7 tips for buying a fan

Keeping a cool head in selecting the right one The developer of electronic devices and equipment is now, more than a few years ago, confronted with the difficult task of heat dissipation. Although many components produce significantly less heat due to technological improvements, the devices power has risen by almost the same extent. The component density has especially increased, which makes effective and precise cooling more difficult. Careful cooling-management for components is more important than ever before. You can expect good cooling results if certain aspects are observed when buying fans.

1. Dimension the cooling generously. It is always possible to simplify an elaborate cooling arrangement, but under capacity cooling rarely succeeds. The capacity sometimes specified in the fan data sheets is for an air flow without back-pressure. Here, the data depicts the maximum air flow. However, if the fan blows in a closed space (without air leakage), it produces maximum pressure at zero air flow. This characteristic is also shown in the data sheets.

2. Dont be afraid of active cooling! The term ‘fan-less’ in the equipment description is often confused with maximum reliability. The electromechanical fan item is often classified as a risk component. However, a fan-less design is often bought with many disadvantages and more risk than a design that contains fan. The widespread poor quality of low cost fans leads to a high probability of failure. This risks the cooled devices with correspondingly high costs for the repair and for the resulting consequences. As a result, attempts are made to reduce the risk of problems by using designs without a fan. What is overlooked is that the low reliability of the fans results from the very low price that some suppliers use to gain a competitive advantage. It invariably follows that inadequate cooling of temperature sensitive devices results in increased risk of dramatic damage to components such as electrolytic capacitors.

3Cheap fans are expensive to use. Some failures with serious consequences could have been avoided by the use of good quality fans with ball bearings. Also, good fans are pre-aged (burnt-in), which makes early failures unlikely. Fans with solid bearings are not suitable for a wide temperature range, despite all the improvements with sinter bearing technology. Claims are made that fans with solid bearings are more resistant to shock. However, and especially at high temperatures they are likely to wear out more quickly even if the advertising promises something different.

4. Always use the largest possible fan to minimise noise level. Where appropriate, choose a reduced speed or use temperature to control the speed of the fan.

5. Ninety nine per cent of fan defects, especially with small fans, are caused by in-correct handling. Never touch the rotor, certainly do not distort it. Fans should not be stacked in store.

6. The mounting of the fan frame is important. Typically high-quality plastic is used. Nevertheless, it is possible due to incorrect, too high or too low, processing temperatures, during pressure moulding to get barely discernable faults. Such fans are easily deformed by hand and can change dimensionally during operation so that the fan blades touch. Fans from other, partially transparent plastics are not recommended. To make sure that the fan frame is not distorted, the assembly must always be attached to a flat surface.

7. Where DC voltage is not available AC fans are used. These fans are very expensive and require a disproportionate amount of unused power because of the regulations and insulation of the coils. AC fans with integrated AC/DC converters have a good efficiency, but they are also expensive and require additional space several centimetres deep. Moreover, the variety of types is limited. It is preferable to use an external AC/DC converter that can supply a standard DC fan. There is invariably a little space left somewhere in the device for small converters. If a standard fan can be used, there are many options, even for small and medium-sized quantities.