March 2, 2009, by kike_1974
Index:
- basic Parties
- Setting
- Rotor Motor
- fans Types
- Noise generated by fans
- dB fans vs
- A fan. more fans
- Recommended Fans
- fan bearings
Basic Parts of a fan
A computer fan consists of several parts: the motor, the motor control circuitry, the connector, the rotor (the blades ) and the fan frame. Here you can see the image of a fan removed:
can see that in the center of the frame fan motor is subjected. The rotor is attached to the fan motor through a bearing system, of which there may be several types. Namely the figure corresponds to a spherical cap or sleeve bearing. " Rolling
The major types of bearings that can be found are:
- cap bearing (sleeve bearing) : One of the most frequently used bearing due to its low manufacturing cost, is the use of two suitably lubricated surfaces. This type of bearing is one of the quietest, but it is short-lived compared with others. The lubricant can be dried or surfaces can be deformed, and this degradation is accelerated in the presence of high operating temperatures. To deteriorate the fan noise increases. A fan of this kind has a life span of 30,000 hours at 50 º C. Fans are generally more suitable for a SilentPC, with the disadvantage that need to be replaced after a few years (2-5, depending on usage). They are also sensitive to horizontal operation, which can decrease performance. Examples of fans with this kind are Bearing Silent Case Fan Nexus and Scythe Slip Stream
- ball bearing (ball bearing) : One of the most frequently used bearing in older fans, or many of the fans who are in power. The bearing consists of a row of balls. We can find fans with two ball bearings (ball bearing double or dual ball bearing "). They are more expensive to manufacture, but are more durable and resistant to temperature, and have no problems running horizontally. The drawback is that they are much more noisy than the previous. The average lifetime is around 70,000 hours at 50 ° C. Examples of this type of bearing can be found in fans of the series Enermax UC-FAB.
- bearing fluid ("fluid bearing ") : This type of bearing, which is usually much more expensive to manufacture, has a similar function to the bearing cap, but instead of simply being lubricated materials, add an area with oil (or other fluid) to pressure that "self-stabilizing" the axis of the rotor. This kind of fans are very durable, with up to 150,000 hours life span. They are not as quiet as the cap, but still quite quiet. As bearing fans ball are not sensitive to horizontal operation. Examples of these fans are Scythe S-Flex (with the system S-FDB bearing, "Sony Fluid Dynamic Bearing") and the Noctua (with the system SSO bearing, "Self Stabilising Oil").
fan Marco
The framework is the element that serves as the subject of the fan. The engine is held in the center of the frame and the framework provides the anchoring system (usually with screws) required to locate the fan. Additionally, the framework serves to indicate the direction of movement of the fan blades and the direction of movement of air through the fan. This information is usually indicated by arrows on the frame and, normally, the fan blows towards the place where the arms of the fan frame:
The frame usually has 4 holes in corners for bolting to the computer (actually 8, because it is on both sides, as seen in the fan picture above), or to serve as anchors for fastening sinks. Sometimes the frame is closed and the corners can be a problem because it takes longer screws or make it incompatible with the installation on some systems. This happens for example with Nexus fans:
In this case can be solved by cutting corners, as suggested in that thread SilentPCReview forum (which belongs above photo). Rotor
There are many designs of rotors. They can be classified into two main groups: Fans
- Radio: This type of fan blades are usually flat and shaped spokes, allowing the air flow is perpendicular to the axis of the fan. An example of radial fan:
Such fans are commonly used in graphics, chipsets heatsink motherboard, fan "blower" PCI slots. To generate a decent flow of air needed to operate at very high speeds, so they tend to generate enough noise, and are not suitable for a silent PC. For this reason we will not talk more about this type of fans. There are alternatives to these fans, for example, graphics cards can find many refrigeration systems that do not use radial fans (including no passive) or we can make any changes to use an axial fan , motherboards can use solutions passive (no fan more efficient heatsinks) or a "blower" PCI slots can be built an axial fan. Axial - : This type of fans move air in a direction parallel to the axis of the fan (or perpendicular to the frame, depending on how you want to see.) They are much more appropriate for a silent PC, you can build in many different sizes and there are many different rotor designs with different number, size and shape of the blades. Some examples:
