MICROMASTER: Cooling requirements for inverters
How can I calculate the heat dissipation of an inverter?
The figures given for ambient temperature always refer to the temperature next to the inverter , i.e. inside the cubicle , if the unit is mounted within a cubicle.
- Operation in an unventilated cubicle
When units are mounted in an enclosed , unventilated cubicle , the internal temperature will rise due to heat losses from each of the units in the cubicle . This temperature rise can be estimated using the total power dissipated within the cubicle and the exposed surface area of the cubicle as follows :
Temperature Rise = Total Power Dissipated (W)/(5.5 x Exposed Surface of Cubicle(m2)
For example, if the total power dissipated in a cubicle is 300 W , and the exposed surface area of the cubicle ( typically roof, sides and front; note that the floor and back are not normally exposed ) is 4 m² , then the rise in temperature above the external ambient temperature, and solely due to the single inverter under consideration within the above cubicle, will be: 300/(5.5 x 4) = 13.6°C rise This temperature rise must be taken into account when rating the inverter and other equipment in the cubicle. Furthermore do not forget the effect of other heat sources within the cubicle which will further raise the internal temperature.
- Operation in a fan-cooled cubicle
If the cubicle is ventilated by a fan, then temperature rise within the cubicle can be calculated using the following formula: Temperature Rise = ( 0.053 x Total Power Dissipated(W) ) / Air Flow in the Cubicle(M3/min)
Once again do not forget other heat sources within the enclosure and remember that the fan volume should be derated to take account of air-low restrictions. The inverter must not be operated outside it’s temperature specification. This is the environment in which the inverter is operating. A suitable ambient air temperature outside the enclosure does not therefore guarantee a successful application.
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