The electric motors that are used in PC fans are known as “brushless direct current motors” or BLDC for its acronym in English, but within the fan motors there are different types, the 4-pole being the most frequent. However, there have been six-pole fans like those from be quiet !, for some time now, and the manufacturer says they are better than their lower-pole siblings. In this article we are going to tell you how this type of fan works and how it differs from the others.
In the past, motors had a metal brush at the end of their rails that touched the rotations of the motor that generated the energy. They worked well, but as they had constant friction there was a fairly high wear, as well as making a lot of noise and even producing sparks. Brushless motors have replaced these for quite some time, as they are much quieter and more reliable.
What is a six pole fan motor?
To understand what a six-pole fan is and how it differs from a four-pole fan, we must first know its structure: the outer casing is the rotor , which consists of four-pole integrated magnets, while the inner core called a stator , it incorporates several copper coils (usually four or six), hence they are called four or six-pole fans.
In a six-pole motor, the copper coils fill most of the available space inside, which improves efficiency as losses are significantly reduced.
Let’s explain it with an example: imagine a merry-go-round or carousel, in which four people are located in the four cardinal points: north, south, east and west. These people push the carousel every time it passes where they are, but between passing one and reaching the next, there is a period of time in which no one is pushing it and therefore there are losses of speed.
By adding two more people (for a total of six), the frequency with which someone is pushing the merry-go-round is increased by 50% , thus increasing efficiency much more since there is practically always someone pushing it and therefore does not lose hardly speed. This at the same time makes the rotation speed more homogeneous, since it hardly loses speed.
Something similar happens with a four or six pole fan rotor; As soon as direct current is conducted into the system, the copper coils become electrically charged , turning them into magnets. Due to the laws of physics, they begin to interact with the magnets in the rotor, and thanks to this parallel attraction and rejection the rotor turns. This is common in all fans, but the fact that there are six and not four coils means that energy losses are lower and that the speed of rotation of the fan is more homogeneous , reducing vibrations as well .
So is the better the more poles you have?
A reasonable doubt that may arise is that if a six-pole motor in a fan gives it greater homogeneity when turning, more stability and efficiency, why not put a greater number of coils then?
The answer is that there are obviously physical limitations. You cannot add more coils because you cannot make a rotor that is too big because otherwise there would be no space for the blades, which in the end are the ones that move the air; Another alternative would be to make the coils smaller, but in that case the magnet that is created by applying an electrical charge would not have enough power to make the system rotate.
However, as you can see in the image below, there are fans with more poles (in the image you have one with no less than 12 poles), but you can also see the obvious physical difference in terms of the size of the motor, much larger than the one used by conventional fans. A 6-pole fan can be integrated in the same space as a 4-pole without losses, which is why it is considered to be ideal.
On the other hand, adding more material would mean an increase in the manufacturing cost and production time, which would lead to a notable increase in the sale price of the fans. To this must be added that the number of coils must be a multiple of two, since a magnetic field inevitably requires two magnetic poles for it to work.