As a curiosity, fans displayed in this picture are all 12cm, and are the models (from left to right, top to bottom): Scythe Slip Stream, Noctua NF-P12 Nexus Real Silent Case Fan, S-Flex Scythe, Noctua NF-S12 and Tacens Ventus. Motor
In the next picture you can see how is a motor of a fan, which is basically an electromagnet:
Opposite electromagnet usually control circuitry, which can be very simple as in the example on the left of the image below, or quite complex and can sometimes even contain a complete microcontroller:
A basic outline of the control circuitry is a scheme similar to one of these:
can see that in either There are two important elements: the solenoid (on the right side, "coils") and a Hall sensor (On the left, "Hall Sensor"). The magnet is the engine itself, which can be seen in the photos above. The Hall sensor is a circuit that detects the speed fan
The left diagram corresponds to a 3-pin fan (GND, + V, TACH) , where GND and VCC are inputs to this circuit, and TACH output is:
- GND is the reference or circuit ground,
- + V is food that nourishes both the Hall sensor and the fan coil and TACH
- is the sensor Fan speed (calculated value block Hall sensor).
The right scheme corresponds to a more advanced fan 4-pin PWM control (GND, + V, TACH, Drive) , which GND, VCC and Drive are inputs, and TACH output is:
- GND is the reference or circuit ground.
- + V is food, which in this case feeds the Hall sensor, and also serves to power the electromagnet
- is TACH fan speed sensor (value calculated by the Hall sensor block), just as in the previous scheme.
- Drive is a control signal, usually a PWM signal, which combined with food that provides + V, provides power to the fan coil.
can see that the simplest way to combine, in the diagram on the right, + V and Drive is via a simple transistor, such as N-channel JFET the figure, which functions as a switch: when you drive is high (12V) blocks the passage of + V, and when drive is low (0V) then allows the passage of + V. That is, the entry drive that is connected to control exactly when and when not + V to the electromagnet.
Of course, this is a basic outline, which can be enhanced with additional circuitry to improve detection velocity from the Hall sensor or PWM signal to reduce or even turn it into a constant voltage, or the inclusion of different elements of protection, etc. Depending on what each manufacturer wants to add circuitry can get fans of varying quality. There are other schemes
fans than these two that have been shown as an example. For example, sources Enermax modu82 + and PRO82 + use a scheme similar to the four pins on the right scheme, but use a "dual voltage." Instead of the + V input and drive to connect to 12V and a PWM signal, have two entries + + V1 and V2 connecting two levels different voltage, +12 V and a different one. The 12V is connected to the Hall IC, while the second is connected directly to the electromagnet, eliminating the need to attenuate the PWM signal. This system is one reason why these sources are the most popular sources quietest fan.
fans Types:
fans can be classified in many ways according to different characteristics such as flow direction (which we have seen before), size, connectors and circuitry, etc. Here are some of the different types of fans we can find. Size
There are many different sizes of fans (in mm, width x length x depth): 80x80x25, 80x80x38 92x92x25, 120x120x25, 120x128x38, 140x140x25, etc.
In general, a larger fan moves more air at equal speed (revolutions per minute or "rpm") to a smaller one. This means that to move the same amount of air the biggest fan needs to spin at lower speeds, which usually means less noise
However, a larger fan motor also needs a larger and generally more noisy. For this reason we look for an optimal size. Currently, the motors used in fans, the optimal size is 120x120mm. There are many silent fans on the market in these sizes (Scythe, Nexus, Noctua, Papst, etc.), While they are much harder to find in other sizes. For this reason, in choosing such a box for our computer, it is interesting to find one that has holes for 12cm fans, as they are the most likely offer us to build a silent PC. Vs PWM
. Voltage
As seen above, the fan motor circuitry has internal. This circuitry can be used to adjust the fan speed. There are two fundamental ways to regulate this speed:
- Voltage: You can vary the fan speed by decreasing the input voltage to the electromagnet. A lower voltage electromagmético generate a field of less force and cause the engine turn more slowly. This is the easiest way to control fan speed.
