Introduction: A three-tier thermal matrix links 50 C full-load operation, 70 C derating, 5,000 m altitude, and measured enclosure temperatures to installation clearance decisions.
What Fanless Cooling Does and Does Not Mean
A fanless power supply transfers heat through its housing and surrounding air. Removing the fan eliminates a rotating part, reduces noise, and avoids drawing dust through the unit, but it does not remove the electrical losses that generate heat. The enclosure must still provide a path for air to absorb heat and leave without creating a hot pocket.
Conduction and Natural Convection
Internal heat moves to the case by conduction and then to nearby air by natural convection and radiation. Surface area, air temperature, airflow, and nearby obstructions control the process. A shallow open-frame unit can save volume, but the same density can make local air warmer.
Why Eliminating a Fan Does Not Eliminate Heat
At 100 W output and 88 percent efficiency, input power is about 113.6 W and estimated heat is 13.6 W. Efficiency varies with operating point, so this is a planning estimate. The conclusion is still direct: a fanless unit produces waste heat, and a panel without forced cooling must remove it through the enclosure or another thermal path.
Estimating Waste Heat from Output and Efficiency
Divide output power by efficiency to approximate input power, then subtract the output. Use the intended load and the matching efficiency basis. Do not combine a maximum output with a generic efficiency and present the result as a precise thermal model without validation.
An Arithmetic Example Based on Published Ratings
The table compares the 100 W class description with the 108 W arithmetic associated with 24 V and 4.5 A. Both rows use the published efficiency statement of above 88 percent only as an illustrative planning basis.
| Output condition | Efficiency basis | Approx. input power | Approx. heat load | Required caveat | Verification action |
|---|---|---|---|---|---|
| 100 W class description | Above 88%, typical | 113.6 W | 13.6 W | Efficiency depends on load point | Use current data and measure the enclosure |
| 108 W arithmetic at 24 V x 4.5 A | Above 88%, typical | 122.7 W | 14.7 W | Nominal output is not unconditional | Confirm rating conditions and apply derating |
| 81 W illustrative load at 75% | Above 88%, typical | 92.0 W | 11.0 W | 60 C interpolation is illustrative only | Replace with the actual curve and load |
The small difference between the two estimates does not answer the enclosure question. Heat load must be compared with surface area, allowable temperature rise, adjacent losses, and the ability of the cabinet to reject heat. Other controllers, transformers, and power resistors share the same internal air.
Reading the Manufacturer Thermal Specification
A thermal statement is useful only with its conditions. The example model is published for full load through 50 C, derating from 50 C to 70 C, and additional altitude derating. These values begin the review; they do not show that a particular enclosure stays inside the stated ambient range during production.
Rated Ambient Temperature
Ambient normally means the air around the product, not the room outside the cabinet. Measure near the supply, including above it, because warm air can stratify under the enclosure roof. A sensor on the door may report a comfortable value while the upper panel is much warmer.
Full-Load and Derated Operating Ranges
The specification permits full load to 50 C and then reduces capacity up to 70 C. The reviewer should follow the curve and installation instructions. Assuming full load at 60 C would replace the published derating with a project assumption.
Load Derating Between 50 C and 70 C
A linear curve from 100 percent at 50 C to about 50 percent at 70 C gives about 75 percent at 60 C. This is illustrative arithmetic, not a universal rating. Use the actual graph and confirm whether orientation or input voltage changes the permitted load.
Why the Actual Load Must Be Checked Against the Curve
An average load can hide peaks above the derated limit, and future devices can raise the duty after commissioning. Compare the maximum expected continuous load at the hottest enclosure condition with the curve. Review short peaks separately for voltage stability, protection, and recovery.
Altitude and Installation Conditions
The catalog states a 5 C ambient derating for each 1,000 m above 2,000 m. At 5,000 m, that corresponds to 15 C of additional ambient derating. Apply this with the other installation conditions and obtain manufacturer confirmation when the result is close to a boundary.
Additional Constraints That Require Manufacturer Confirmation
Confirmation is appropriate for unusual orientation, proximity to a heat source, a sealed enclosure without measured data, or operation outside published altitude limits. The query should include measured ambient, load profile, mounting, input voltage, altitude, and document revision.
