Switching power supplies, adapters, and DIN-rail units are sold by wattage. The load cares about voltage, continuous current, and what happens when the cabinet is hot and the mains dips. Those are the lines to put on the drawing.
Separate continuous current from marketing power
Multiply the voltages you need by the currents the boards and actuators actually draw, then add margin for inrush of relays and disk drives. A motor drive or a PCBA with a radio can pull a peak well above its average. Ask how long the peak is allowed. Ripple and noise matter for analog sensors; a dirty 24 V rail is a common reason a 4–20 mA reading wanders.
Heat and input range
Industrial cabinets are not 25°C. If the curve forces you to half the current at 60°C, the “compact” supply is the wrong one. Note whether cooling assumes free air or a fan, and do not block the vents with the cable duct. On the input, write the real mains: 100–240 V single phase is not the same purchase as 380–480 V three phase. Power factor correction is a compliance and a harmonic question on larger supplies, not a badge.
| Line on the drawing | Why it is there |
|---|---|
| Output voltage and set tolerance | 24 V nominal can be 23 or 28 V at the screw |
| Continuous and peak current | Stops a supply that only meets the number for seconds |
| Hold-up at full load | Says which sags the product will ignore |
| Isolation and the safety standard | Names the report instead of “CE power supply” |
A UPS or an inverter is a different product: it is there when the mains is gone, not when the 24 V rail needs to be clean. Battery choices for that job are in battery chemistries. For the AC motor itself, start with the drive guide rather than a larger adapter.
Questions buyers actually ask
Is a 150 W supply a 150 W supply at 60u00b0C?
Often no. Many open-frame supplies must be derated as ambient temperature rises, and some assume a minimum airflow. Read the derating curve and the mounting orientation, then size the supply for the current you need at that point.
What is hold-up time?
How long the output stays inside regulation after the AC input disappears. A few milliseconds covers a brief sag. It is not a UPS. If the machine must ride through real outages, that is a separate battery or UPS specification.
Are a wall adapter and an open-frame supply interchangeable?
Not as a drawing. An external adapter already has a case and a plug. An open-frame supply needs creepage, an earth strategy, and a fire enclosure provided by your product. Do not drop one into the otheru2019s approval and assume it still holds.