Managing the cooler (thermal control of fans in practice)
For those who use a computer every day (and especially every night), the idea of Silent PC is very close to its heart. Many publications are devoted to this topic, but today the problem of noise produced by a computer is far from being solved. One of the main sources of noise in a computer is the processor cooler.
When using software cooling tools such as CpuIdle, Waterfall and others, or when working in the Windows NT/2000/XP and Windows 98SE operating systems, the average processor temperature in Idle mode decreases significantly. However, the cooler fan does not know this and continues to work at full capacity with maximum noise level. Of course, there are special utilities (SpeedFan, for example) that can control fan speed. However, such programs do not work on all motherboards. But even if they do work, it can be said that they are not very smart. Thus, when the computer is booting, even with a relatively cold processor, the fan operates at its maximum speed.
The way out of the situation is actually simple: to control the speed of the fan impeller, you can build an analog regulator with a separate temperature sensor attached to the cooler radiator. Generally speaking, there are countless circuit solutions for such thermostats. But the two simplest thermal control schemes deserve our attention, which we will now deal with.
Description
If the cooler does not have a tachometer output (or this output is simply not used), you can build the simplest circuit that contains a minimum number of parts (Fig. 1).
Rice. 1. Schematic diagram of the first version of the thermostat
Since the days of the “fours”, a regulator assembled according to this scheme has been used. It is built on the basis of the LM311 comparator microcircuit (the domestic analogue is KR554CA3). Despite the fact that a comparator is used, the regulator provides linear rather than switching regulation. A reasonable question may arise: “How did it happen that a comparator is used for linear regulation, and not an operational amplifier?” Well, there are several reasons for this. Firstly, this comparator has a relatively powerful open-collector output, which allows you to connect a fan to it without additional transistors. Secondly, due to the fact that the input stage is built on pnp transistors, which are connected in a circuit with a common collector, even with a unipolar supply it is possible to work with low input voltages, located almost at ground potential. So, when using a diode as a temperature sensor, you need to operate at input potentials of only 0.7 V, which most operational amplifiers do not allow. Thirdly, any comparator can be covered by negative feedback, then it will work the way operational amplifiers work (by the way, this is exactly the connection that was used).
Diodes are often used as temperature sensors. For a silicon diode, the p-n junction has a voltage temperature coefficient of approximately -2.3 mV/°C, and a forward voltage drop of about 0.7 V. Most diodes have a housing that is completely unsuitable for mounting them on a radiator. At the same time, some transistors are specially adapted for this. One of these are domestic transistors KT814 and KT815. If such a transistor is screwed to a radiator, the collector of the transistor will be electrically connected to it. To avoid trouble, in the circuit where this transistor is used, the collector must be grounded. Based on this, our temperature sensor needs a pnp transistor, for example, KT814.
You can, of course, simply use one of the transistor junctions as a diode. But here we can be smart and do something more cunning :) The fact is that the temperature coefficient of the diode is relatively low, and measuring small voltage changes is quite difficult. Here noise, interference, and instability of the supply voltage interfere. Therefore, in order to increase the temperature coefficient of a temperature sensor, a chain of diodes connected in series is often used. For such a chain, the temperature coefficient and forward voltage drop increase in proportion to the number of connected diodes. But we don’t have a diode, but a whole transistor! Indeed, by adding just two resistors, you can build a two-terminal network on a transistor, the behavior of which will be equivalent to the behavior of a chain of diodes. This is what is done in the described thermostat.
The temperature coefficient of such a sensor is determined by the ratio of resistors R2 and R3 and is equal to T cvd *(R3/R2+1), where T cvd is the temperature coefficient of one p-n junction. It is impossible to increase the resistor ratio indefinitely, since along with the temperature coefficient the forward voltage drop also increases, which can easily reach the supply voltage, and then the circuit will no longer work. In the described regulator, the temperature coefficient is selected to be approximately -20 mV/°C, while the forward voltage drop is about 6 V.
The temperature sensor VT1R2R3 is included in the measuring bridge, which is formed by resistors R1, R4, R5, R6. The bridge is powered by a parametric voltage stabilizer VD1R7. The need to use a stabilizer is due to the fact that the +12 V supply voltage inside the computer is quite unstable (in a switching power supply, only group stabilization of the output levels +5 V and +12 V is carried out).
The unbalance voltage of the measuring bridge is applied to the inputs of the comparator, which is used in linear mode due to the action of negative feedback. Trimmer resistor R5 allows you to shift the adjustment characteristic, and changing the value of feedback resistor R8 allows you to change its slope. Capacities C1 and C2 ensure the stability of the regulator.