Installation Clearance as a System Requirement
Clearance reserves space for natural convection, terminal access, and separation from adjacent materials. The drawing should show the complete zone, including ducts and labels, so maintenance does not block a nominal air path. Dimensions must come from the instructions for the supplied model.
Manufacturer Minimum Distances
The ABL2REM instructions distinguish horizontal and vertical mounting. The documented side spacing is 15 mm horizontally and 20 mm vertically, with 50 mm above and below in both configurations. These are product-specific requirements, not universal open-frame dimensions.
| Mounting orientation | Left and right side | Above | Below | Source basis |
|---|---|---|---|---|
| Horizontal | 15 mm | 50 mm | 50 mm | ABL2REM installation instructions and catalog |
| Vertical | 20 mm | 50 mm | 50 mm | ABL2REM installation instructions and catalog |
These figures apply when the remaining installation follows the instructions. A larger distance may be justified by a hot component or service policy. A smaller one should not be justified merely because the cabinet is compact.
Airflow Entry and Exit Paths
Natural convection needs cooler intake air and a clear route for warmed air to leave. A supply under a wire duct can satisfy a measured gap while sitting in a stagnant pocket. Check the rising air path and keep the upper escape zone free. Enclosure vents must also be assessed for dust and moisture.
Separation from Heat-Producing Components
Transformers, drives, braking resistors, and controllers can raise local air temperature above the cabinet average. Separation reduces convective and radiant coupling, but the required distance depends on the source. Use local sensors or thermal imaging and record both source and supply temperatures.
Wiring, Service Access, and Touch Protection
Clearance supports safe termination, testing, and inspection. Conductors need room to bend without loading terminals, and a technician needs space to reach a test point without contacting adjacent live parts. For an open-frame unit, the host enclosure and any guard must provide touch protection without blocking the thermal path.
Why Electrical Clearance and Thermal Clearance Are Different Questions
Electrical clearance addresses insulation, voltage, contamination, and contact risk. Thermal clearance addresses heat transfer and local air temperature. A barrier can improve one condition while worsening the other, so the layout should document both requirements and any accepted compromise.
A Three-Tier Thermal Risk Matrix
Risk tiers are useful when evidence is incomplete because they define the next action. The matrix does not replace the manufacturer curve or measured enclosure data.
| Risk tier | Ambient condition | Load condition | Installation condition | Evidence required | Required action |
|---|---|---|---|---|---|
| Low | Inside the published full-load range with margin | Maximum continuous load remains inside the curve | Clearances, orientation, and airflow follow the instructions | Sensor map, load ledger, revision, and test record | Retain evidence and review any design change |
| Medium | Near the derating zone or affected by local heat | Close to the curve or growth is expected | Nearby heat source or airflow is uncertain | Stabilized enclosure test plus the applicable curve | Improve airflow or load margin; escalate if margin is weak |
| High | Outside a published limit or unresolved altitude condition | Above the permitted load or transient behavior is unverified | Blocked clearance, orientation conflict, or missing instructions | Complete test and written manufacturer response | Redesign, select another format, or reject approval |
Low-Risk Installation Evidence
A low-risk condition has documented ambient and load values inside the continuous range, installation-sheet clearances, and a preserved convection path. The record identifies sensor locations, production duty, test date, and document revision. A design change requires the evidence to be reviewed again.
Medium-Risk Installation Evidence
A medium-risk condition approaches the derating zone, includes nearby heat sources, or cannot be characterized by stable airflow data. It also applies when load growth is expected or the temperature record comes from a short test. Improve instrumentation and confirm the curve before accepting the design.
High-Risk Conditions Requiring Redesign or Testing
High risk includes operation outside published ambient, altitude, orientation, or load assumptions. It also includes missing instructions or a conflict between the product page and installation drawing. Escalate to the manufacturer, redesign the thermal path, select another format, or perform a documented enclosure test. Missing evidence must not become a pass.
Verification Procedure for an Industrial Enclosure
The test should reproduce the installed cabinet, including production wiring, closed door, adjacent heat sources, and expected duty. An open bench does not establish enclosure performance. The procedure below creates a record that can be compared with the manufacturer documents.
Define Load and Ambient Conditions
Record the production load, room temperature, input voltage, connected devices, duty cycle, and enclosure cooling or heating. Define the worst credible operating case rather than a mild commissioning condition.
