Power supplies with a convection rating and a higher fan-cooled rating are often overlooked when considering peak load applications but can be a safe and reliable choice for peak load applications. Such a supply could be rated at up to 50% higher power when fan-cooled, compared to a naturally or convection cooled environment.
Dual rated products are electrically rated for the higher power rating and thermally rated for the convection cooled power rating. This is ideal for peak load applications where the peak load does not exceed the fan-cooled rating and the average load is lower than the convection rating.
In general, the larger the difference between the fan-cooled, or peak, rating and the convection rating, the shorter the peak load capability. Dual rated products normally specify a list of key components and their temperature ratings, to ensure safe and reliable operation in end applications. Use this information to ensure that the product will not overheat in a peak load application by monitoring the temperature of the key parts within the end application during the development phase.
The specification also usually outlines lifetime expectations, based on key electrolytic capacitor temperatures. Use this information to confirm the suitability of the product for your system requirements.
You can select and specify a dual rated power supply for a peak load application based on readily available thermal data. For reliable and safe selection, check that the average power requirement does not exceed the continuous convection rating of the supply and that the peak load does not exceed the maximum power rating when fan-cooled.
The key parameters are:
Peak power required, which must not exceed the fan-cooled rating
The maximum duration of the peak
The duty cycle
The power consumed by the load during the non-peak duration
The average power drawn from the supply when the peak & normal running conditions are combined
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