A power supply derating curve answers a conditional question: how much output is permitted under the conditions named on that curve? Two graphs on the same sheet are not automatically interchangeable. An input-voltage graph and an ambient-temperature graph can constrain the same application for different reasons.
This guide uses the source-controlled WEHO HDR-60-24 as the product reference. The specimen is marked 24V, 2.5A, corresponding to a 60W nominal output. That identifies the starting point. It does not establish that the full output is available at every input, temperature, orientation or enclosure condition.
Read the axes and notes before reading the curve
Start by identifying the exact model, document revision and meaning of each axis. A percentage of rated load is different from amperes; AC input voltage is different from cabinet temperature. Check which input, mounting orientation, airflow and output variant the graph assumes. A curve copied from a neighbouring HDR model is not a substitute for the ordered unit’s controlled sheet.
Record the footnotes as part of the selection evidence. The retained complete HDR-60 sheet does not provide the model-specific input/load and ambient-temperature/load curves needed for a numeric decision. This is missing evidence, not a small curve that has been decoded. Request those controlled curves from the manufacturer; do not borrow a neighbouring model’s graph. Public and retained operating descriptions also differ, so this draft gives a reading method, not numeric thermal breakpoints or a universal combined derating formula.
Keep the two checks separate
| Check | Question | Evidence needed |
|---|---|---|
| Input-related limit | What output is permitted at the actual supply input? | Controlled model-specific input/load curve and site conditions |
| Temperature-related limit | What output is permitted at the air temperature around the installed supply? | Controlled thermal curve, orientation and enclosure conditions |
| Combined operating point | How should simultaneous constraints be applied? | Manufacturer’s stated rule or application confirmation |
Do not multiply two percentages merely because there are two graphs. Do not automatically take the lower percentage either unless the manufacturer’s instructions support that method. If combined low-input and high-temperature operation is relevant, include both conditions in the technical enquiry and obtain a documented answer.
Use installed temperature rather than room temperature
A panel in a comfortable workshop may contain a warmer electrical compartment. Nearby contactors, drives and enclosure ventilation all affect the local environment. Define the relevant measurement location and test state with the equipment designer. A single outside-room reading is not proof that the internal thermal condition matches the graph.
Record whether the cabinet is closed, which neighbouring equipment operates and how long the selected state lasts. Use actual observed data only after testing. A generated application image must not display a fabricated instrument reading or be described as proof that a thermal test passed.
Keep body size and clearance distinct
The HDR-60 mechanical evidence identifies a 52.5mm horizontal width, 90mm upright height and 54.5mm body depth. A separate rear mounting projection is shown in the drawing; it is not a replacement for body depth. The source supports rear DIN-rail mounting, not an arbitrary front bracket.
Use the envelope to reserve physical space, then add the ordered unit’s required ventilation and service clearances. Filling every available gap with adjoining components can undermine the assumptions used for thermal selection. Do not infer a clearance from an illustration or use a ruler as a decorative substitute for engineering evidence.
Make the purchasing decision traceable
A useful release record contains the exact HDR-60-24 identity, controlled document revision, maximum load state, input condition, installed ambient and mounting arrangement. If a value remains unresolved, name it explicitly rather than borrowing a convenient limit from a catalogue summary. Preserve the original physical label unchanged in the accompanying product reference.
Is nominal 60W always available?
No. Nominal output and permitted output at a particular operating point are different decisions.
Can one curve cover both input and temperature?
Only if the manufacturer explicitly defines it that way. Separate axes and conditions need separate interpretation.
What should be sent with a technical enquiry?
The intended load, input extremes, measured or specified enclosure conditions and mounting layout. Ask how the exact revision handles their combination.
Official HDR-60 product reference. The original photograph and complete approved sheet accompany this local draft for revision-controlled review.