- PWM: You can adjust the speed of a fan attached to the electromagnet voltage pulses rather than a constant voltage. Voltage pulses conviernten in "pushing" the electromagnet, and reducing the time it is applying force on the electromagnet, effectively reducing the speed. These pulse signals are known as PWM signals (Pulse Width Modulation). PWM signal has two important features:
- Frequency: PWM signals used to control fans are usually periodic square wave of 12V, as the figure:
can see that the signal is repeated continuously. The time of each repetition (high over low signal) is known as the period of the signal. The inverse of this time is what is known as frequency and is measured in Hertz. For example, if the signal period is 50us. (Microseconds), then the corresponding frequency of that signal is 1/50ns = 20 KHz (kilohertz). The PWM signal frequency does not affect the speed of a fan, but can affect other aspects to be discussed later.
- duty cycle (duty cycle): The proportion of time the signal is high relative to the time that is low in each period is what is called a cycle. This is what really affects the fan speed. A PWM controller fan speed to really making speed variation is to vary the duty cycle.
More interesting information about the PWM control (and many more things related to fan control) can be found on this web , Cpemma (previous image of the PWM signal is taken from that site).
will see below the different types of fans depending on your plug, and see in which way these two modes of speed control to each of the types of fans.
Fan connectors
We have seen in the section relating to motor that there are two important elements Hall sensor and the electromagnet, and we have seen two different schemes, one with 3 inputs and one with 4 inputs. In addition we have seen two different forms of regular fans, by reducing the use of voltage or voltage pulses (PWM). These elements and features are going to differentiate the types of fans and connectors:
2-pin fans
These fans tend to ignore the Hall sensor and insufficient to enable the fan speed. The connector has only two pins, GND and VCC. It is common to see a connector molex "4-pin in this type of fans (of course with only two wires connected, for to GND and VCC:
can also see them with a standard as those that use 3-pin fans that we will see, but in this case with only two wires connected. Even be seen with other different connectors, in case of graphics cards or motherboard chipsets can carry smaller connectors (photo courtesy of Gnomo555).
can regulate the speed of these fans, contrary to what is sometimes mistakenly thought. These fans are the only thing that is a Hall sensor, so it is true is that although we can not regulate the fan know how fast it is spinning out of an extreme measure. The fan control can be done in two ways:
- varying the voltage that is connected to the VCC pin. Since VCC is connected directly to the coil, reducing the voltage also reduces the "strength" of the electromagnetic field that is generated for movel the electromagnet, and reduces the effective speed of the fan.
- Connecting a PWM signal on pin VCC. Also, being connected directly to the electromagnet VCC reduces the fan speed to get the voltage pulses.
3-pin fans These
fans do include the Hall sensor. The connector has three pins, GND, VCC and sensor, usually black, red and yellow, respectively, it may be different in some fans. VCC is connected at the same time the Hall sensor and magnet. The sensor pin is the output of Hall sensor that provides the fan speed.
The standard connector is as follows:
| P1 GND Black | |||
| P2 | Red+12 V, +5 V, or voltage source | ||
| Yellow | speed sensor (RPM) |
can regulate these fans are exactly the same way as that seen for 2-pin fans, ie varying the voltage on the VCC pin or by connecting a PWM signal on the same pin.
