Choosing a Power Supply: Efficiency and IP Rating Explained
Efficiency, power dissipation and IP rating decide whether a power supply runs reliably inside a sealed enclosure or a damp environment. This guide shows how to calculate waste heat, choose the right IP code and size in sensible reserves.
View power suppliesWhat does efficiency mean and how much heat appears?
Efficiency η is the share of input power that reaches the output as usable power. Modern switch-mode supplies reach 89 to 94 %, and the remainder turns into heat inside the unit. That waste heat must leave the installation space, otherwise the internal temperature rises and the life of the electrolytic capacitors falls.
Calculate the dissipation with PV = Pout · (1/η - 1). A supply delivering 240 W at η = 0.92 produces around 21 W of waste heat. At η = 0.85 it would be 42 W - twice the heat in the same housing.
Which IP rating suits enclosed or damp installations?
The IP code under IEC 60529 uses two digits: the first for protection against solid objects and contact, the second for protection against water. IP20 is touch-safe but open and unsuitable for moisture. IP65 is dust-tight and jet-proof, while IP67 withstands temporary immersion.
- IP20: open housing for a dry cabinet, with good heat transfer to the surroundings.
- IP54: protection against harmful dust and splashing water, for dusty workshops.
- IP65/IP66: dust-tight and jet-proof, for damp or washed-down areas.
- IP67: dust-tight and protected against temporary immersion, for outdoor and wet zones.
How do you size reserve and cooling correctly?
Power supplies should not run permanently at their limit. Plan a reserve and operate the unit at about 70 to 80 % of rated power. That lowers the internal temperature, keeps efficiency in a favourable range and clearly extends service life.
Mind the derating: above an ambient temperature of usually 45 to 50 °C the manufacturer reduces the permitted output. In a sealed housing the heat of every component adds up, so the internal temperature counts, not the room temperature.
Frequently asked questions
How do I calculate a power supply's dissipation?
Use P_V = P_out · (1/η - 1). At 240 W output and η = 0.92 you get roughly 21 W of waste heat that must be removed from the installation space.
What does the second digit of the IP code mean?
It describes water protection under IEC 60529. 5 means water jets, 6 strong jets and 7 temporary immersion. The first digit covers dust and contact protection.
Why does high efficiency matter in a sealed housing?
Because the waste heat stays inside. A higher efficiency generates less heat, keeps the internal temperature low and protects components from premature ageing.
Can I load an IP67 supply fully all the time?
Usually not. Potted IP67 units release heat only through the housing wall. Run them with a reserve and follow the manufacturer's derating curve.
Looking for the right supply for your installation?
We supply high-efficiency switch-mode power supplies with tested IP ratings from IP20 to IP67 - including advice on thermal sizing.
High efficiency
Switch-mode supplies at 89 to 94 % for low waste heat.
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IP classes to IEC 60529 from IP20 to IP67.
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Advice on derating and cooling inside the housing.
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