DS-JAN23-PG08+09_Layout 1 05/01/2023 15:01 Page 2
COVER STORY ADVERTISEMENT FEATURE reserves under the prevailing conditions.
Derating at altituDe Derating is also necessary at an installation altitude above 2,000m. With increasing altitude, the atmospheric pressure decreases, meaning that the air density decreases, which also reduces the cooling effect of the convection air flow. Accordingly, the output power must
be reduced above 2,000m by a certain percentage per 1,000m or the ambient temperature must be lowered. The specified values for the necessary power derating vary depending on the power supply unit and can be found in every data sheet in the ‘Environment’ section. As an alternative to the power
reduction, a cooling system could be integrated in the control cabinet, which means that derating can be avoided.
Derating at alternative mounting orientations
If is required to mount the power supply in an orientation that deviates from the recommended standard installation, derating or limiting the ambient temperature is also necessary. The reason is the functionality of convection-cooled power supplies. The air flow inside the device cools the temperature- sensitive components, such as electrolytic capacitors, and the warm air is discharged to the outside. The recommended standard installation position is based on a ‘chimney effect’. The cool air enters the power supply at the lower ventilation grille, heats up due to the power losses of certain components, and is discharged again on the top of the device. In the development phase the devices are
designed according to cool design principles. Temperature-sensitive components that determine the lifetime are placed in the cool spots in the power supply. The developers position other components (for example, transformers) that heat up most at the top of the power supply so that they do not heat up the other components. In addition, PULS designers make sure that the air can always flow freely and is not blocked by components. If the device is mounted upside down or
on a table-top, for example, this affects the air flow. Without reducing the output power, the components could overheat, which has a negative impact on the lifetime and, in the worst case, can lead to a failure of the power supply.
FinDing the inFormation
Derating is necessary for almost all industrial power supplies above a certain temperature, installation altitude or in a deviating mounting orientation. PULS provides the necessary information for derating on the front page of its data sheets, enabling system developers and technicians to see this important information at first glance and adapt the power supply perfectly to the ambient conditions during installation.
PULS Power
www.pulspower.com
Derating for the table-top mounting of the CP20.241 (24V, 20A) DECEMBER/JANUARY 2023 DESIGN SOLUTIONS 9 Derating for the standard orientation of the CP20.241 (24V, 20A)
Derating for an upside-down orientation of the CP20.241 (24V, 20A)
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