Heat is the silent killer of outdoor electronics. Last quarter, SanJun took an OEM call from a DC fast-charger integrator whose 160 kW unit was throttling at 38 °C ambient — seven weeks before summer peaks. The fix was not a bigger fan or a thicker heatsink. The fix was a sheet metal redesign of how air entered, mixed and left the cabinet. This article walks through four anonymised thermal case studies where SanJun rebuilt the chassis, not the electronics, and what we changed in each one.
Why Sheet Metal, Not Heatsinks or Fans
Off-the-shelf heatsinks and catalog fans solve one heat path at a time. An outdoor enclosure sees four problems at once — internal electronics heat, ambient solar gain, humidity condensation, and a pressure differential from wind. Custom sheet metal is the only way to integrate the four into one IP-rated structure. At SanJun we treat every thermal program as a flow problem first, and a materials problem second. Steel thickness, weld geometry and powder coat are downstream of an airflow plan that has been validated against the unit's worst-case operating envelope.
Most of our thermal projects go through the same three-step handoff:
- 24-hour DFM review of the customer CAD. We red-flag weld positions that block airflow, louvers that face prevailing rain, and bracket layouts that trap hot air near the heat source.
- Rapid prototype in 5–10 days. Sheet metal parts move through laser, brake press, MIG/TIG weld and powder coat; sample chassis are thermal-cam tested inside the customer's actual electronics.
- Production with the same tooling. No transfer to a second supplier for serial runs — same line, same fixtures, same sealing procedure.
Case 1 — 160 kW DC Fast Charger: Eliminating Summer Derating
An EU EVSE integrator came to us with 38 °C derating on a 160 kW outdoor unit, IP54 rated, mounted on a sun-exposed truck stop canopy. The OEM had already added two more fans — no change. Inside the cabinet the power modules were sitting at 78 °C with 22 °C ambient, well over the 70 °C derating threshold. Air was moving, just in the wrong direction: hot exhaust was recirculating across the inlet.
SanJun's changes:
- Replaced flat side vents with angled, rain-resistant louver arrays. Intake area gained 18% net flow at the same opening footprint, and the angle dropped direct sun load on the louvers by 40%.
- Added an internal sheet metal baffle between inlet and exhaust. Hot exhaust air is now pulled directly to the rear of the cabinet, isolated from the inlet plenum.
- Tuned the front-panel cutout pattern for chimney effect. Lower intake + upper exhaust path lets thermal buoyancy do half the work on calm days.
Result: at the same 38 °C ambient and same fan power, internal module temperature dropped from 78 °C to 64 °C. The unit held full 160 kW output through the August peak.
For EV charger enclosures, see our EV charging pile enclosure design guide.
Case 2 — IP65 Outdoor BESS: Cold-Plate Integration Without Breaking the Seal
A North American battery integrator specified IP65 outdoor cabinets for a 215 kWh rack-dense BESS deployment in southern California. The interior battery wall was running 36 °C with 32 °C ambient — within spec but only 4 °C below the manufacturer's thermal warning. Adding a fan was off the table (IP65) and adding a refrigerant loop was off the budget. The customer wanted a passive improvement that would work across all four seasons of operation.
SanJun's changes:
- Folded-in structural mounting frames for a liquid cold plate. A coolant loop was added to the battery wall, with quick-connect fittings accessible behind the bottom service panel. Cabinet IP65 was preserved — all coolant penetrations are below the seal plane.
- Two-compartment internal partition. High-voltage bus bars and battery modules are physically separated by a sealed sheet metal wall. Heat conduction between them is minimized while EMC isolation is preserved.
- Dual powder coat on the chassis exterior. A zinc-rich primer + 80 μm polyester topcoat for marine-coast-grade corrosion resistance at a desert solar site.
Result: battery wall temperature dropped to 28 °C with the cold plate operating. IP65 verified by independent lab. The same BESS cabinet platform was reused across five subsequent deployments with different cold-plate geometries — no welding changes were needed.
For the broader BESS thermal toolkit, see our energy storage cabinet enclosure guide.
Case 3 — Outdoor High-Brightness Display: Solar Load Compensation
A smart-city integrator deployed 32-inch, 3000-nit outdoor displays at a Middle East bus station. Standard surface temperature of the LCD panel was running 67 °C during summer afternoons, triggering brightness rollback to 1500 nits — visibility was lost and the customer received complaints within a week. The chassis itself was okay; the problem was solar gain on the black rear panel plus the high-brightness backlight heat combined.
SanJun's changes:
- Double-walled aluminum sunshade. Outer aluminum shell with a 6 mm air gap to the inner chassis — drops direct solar load by ~55% on the rear panel. We work from the same method in our outdoor sunshade and hood design guide.