A problem with this type of fan to regulate any of these ways, is that not only varies the voltage connected to the electromagnet (either by downloading or by pulse), but also changes the input voltage circuits control (Hall sensor). This makes them work or at a higher voltage Low nominal (for voltage reduction), or on / off continuously (for PWM). This could reduce the life of the control circuits, especially in the case PWM high-frequency signals, but the truth is rarely a fan has been broken by these aspects.
The main problem is that, to avoid problems in the case regulated by PWM, would normally use a low frequency signal (precisely to avoid damaging the control circuitry), and if less than 20 kHz may be in hearing range human. In this case, we can hear sounds of "click" of the fan to the PWM signal frequency generated.
4-pin PWM fans
These fans also include the Hall sensor, but they have two different entries for feeding circuits and PWM control. As we have seen in speaking of motor in the schema of the circuitry 4-pin PWM fans, the Hall sensor (and other control circuitry) are continuously fed with 12V, and the electromagnet is controlled by the fourth pin, which connects a high frequency PWM signal.
The standard operation of these fans is specified in this document . The pin layout is as follows, although very few manufacturers continue the color scheme set the standard:
| P1 GND Black | |||
| P2 | Yellow +12 V | ||
| P3 Green | speed sensor (RPM) | ||
| P4 Blue | Control PWM (Pulse-width modulation) |
The main advantage of these fans on 3-pin is that all control circuitry is permanently running at nominal voltage. This allows you to connect a high frequency PWM signal to control the electromagnet, as in this case does not affect this frequency to the control circuitry. When connecting high frequency PWM signals in excess of the maximum frequency that we hear (usually higher than 20KHz), you get a quieter fan, noise-free "click."
also have the option of being independent control signal (PWM) signal power (+12 V) can even build dimmers to turn the entrance to the electromagnet in an intermediate voltage (no pulses), can get a smoother running engine (equivalent to the voltage regulation). This is optional, and do not think it's easy to see in the PWM ventilator on the market
In practice hard to find 4-pin PWM fans that are really quality. There are many more options to find quiet fans currently 3 pins.
connectors and regulatory boards
Some fans, called self-regulated , it comes with its own circuitry throttling temperature (including temperature-sensitive resistor which acts as a splitter and allows varying the voltage at the input fan). But more often is that the fans are regulated externally. The 3 types of fans we've seen from 2.3 to 4 pin usually connects to a motherboard or rehobuses containing mechanisms to regulate them (usually the plates using PWM, while we find rehobuses with either method, voltage or PWM). These regulators also tend to have connectors 2, 3 or 4 pins to connect the different fans. Let's see what kind of fans can be regulated in each of these connectors.
2-pin connectors:
connectors or simple fan controllers only need to use 2 pins to connect the GND and + V input of a fan (mass and connected to the electromagnet voltage). Do not use a third pin to monitor the fan rpm. An example of such a 2-pin connectors can be seen in the picture below (courtesy of Gnomo555):
simpler controller can be found is the molex connector from power because can provide direct voltages of 5V, 7V and 12V. The supply molex connector has 4 pins: 12V (yellow), GND (black), GND (black), 5V (red). Using the appropriate adapter, any fan of 2, 3 or 4 pins can be controlled by this form. The adapter simply plug properly appropriate voltages on the two pins of the fan. For example, connecting black and red wires from the source + V GND and 5V are achieved by connecting the black and yellow cables are getting 12V, and connect the red and yellow are getting 12V. These adapters can buy or make yourself , it is not complicated.
Besides this, you can find other regulators of two pins, either voltage or PWM, but usually they were used at least 3 pins, using the third pin speed sensor to report the fan rpm.
3-pin connectors
These are the most common connectors that can be found on motherboards and rehobuses. The third pin can be used by the board / rehobús to monitor fan speed. The other two (pin 1 and pin2) are common GND and + V to regulate fan of either of the two forms known, for voltage or PWM.
This connector can connect 3-pin fans obviously directly. As shown in the photo, the connector has a tab for that it is possible to connect the single way possible, and match the pins GND, + V and sensor of the fan and GND pins, + V and sensor plate.