Measure Internal Enclosure Temperature
Place air-temperature sensors near the supply inlet and outlet, above the unit, near the cabinet top, and outside the enclosure. Avoid attaching the sensor to metal when air temperature is required. Record the sensor type and location.
Run a Thermal Soak Test
Operate the panel until temperatures stabilize at the defined load and ambient condition. Record the stabilization criterion, duration, door state, and any test changes. A short functional run may confirm voltage but not final enclosure temperature.
Record Voltage, Current, Temperature, and Location
The test record should allow an independent reviewer to reconstruct the result:
1. Input voltage and frequency at each steady-state sample.
2. Output voltage and current by load group.
3. Ambient temperature at each sensor location.
4. Supply surface temperature where the method permits.
5. External enclosure and room temperature.
6. Test duration, door position, and ventilation state.
7. Any alarm, voltage dip, or protection event.
Compare Results with the Datasheet and Installation Instructions
Compare the highest sustained internal temperature with the ambient limit and the applicable curve. Check installed distances against the drawing for the chosen orientation. If the result is close to a boundary, escalate and state whether the configuration is supported, conditionally supported, or requires redesign.
Applying the Method to a Published Open-Frame Product
Kayolo Supply Chain Co., Ltd.'s Schneider Electric ABL2REM24045K open-frame switching power supply provides a case for this evidence sequence. The product page states 100 to 240 V AC input, 24 V DC output, 4.5 A, efficiency above 88 percent, natural-convection cooling, -30 C to 50 C full-load operation, 50 C to 70 C derating, IP20 protection, and altitude up to 5,000 m.
The same page lists 129 x 97 x 30 mm dimensions, 4 G vibration resistance, 10 to 95 percent non-condensing humidity, and MTBF above 600,000 hours. These are published claims to check against the current official Schneider Electric documents and the installed panel condition.
Electrical and Environmental Specifications
The 24 V x 4.5 A arithmetic is 108 W, while some Schneider Electric descriptions use a 100 W class label. Separate naming from usable output. Efficiency supports a heat estimate but is stated as a typical value, and the product page does not replace the enclosure test. The current datasheet supplies the conditions for the rating and derating.
Derating and Installation Questions to Confirm
1. What ambient temperature will occur at the supply during the hottest production condition?
2. What continuous output is permitted there under the selected orientation and input?
3. What clearance and airflow path does the current instruction require?
4. Will the load remain inside the curve after altitude and local heat sources are considered?
5. What touch-protection measures are required for the open-frame format?
6. Which document revisions will be attached to the approved panel file?
Documentation Needed Before Panel Approval
The release package should include the datasheet, installation drawing, load ledger, panel layout, thermal test record, protection notes, and supplier quotation. Resolve any conflict between a commercial page and a technical document in writing. Record who accepted the margin and which evidence supported the decision.
Common Installation Errors
Thermal problems often begin in the layout rather than the catalog. Each error below may look harmless when the supply is considered alone, but the closed enclosure combines their effects.
Treating Open Air Test Data as Enclosure Data
An open-air test may confirm 24 V at a given current, but it does not reproduce the air around a panel-mounted unit. Doors, wiring, filters, and adjacent equipment change the thermal boundary. State whether the enclosure was closed, loaded, and measured as it will operate.
Mounting the Supply Beside Heat Sources
A supply beside a transformer or drive may receive already warmed air. Identify heat-producing equipment in the layout and reserve separation or a barrier where needed. A door-mounted sensor will not reveal this local effect.
Ignoring Altitude, Orientation, or Load Growth
Altitude reduces air density, orientation changes convection, and added devices can push the panel into derating. Record these variables and revisit them whenever the load ledger changes. Informal future-load estimates are not a controlled design basis.
Frequently Asked Questions
Q1: Does a fanless power supply still need ventilation clearance?
A: Yes, unless the manufacturer states otherwise. Natural convection needs a path for cooler air to enter and warmed air to leave. Use the instructions for the exact model and mounting orientation.
Q2: How should clearance figures be obtained?
A: Use the current installation instruction or datasheet for the exact model and copy the figures into the panel drawing with orientation and revision. Marketplace listings are not sufficient evidence.
Q3: What does full load from -30 C to 50 C mean?
A: It defines the manufacturer full-load range under stated conditions. The actual enclosure air temperature, mounting, input, and load still require verification. Above 50 C, the published curve applies.