- Cross-flow heat sink behind the LCD. Folded aluminum fin stack bonded to the inside rear wall, channels heat from the backlight into the exhaust path.
- Temperature-controlled DC fan tray. Two 80 mm fans activate only above 50 °C internal — silent most of the day, full convection when needed.
Result: rear panel surface temperature fell from 67 °C to 48 °C. Display held 3000 nits through the afternoon. The customer rolled the design out across 80 subsequent stations in two further cities.
Case 4 — 2U High-Density Server Chassis: Static Pressure, Not Volume
A Taiwanese telecom OEM asked us to redesign the front bezel of a 2U rack chassis used for 5G edge computing. Their existing front panel was a thin hex-perforation pattern that worked at low density but choked at the latest CPU generation — fans were operating at 90% speed to maintain cooling, with an acoustic signature that was failing the customer's noise spec.
SanJun's changes:
- Redesigned bezel with high-open-area perforations. Same 1.5 mm steel thickness, but the hexagonal cell pattern was reshaped from 3 mm cells to 5 mm cells in a tighter pitch. Net open area increased from 38% to 58%.
- Internal air-guide baffles. Folded sheet metal guides direct high-velocity air through the CPU and VRM zones — air now arrives at the heat sink with a defined velocity profile instead of diffusing from the bezel.
- Heat sink mounting pads. Stamped reinforcement at the heat sink attachment points, eliminating flex at high static pressure.
Result: fan duty cycle dropped from 90% to 65% at the same thermal load. Acoustic noise dropped from 56 dBA to 49 dBA. The CPU thermal margin grew from 6 °C to 12 °C — enough to support a 15% TDP increase on the next platform refresh.
For more on vent geometry, see our perforated vent pattern cooling guide.
How to Start a Thermal Enclosure Project
A well-scoped thermal program has three documents ready before DFM review:
- Internal heat dissipation. Worst-case power per heat source, summed with 20% margin.
- Ambient envelope. Min and max operating temperature, humidity class, solar exposure.
- Protection target. IP or NEMA rating, plus any dust or chemical exposure beyond water.
Send us those three plus your chassis envelope and we will return a thermal concept — baffle layout, vent pattern, fan spec, cooling type — within 24 hours.
Frequently Asked Questions
Why is sheet metal design critical for thermal management in sealed outdoor enclosures?
A well-engineered thermal management enclosure integrates air baffles, angled louvers, double-wall solar shielding, cold-plate brackets or heat exchangers while preserving structural integrity and environmental protection. Sheet metal is the only mass-manufacturable material that can be folded, welded and coated to host all of these features in one chassis at OEM cost.
What is the difference between air cooling and liquid cooling in BESS enclosures?
Air cooling moves heat with forced or natural airflow — simple, low-cost, limited thermal density. Liquid cooling uses cold plates and coolant loops to carry heat out of dense battery packs. For high-density outdoor BESS, liquid cooling achieves lower cell temperature spread and supports faster cycling, at the cost of plumbing, coolant and leak risk.
How does enclosure thermal design prevent throttling in high-power DC fast chargers?
Effective EV charger thermal management establishes segregated intake and exhaust paths, blocks hot-air recirculation with internal baffles, and delivers cool air directly onto the power-conversion modules. On a 160 kW outdoor unit, replacing flat vents with angled, rain-resistant louver arrays typically recovers 10–15 °C of headroom and prevents derating in mid-summer operation.
Can thermal management be added without breaking IP65?
Yes. IP65 thermal management typically relies on sealed dual-chamber layouts, closed-loop air-to-air heat exchangers, or sealed-cabinet + external cold-plate designs. The cooling loop stays outside the sealed barrier while heat is conducted through the wall — electronics see no airflow and no moisture.
What should buyers evaluate when choosing a thermal-enclosure manufacturer?
Look at four things: thermal design experience across EV / BESS / display / server workloads, DFM support with 24-hour drawing feedback, prototyping speed (sample in days, not weeks), and precision build records (weld integrity, sealing, finishing). A thermal-only enclosure without environmental sealing is just a heatsink in a field of failures.
Conclusion
The four cases above share one outcome: the chassis was the bottleneck, not the electronics. A good thermal-enclosure manufacturer solves airflow, sealing and structure together — not as three separate vendors. If you have a thermal program that is failing in the field, the fastest answer is almost always a 24-hour DFM review of your current chassis geometry, not a new electronics revision.
Send us your worst-case dissipation, your ambient envelope and your IP target. SanJun will return a thermal concept within 24 hours.