40mm fans are a type of axial fan that is commonly used in CPU or server builds to cool down some of the heat-generating electronics. As CPUs or other electronics are in use, they generate a lot of heat that needs to be cooled or moved to prevent the heat from causing damage to the other components.
40mm fans are very small and thereby have a limit to how powerful they can be. That said, they are also very quiet and a preferred cooling option for builders. For protection and to easily fit inside build cabinets, 40mm fans are encased in a plastic shell that varies in depth.
The noise made by any fan is generated by how fast the blades are spinning. Traditionally, 40mm fans were considered noisy as they had to work at a high rpm in order to effectively cool their systems. Today, RS carries quiet 40mm fans that generate very little noise even at high speeds, like our 24v 40mm fans.
While it's good to know that fans are working, fan noise can often be a nuisance to work with, which is why many engineers seek quiet and silent 40mm fans.
Picking the right 40mm fan for your build depends on a few key factors. You need to know how much space you have to work with, or else the fan will not fit. A common size is 40x40x10mm, but you should measure the available space in your cabinet.
It is also important to understand how powerful you need the fan to be and how it will draw its power. Many 40mm fans draw power from DC currents, however, there are also many models that draw from AC currents. The strength of the fan can be measured by which voltage it's rated for, with higher voltages equating to more power.