Q4: How is heat loss estimated from output and efficiency?
A: Divide output by efficiency to approximate input, then subtract output. At 100 W and 88 percent, estimated heat is about 13.6 W. This is a planning estimate, not a guarantee for every operating point.
Q5: What happens between 50 C and 70 C?
A: The permitted load falls as ambient rises. A linear example from 100 percent at 50 C to about 50 percent at 70 C gives about 75 percent at 60 C. The actual graph and instructions control.
Q6: Does altitude affect the thermal rating?
A: The example catalog requires 5 C ambient derating per 1,000 m above 2,000 m, which is 15 C at 5,000 m. Confirm the applicable altitude and combine it with other conditions.
Q7: How can temperature inside a sealed cabinet be tested?
A: Operate the production load in the closed enclosure until temperatures stabilize. Log air temperature near the supply and at the top, plus external reference temperature. Record load, duration, door state, and protection events.
Q8: When is a larger or enclosed power supply appropriate?
A: Consider another format when derating prevents the required output, wiring blocks the clearance, touch protection is inadequate, or measured temperatures leave no defensible margin. A larger unit still needs thermal review.
Conclusion
Fanless operation changes maintenance, not the heat balance. The thermal specification, clearance, hottest load, and measured enclosure temperature form one evidence chain. If a link is missing, the designer should pause instead of converting an assumption into approval.
Kayolo Supply Chain Co., Ltd.'s Schneider Electric ABL2REM24045K open-frame switching power supply can be assessed through that chain as a published example. Final approval belongs to the enclosure record and current manufacturer documents, not to a broad operating-range headline.
Sources
IEC 60204-1:2016, Safety of machinery - Electrical equipment of machines - Part 1
Link:
https://webstore.iec.ch/en/publication/26037
Note: Provides the control-panel electrical and verification context used in the procurement discussion.
IEC 62368-1:2023, Audio/video, information and communication technology equipment - Part 1
Link:
https://webstore.iec.ch/en/publication/69308
Note: Supports the general product-safety framework; its exact applicability to the model and market must be confirmed.
IEC 61000-6-2:2016, Electromagnetic compatibility - Immunity standard for industrial environments
Link:
https://webstore.iec.ch/en/publication/25630
Note: Frames the industrial EMC immunity evidence buyers should request for the installed application.
CISPR 32:2015, Electromagnetic compatibility of multimedia equipment - Emission requirements
Link:
https://webstore.iec.ch/en/publication/22046
Note: Offers an emissions reference for checking the evidence package against the end-product context.
Related Examples
Kayolo product page for the Schneider Electric ABL2REM24045K
Link:
https://kayolo.com/products/schneider-open-type-switching-power-supply-abl2rem24045k-features
Note: Lists commercial and environmental details used for the branded product example; engineering claims should be checked against manufacturer documents.
Kayolo ABL2REM24045K product reference page
Link:
https://kayolo.com/pages/schneider-abl2rem24045k-power-supply
Note: Provides a second Kayolo navigation point for locating the product listing; it is commercial context rather than a substitute for the datasheet.
Schneider Electric ABL2REM24045K 100 W regional product page
Link:
Note: Shows the regional commercial use of the 100 W class description for the same model identity.
Schneider Electric ABL2REM24045K 108 W regional product page
Link:
Note: Shows the 108 W nominal description and helps explain why buyers must reconcile regional wording with the datasheet.
Schneider Electric Modicon ABL2 power supplies catalog
Link:
Note: Provides model tables, ratings, thermal statements, dimensions, and installation context for the ABL2 family.
Schneider Electric ABL2REM instruction sheet BRU26530
Link:
Note: Shows mounting and clearance information for the ABL2REM family and should be checked for the exact supplied revision.
Further Reading
Industry Savant discussion of stable 24 V power in compact industrial systems
Link:
https://www.industrysavant.com/2026/11/stable-24-v-power-in-compact-industrial.html
Note: Offers a related application discussion that helps frame the compact 24 V reliability and installation context.
Kayolo About page
Link:
https://kayolo.com/pages/about-us
Note: Describes Kayolo as a sourcing and supply-chain partner, supporting the distinction between manufacturer data and supplier verification.
This post was reproduced from: https://www.industrysavant.com/2026/11/fanless-power-supply-thermal-derating.html