear.

• The Solution: Specify captive or fail-safe cup mounts. These feature an interlocking internal metal collar: even if the elastomeric material shears entirely during a catastrophic impact, the mechanical interlock prevents the internal chassis from breaking loose inside the case.

Calculating Durometer (Shore A) and “Sway Space”

Selecting mount durometer involves balancing shock attenuation with allowable deflection:

• Too Stiff (70+ Shore A): The mounts act as rigid conduits, passing high-G impact shocks directly to PCB solder balls and M.2 slots.
• Too Soft (30–40 Shore A): Under severe drop acceleration, the mounts over-deflect, allowing the chassis to violently strike the floor or walls of the outer case (“bottoming out”).
• Design Rule: Always factor in a minimum 10–15mm dynamic “sway space” clearance envelope around the entire chassis perimeter.

Temperature Limits: Neoprene vs. Silicone

Standard natural or neoprene rubber degrades rapidly when deployed across industrial extremes. Below -10°C, standard rubber undergoes glass transition, turning brittle and transmitting 100% of shock energy directly into the electronics. For true -20°C to +60°C military and offshore operating ranges, specify high-damping silicone or fluorosilicone elastomers, which maintain consistent damping ratios across the entire operating window.

2. Thermal Dissipation: Cooling a Hermetically Sealed Box

When the case lid is closed and latched to maintain IP65 or IP67 ingress protection, forced external air exchange is impossible. Convection inside an untreated case rapidly reaches thermal saturation.

3. Power Conditioning & Field Ingress

Field computing gear rarely enjoys clean mains power. Between unstable generators, dirty vehicle 24V batteries, and alternator load dumps, raw power kills embedded electronics quickly.

• Wide Input Isolation: Internal power architectures must accept a wide DC range ( backed by galvanic isolation to sever ground loops.
• Surge Suppression: Protecting against ISO 7637-2 and MIL-STD-1275 automotive transients requires multi-stage front-end suppression—incorporating transient voltage suppression (TVS) diodes, common-mode chokes, and active overvoltage shut-off circuits.
• Hermetic I/O: Every external interface must transition through the panel via IP67-rated sealed circular connectors (such as Amphenol, Souriau, or Neutrik industrial bayonets) backed with die-cut closed-cell silicone perimeter gaskets.

4. The Critical Role of Pressure Equalisation

To eliminate this without compromising ingress ratings, custom case PCs integrate an automatic hydrophobic/oleophobic membrane purge valve (such as a Gore-Tex membrane vent). This allows continuous gas equalisation while presenting an impenetrable barrier to moisture, oils, and particulate down to IP67 immersion limits.

Engineering Checklist: Built for the Real World

Subsystem	Baseline Consumer In-a-Box	Engineered Industrial Case PC
Mechanical Shock	Pick-and-pluck foam (breaks down over time)	Captive elastomeric mounts with 15mm sway clearance
Thermal Dissipation	Trapped ambient air / fan recirculating heat	Sintered heat pipes routed to structural aluminium top-deck heatsink
Chassis Assembly	Direct chassis-to-plastic sheet metal screws	Floating 6061-T6 aluminium sub-cage with strain-relieved locking headers
Power Input	Unprotected 12V DC brick	Isolated wide-input ($9\text{–}36\text{V}$) with active MIL-STD-1275/ISO 7637-2 surge suppression
Environmental Ingress	Cutouts with foam tape	IP67 bayonet I/O, custom silicone gaskets, and continuous membrane purge vents

Need a Custom Transit-Case PC Built for Extreme Field Conditions?

At BVM, we design, prototype, and manufacture bespoke transit-case computing systems tailored to your exact application—from military-grade field diagnostic units and offshore test rigs to mobile edge AI stations. Speak to our engineering team today to discuss your project requirements, thermal limits, and environmental compliance targets.