Power supply enclosure cooling and temperature checks

Calculate the power supply’s losses at its actual electrical load, then check its permitted mounting orientation and local ambient temperature. A fan is needed only when the complete assembly cannot meet those limits without one. Supply wattage alone cannot answer that question. Start with a heat estimate, preserve the manufacturer’s clearances, and verify temperatures with the enclosure closed under the worst operating conditions.

What you need

Collect these inputs before choosing the enclosure or adding ventilation:

• The supply’s installation instructions, efficiency data, derating curves and cooling requirements.
• Continuous output current, peak current and the duration of each operating condition.
• Maximum surrounding air temperature, including heat inside a machine stand or compartment.
• Losses from every other component installed inside the same enclosure.
• A dimensioned layout showing terminals, cable bends, clearances and the intended airflow path.
• Suitable temperature logging equipment and a safe method for loading the supply.
• The installation’s requirements for water, conductive debris, coolant and electrical approval.

Electrical protection remains a separate design task. The article on installing a power supply and relay inside a small enclosure covers the associated enclosure and wiring considerations.

For installation and measurement setup, isolate all energy sources, apply the required lockout procedure, and verify absence of voltage. Use qualified electrical work practices throughout.

Work from electrical load to enclosure cooling

1. Establish the supply’s electrical output load.

   Use output voltage multiplied by output current, not the motor’s mechanical output rating. At 24 V DC and 5.4 A, the supply delivers about 130 W electrically. A motor marked 130 W may require more electrical input because the motor and controller also have losses.

   Record acceleration, stall protection and controller demand separately from normal running load. Check these against the supply’s overload capability and the motor-control design. An average load below the supply rating does not establish acceptable peak performance.

2. Convert efficiency into heat loss.

   Calculate supply loss using P_loss = P_out × (1 / efficiency − 1). Enter efficiency as a decimal and use data for the applicable input voltage, load and temperature.

   For 130 W output at 90% efficiency, input power is about 144.4 W. The difference, approximately 14.4 W, becomes heat in the supply. At 85% efficiency, the same output produces approximately 22.9 W of loss.

   A 180 W supply does not release 180 W inside the enclosure merely because that is its capacity. Likewise, operating at a particular percentage of capacity does not automatically require forced air. The installation instructions and derating curve decide what cooling conditions are acceptable.

3. Count everything that heats the enclosure.

   Add losses from internal relays, controllers, indicator devices and other equipment. Include resistive heating from wiring and connections where significant. If the motor and speed controller are outside, their losses are not part of the enclosure’s internal heat total.

   Do not calculate supply loss by subtracting measurements from unrelated operating conditions. If efficiency data are unavailable, use an appropriate power analyzer and simultaneous input/output measurements through a qualified test arrangement. AC input requires real power in watts, not simply voltage multiplied by current.

4. Set the allowable internal temperature rise.

   Identify the lowest applicable temperature limit among the supply and neighboring components. Apply each device’s derating rules at its local ambient temperature. The room temperature is not necessarily the temperature of air entering the supply.

   For example, suppose the supply permits the required load at a local ambient of 113°F [45°C]. With surrounding enclosure air at 95°F [35°C], only 18°F [10°C] of temperature rise remains before that limit. This example is a design budget, not a universal supply limit. Reserve additional margin for uncertainty and service conditions.

   Follow the detailed method for checking control cabinet temperature limits when devices specify different ambient, case or terminal limits.

5. Lay out the supply before selecting the box.

   Preserve the specified orientation and clearances around vents, heat sinks and terminals. Allow space for cable bends, guards and service access. Do not assume a perforated supply can touch the enclosure wall because its overall dimensions fit.

   For example, the 12 x 10 x 8 in stainless wall-mount enclosure has outside dimensions of 12 x 10 x 8 in (H x W x D). Those dimensions do not establish mounting-panel-to-door clearance or thermal capacity; verify the actual installation drawing.

   Our wall-mount enclosures are manufacturer-rated NEMA 4X-type / IP66; not UL listed. Material alone does not establish electrical safety or adequate cooling. A polymer enclosure still requires appropriate electrical, fire and mechanical suitability. Metal parts require the protective bonding described in the enclosure grounding and bonding guide.

