Introduction

At first glance, you may think, "It's just a fan". Why complicate something so simple. After all, it's just another component to deal with and anything extra adds additional cost to the system. This statement may be true for most typical applications, but applications that are sensitive to noise and power, this option adds value.

Fan noise and power are directly related to the output performance of the fan. If additional CFM is needed, an increase in noise and power will also be the result. In this world there is no free lunch. But what if we can reduce the amount of CFM during times where system loads are minimal. During these moments, we can reduce the CFM and consequently lower the emitted noise and power requirements. If the load increases, we can increase the CFM to meet the cooling requirements. The result is a win-win situation for today's thermal cooling needs.

There are many ways to control the speed of a fan. Controlling the speed of the fan can be as simple as regulating the input voltage to the fan to using more complicated digital microprocessor inputs. These methods are further addressed below and we offer guidelines to follow when considering each option for your application.

Voltage Regulation

The voltage regulation option is designed for applications where the input power may fluctuate at different voltage levels. An example would be a backup generator, or outdoor telecommunications equipment that periodically undergoes battery regeneration. In these applications, a change in input voltage would result in a change in the fan's rpm and thus, noise and power.

To avoid unwanted fluctuations, Comair Rotron fans can be equipped with an internal regulating circuit that maintains a constant voltage source to the fan windings; regardless of how the input voltage changes. This is accomplished by using a voltage regulator and clamping the adjust leg with a zener diode. See Figure 1. Everything is built into the fan. There are no extra components or extra wires to deal with in your system. The Comair solution is simple and easy.

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