You can also connect 4-pin fans (as before, the power connector tab is only possible to connect only one way). In this case, the fourth fan pin (PWM) will be on the air, being connected only GND, + V and sensor:
can regulate a 4-pin fan this way. If we recall how the circuitry for a 4-pin PWM fan, + V is connected to both the circuitry of the fan and the coil through a transistor. The transistor in this case will be constantly driving, so the fan behavior will be exactly that of a 3-pin fan (+ V is connected directly to both the circuitry and the electromagnet.
4-pin connectors
4-pin connectors are becoming more common on the plates basis of current computers. They have 4 pins that correspond to one of the following schemes:
- GND - 12V - sensor -
- PWM GND - + V - sensor - GND
The first scheme is designed to connect a 4 pin fan, being a perfect correspondence between pins. The board will generate a voltage of 12V in the second pin and cover the fan through a PWM signal
With this scheme, if we connect a 3-pin fan will operate at full speed (to be connected to 12V + V input of the fan. As in previous cases there is only one possible way to connect a 3 pin fan connector 4, due to the tab of the latter:
The second scheme is designed to connect 3-pin fans, and also regulate them. This second configuration is equivalent to running a board connector 3-pin as we have seen in the previous section.
normally plates using the first of the schemes for 4-pin fans, and fans can connect both 3 and 4 pins, but you can only regulate 4.
Some boards may have a connector that allows to select between the first and second schemes. Contain additional hardware (multiplexers to select pins 2 and 4 the relevant entry) and additional software in the BIOS to select an option and another. That is, we can select what type of fan we want regular, 3-pin or 4 pin. Usually this is usually (when) only the connectors CPU_FAN. " In the ASUS motherboards that have this option (for example, my Asus P5W DH Deluxe has one), we can see in the BIOS is an option called "Q-FAN CPU Mode" which we selected as "DC" for the second schema or "PWM" for the first scheme. Another example, Gigabyte boards have this option (my motherboard Gigabyte GA-P45-UD3R) is called in the BIOS as "CPU Smart Fan Mode", and the options are "Auto", "Voltage" or "PWM".
For motherboards, instead of the BIOS to configure the connectors, you can use any software to change settings. A software that can be used is the Speedfan program, which serves to automatically configure the way that the motherboard controls the fan. In This article is a guide Speedfan.
noise generated by fans
After learning the basic features of the fans, we finally get what we want, the noise produced by fans. The fan noise is usually generated by the following factors (listed in order of importance):
- Turbulence: The biggest noise produced by fan noise is due to turbulence and friction of the air moving. This noise is inevitable. Two factors mainly affect this kind of noise: the design of the fan rotor, which can help to generate less turbulence, and the amount / speed of air moving fan.
words, to avoid this kind of noise we find fans with an efficient design of the rotor, and also try to make them work at the slowest speed necessary ... for that we just talked about all the ways to regulate the speed of a fan.
Also consider the size of the fan. As discussed in the section concerning frames fans and size at the same speed the higher the fan moves more air it. With greater size, the same amount of air will be distributed in space, and therefore produce less noise from turbulence. That is, fans should look as large as possible from this point of view. Although, as also mentioned, there is a limit, because too large fans begin to influence other factors such as engine noise, and therefore we must find a balance. Currently this balance is the 120mm fans, as it is very hard to find 140mm silent fans and older. - Vibration: Another way to generate fan noise is vibration. A fan noise produced by vibrating itself, but if it is subject to another element, such as computer case, then can transmit these vibrations and amplify them.
There are fans that vibrate vibrate more and others less, but this type of noise can be eliminated almost entirely if you use rubber screws or other solution to "decouple" from the box or item to which they are subject. Thus, the rubber absorbs vibrations while not transmitted. - motor bearing and friction: The actual engine fan noise may occur either because the hardware makes noise, or by the friction of the fan bearings themselves.