6. Check whether the closed enclosure can reject the heat.

   Use the total internal losses, surrounding temperature and effective enclosure surface area in the enclosure heat calculation guide. Account for walls blocked by mounting surfaces and nearby equipment. Do not assign cooling capacity from internal volume alone.

   A supply inside a shallow machine compartment must reject heat through both its enclosure and the surrounding compartment. Use the compartment temperature as the relevant external condition. The article on nested enclosure heat buildup explains why unrestricted room air is the wrong assumption for that arrangement.

   An internal circulation fan can reduce temperature differences, but it does not remove heat from the box. Similarly, a supply’s built-in fan does not guarantee adequate enclosure ventilation.

7. Add ventilation only when the environment permits it.

   For ordinary air near sea level, a first airflow estimate is CFM ≈ 1.76 × heat loss in W / air temperature rise in °C. If total losses are 25 W and the permitted ventilation-air rise is 10°C, the estimate is approximately 4.4 CFM through the enclosure.

   That is delivered airflow, not a fan’s unrestricted rating. Filters, guards, inlet restrictions and the supply itself create resistance. Select from the fan’s performance curve and verify the complete airflow path. Avoid an inlet and outlet arrangement that lets air bypass the supply.

   Do not draw machining swarf or conductive dust through exposed electronics. An ordinary dust filter is not proof against fine conductive contamination or coolant mist. Where contamination makes ventilation unsuitable, retain a closed design and assess a larger enclosure, a different supply or closed-loop cooling. The fan, air conditioner and heat exchanger comparison explains those choices.

Verify temperatures before release

Install temperature sensors with the equipment de-energized. Secure them clear of terminals, moving parts and required electrical clearances. Use documented measurement points; do not attach sensors to exposed live circuitry or modify internal supply components.

Measure the surrounding enclosure air and the local air entering the supply. Measure case or terminal temperatures only where the manufacturer provides an applicable limit and safe measurement method. A warm enclosure wall cannot establish that internal components are cool enough.

Test with the door closed, cable entries completed and the actual installation orientation reproduced. Run the highest sustained electrical load and representative operating cycles. Allow temperatures to stabilize rather than accepting a brief successful run.

Repeat at the highest specified surrounding temperature or use an appropriate controlled test arrangement. Do not simply add a room-temperature rise to a hotter ambient without checking derating and cooling behavior.

Record these release checks:

• Local ambient and specified measurement points remain below their applicable limits, with documented margin.
• Output voltage remains acceptable throughout the operating cycle.
• No thermal shutdown, unexpected restart or overload cycling occurs.
• Required airflow remains available with the intended filter and maintenance allowance.
• Adjacent wiring, connectors and components also meet their temperature limits.

Thermal shutdown is fault protection, not a normal temperature-control strategy. If cooling failure creates a hazard, address detection and the machine’s safe response in the control design.

Mistakes that cost the rating

Cutting a fan opening changes the enclosure assembly. Do not carry the original protection claim over to an unassessed fan, filter or grille installation. Specify accessories suitable for the required protection and have the complete arrangement reviewed.

A rain hood does not automatically provide hose-down protection. Likewise, a filter that catches visible chips may still admit fine conductive particles. Keep the environmental assessment separate from the airflow calculation.

Other installation errors can undermine both sealing and cooling:

• Oversized cable openings or glands outside their permitted cable diameter range.
• Unsealed mounting penetrations through the protected enclosure boundary.
• Cable bundles blocking the supply’s inlet or outlet.
• Loose wiring trapped across the door gasket.
• Drilled debris left inside the supply or around its terminals.

Use the cutouts, glands and HMI windows guide for penetration details. Do not add an improvised drain or leave an unused opening as a cooling shortcut.

What to specify after verification

Specify the enclosure around the proven layout and heat-removal method, rather than selecting a box around supply wattage. Keep the electrical approval requirement explicit; the enclosure rating alone does not approve the completed assembly.

Use the enclosure selector once usable dimensions and environmental requirements are established. A dimensional match still requires the thermal checks above. For a layout needing specific dimensions or penetrations, send those requirements with the drawing for custom enclosures.

Enclosures in this article

Questions