Every degree counts: Schukat will help you find the right cooling solution.

With increasing efficiency, power supplies are getting smaller and smaller while at the same time providing an ever-increasing range of functions. Because the operational life of the installed components – especially the electrolytic capacitors – is heavily dependent on temperature, operating temperatures should, to the greatest possible extent, be kept below the maximum allowable temperatures. Good thermal design and suitable, effective heat dissipation are thus crucial to reliable operation.

Power supplies can be cooled in a variety of ways: pure convection cooling, forced-air cooling with fans, contact cooling, and water cooling. Depending on the process, a manufacturer-specified installation position may have to be observed. If this is not done, heat may be dissipated inadequately and can accumulate in the device despite seemingly adequate ambient temperatures.

At first glance, actively cooling a power supply using an integrated fan is the simplest variant. The fan is appropriately sized and properly positioned by the manufacturer. But even here, two important points need to be observed: first, the maximum permissible ambient temperature, and second, unobstructed air circulation through clear vents. In applications where higher levels of dust and dirt are expected, air filtration for fan cooling is indispensable, and the filter must be regularly exchanged or cleaned as necessary.

• Noise generated by rotational motion and airflow.

• Deposits on the fan opening / fan guards / filters: airflow may drop too low to cool sufficiently, which may trip the temperature monitoring or “kill” the unit through overheating.

• Heavy contamination can block the fan and cause the power supply to disconnect.

• Dust and moisture inside the power supply: if this happens, clearances and creepage distances cannot be sufficiently maintained, causing the dielectric strength to sink and possibly leading to sparking and damage to the product.

If a power supply or the entire application is enclosed in a case, the waste heat from the device can cause the temperature inside the case to exceed the allowable operating temperature. Then either derating according to the data sheet has to be taken into consideration or another cooling solution found, e.g. with a fan.
The airflow rate required for "forced ventilation" can be approximated theoretically based on the total energy converted to heat within the enclosure and the maximum allowable temperature rise. In practice, however, determining a suitable fan is not so straightforward. This is because the fan has to overcome a certain level of resistance in the system, which depends on various factors: the packing density and placement of components inside the case, airflow velocity, the size and position of intake/exhaust openings, and any filters in use. This is not always easy to determine, but by measuring the airflow or the actual temperatures at critical system components, a suitable fan or the right airflow can be determined empirically based on the values derived. Depending on the complexity of the application, a thermal simulation also makes sense for accurately assessing the right fan and its optimal positioning.

Open-frame industrial switching power supplies – i.e., supplies with no surrounding case – are often operated either at reduced power with only convection cooling or at nominal power with active cooling. For the (Fig. 2) EPP-500-24, a 24V open frame power supply from manufacturer MEAN WELL with a 5x3 inch footprint, the data sheet specifies a convection-cooled maximum power of 320W. If, however, you want to draw up to 500W of power from the unit, active cooling is necessary. In that case, you will need to consider the mounting position, maximum permissible ambient temperature, and the dimensioning and positioning of the fan. If the installation or fan positioning deviates from the data sheet, the maximum temperatures at the power supply's critical individual components must be taken into account. The corresponding specifications can be found in the manufacturer’s technical documentation.

Contact cooling is an elegant solution that sidesteps active fan cooling, dissipating a large proportion of the generated waste heat through a thermally optimized baseplate. The power supply and/or its baseplate are thermally coupled to, for example, a metal enclosure wall for heat dissipation.

Contact cooling can dissipate much of the heat, but free air convection often also contributes. A measurement reference point (T_case) on the power supply case indicates the maximum temperature that must not be exceeded during operation for a specific application. The use of such contact-cooled power supplies partially eliminates the need for ventilation openings, thus avoiding both the potential failure of the supply due to possible contamination as well as the noise generated by a fan.
In MEAN WELL’s UHP series (Fig. 3), the waste heat in the unit is optimally distributed through partial potting with a thermally conductive potting compound and conducted to the base plate, fully utilising its surface area. The series can also be purely convection cooled with derated performance, or the heat dissipated using an external fan.

Schukat electronic offers power supplies from MEAN WELL and other manufacturers. Schukat stocks around 6000 different types of power supplies and DC/DC converters in production quantities at its automated central warehouse in Monheim am Rhein, Germany.

As a distributor, we provide fast, competent support with direct contact persons in-house, and also have an expert field service team for on-site problem solving. Customers benefit from rapid processing of inquiries, availability of data sheets and samples, and variable delivery quantities – from samples to series production.

Our technical sales team is here to help when selecting suitable power supply products as well as for any customer-specific questions relating to thermal management.