The solution here is obviously trying to choose fans that have minimal engine noise. Choose sleeve bearing fans, for example, is to ensure a sound of this part of the fan
One factor that may affect the noise of a fan is pressure which is under. A fan running at idle is quieter than a fan who has to "make force" to move the same amount of air. So fans who are in boxes of computer very restrictive to airflow (with few openings, or disorganized cables and elements that obstruct the flow, or located in front of a filter or sink) will be more noisy and is a factor into account.
There are fans who behave much worse others at higher pressure. For example, the Noctua NF-S12 fans are fans with a serious problem with these kinds of conditions
Another factor influencing the objects found near a fan. A fan has a grating or a sink right in front, will produce more noise turbulence noise. No matter how well the fan is designed to create minimum turbulence possible, if we put an object before we totally change the operating conditions. DB
fans have already seen that produces noise in a fan. Usually the overall noise of the fan, as well as general noise of the different elements, measured in dBA. As we saw in this other article about silent PCs in general, must be very careful how to interpret the measures dBA SPL.
therefore do not recommend looking at measures to compare fans manufacturers, since each uses a different reference (measurement distance, background noise measurements, etc..). Measures to compare the best fans are those found in the reviews of different websites, since they use the same reference for all. My favorite for these comparisons is SilentPCReview . Perhaps in the future may find in "The Web of SilentPC" comparisons made by me ... :)
vs A fan. more fans
If you want a silent PC, and we clearly need large enough fans (to minimize turbulence noise) and are regulated at the lowest possible speed. They also have to be fans of quality motor with low noise and possible aser decoupled from the box or item to which they are subject with rubber to absorb vibrations and prevent its transmission.
The next question is: How many fans do we need?, And associated with this question also wonder whether to have many fans at low speed, or a few fans at a higher speed.
In general, the answer is that it is better to have more fans at low speed under high-speed fans. In fact, one can prove mathematically that the sum of two sounds exactly the same and fully synchronized in frequency increases the noise in 3dBA: if we assume two magnitudes noises R1 and R2 such that R1 = 2 * R2 (ie one is twice the other) and their corresponding values \u200b\u200bpassed to db, db (R1) and db (R2), we have:
db (R1) - db (R2) = 10 * log2 ~ 3dB
In practice, sound of two fans are not the same frequency will be offset each other, so the additional noise perceived by adding a fan is usually lower than those 3dBA. Furthermore, each fan add, generally adds less noise than before.
However, doubling the flow of air that a fan moves is usually a significant increase in speed and noise, generally more than double (ie, more than 3dBA).
Therefore, taking into account the above, it is worse to a single fan moving a certain amount of air that move put two each half. The sound of two fans combined is well below the other noise alone, moving in both situations the same amount of air. To verify this, we use a real example: Consider
a fan, for example a Scythe Slip Stream 1200. If you look at the data obtained by SilentPCReview this fan, we can look to for moving 24CFM have a 18dBA noise, and to move 46CFM (which does not even twice), the noise is 28dBA, up nothing less than 10dBA. We know that two of these fans move 24CFM air moving twice (actually even slightly more), and increased noise will be less than 3dBA.
Of course, we must find a balance between the number of fans to use and the speed of these, and that by adding a growing fan noise.
should also mention that in addition to these mathematical considerations using dBA, it must be said that what we perceive is not exactly what they say dBA. As discussed above, the DBA does not contain information on the frequency of the signal, and our ears and brain can interpret sounds differently with the same extent and apparently one dBA louder than another. The important thing is that the practice corroborates what we said in the previous analysis, and two fans make less noise than a single one, assuming that in both situations to move the same amount of air recommended
Fans:
In this article we have seen the basics of running fans, and what affect the noise they make. This is just the beginning, in a forthcoming article "Fans Recommended" will display a selection of the quietest fans, features, links to reviews and analysis, opinions, etc.. I hope that will soon be available, there is still much work to do on this website.
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