The regulator is mounted on a breadboard, which is a piece of one-sided foil fiberglass (Fig. 2).
Rice. 2. Installation diagram of the first version of the thermostat
To reduce the size of the board, it is advisable to use SMD elements. Although, in principle, you can get by with ordinary elements. The board is secured to the cooler radiator using a screw securing the transistor VT1. To do this, you should make a hole in the radiator, in which it is advisable to cut an M3 thread. As a last resort, you can use a screw and nut. When choosing a place on the radiator to secure the board, you need to take care of the accessibility of the trimming resistor when the radiator is inside the computer. In this way, you can attach the board only to radiators of a “classical” design, but attaching it to cylindrical radiators (for example, like Orbs) can cause problems. Only the temperature sensor transistor should have good thermal contact with the radiator. Therefore, if the entire board does not fit on the radiator, you can limit yourself to installing one transistor on it, which in this case is connected to the board using wires. The board itself can be placed in any convenient place. It is not difficult to attach the transistor to the radiator; you can even simply insert it between the fins, ensuring thermal contact using heat-conducting paste. Another method of fastening is to use glue with good thermal conductivity.
When installing a temperature sensor transistor on a radiator, the latter is connected to ground. But in practice this does not cause any particular difficulties, at least in systems with Celeron and PentiumIII processors (the part of their crystal in contact with the heatsink has no electrical conductivity).
Electrically, the board is connected to the fan wires. If desired, you can even install connectors so as not to cut the wires. A correctly assembled circuit requires practically no adjustment: you only need to use trimming resistor R5 to set the required fan impeller rotation speed corresponding to the current temperature. In practice, each specific fan has a minimum supply voltage at which the impeller begins to rotate. By adjusting the regulator, you can achieve fan rotation at the lowest possible speed at a radiator temperature, say, close to ambient. However, given that the thermal resistance of different heat sinks varies greatly, adjustments to the control slope may be necessary. The slope of the characteristic is set by the value of resistor R8. The resistor value can range from 100 K to 1 M. The higher this value, the lower the radiator temperature the fan will reach maximum speed. In practice, very often the processor load is only a few percent. This is observed, for example, when working in text editors. When using a software cooler at such moments, the fan can operate at significantly reduced speed. This is exactly what the regulator should provide. However, as the processor load increases, its temperature rises, and the regulator must gradually increase the fan supply voltage to the maximum, preventing the processor from overheating. The radiator temperature when full fan speed is reached should not be very high. It is difficult to give specific recommendations, but at least this temperature should “lag” by 5 - 10 degrees from the critical temperature, when the stability of the system is already compromised.
Yes, one more thing. It is advisable to first turn on the circuit from some external power source. Otherwise, if there is a short circuit in the circuit, connecting the circuit to the motherboard connector may damage it.
Now the second version of the scheme. If the fan is equipped with a tachometer, then it is no longer possible to connect the control transistor to the ground wire of the fan. Therefore, the internal comparator transistor is not suitable here. In this case, an additional transistor is required, which will regulate the +12 V fan circuit. In principle, it was possible to simply slightly modify the circuit on the comparator, but for variety, a circuit assembled with transistors was made, which turned out to be even smaller in volume (Fig. 3).
Rice. 3. Schematic diagram of the second version of the thermostat
Since the entire board placed on the radiator heats up, it is quite difficult to predict the behavior of the transistor circuit. Therefore, preliminary modeling of the circuit using the PSpice package was required. The simulation result is shown in Fig. 4.
Rice. 4. Result of circuit simulation in PSpice package
As can be seen from the figure, the fan supply voltage increases linearly from 4 V at 25°C to 12 V at 58°C. This behavior of the controller, in general, meets our requirements, and at this point the modeling stage was completed.
The schematic diagrams of these two thermostat options have much in common. In particular, the temperature sensor and the measuring bridge are completely identical. The only difference is the bridge imbalance voltage amplifier. In the second option, this voltage is supplied to the cascade on transistor VT2. The base of the transistor is the inverting input of the amplifier, and the emitter is the non-inverting input. Next, the signal goes to the second amplifier stage on transistor VT3, then to the output stage on transistor VT4. The purpose of the containers is the same as in the first option. Well, the wiring diagram of the regulator is shown in Fig. 5.
Rice. 5. Installation diagram of the second version of the thermostat
The design is similar to the first option, except that the board is slightly smaller. The circuit can use ordinary (non-SMD) elements, and any low-power transistors, since the current consumed by fans usually does not exceed 100 mA. I note that this circuit can also be used to control fans with a large current consumption, but in this case the VT4 transistor must be replaced with a more powerful one. As for the tachometer output, the TG tachogenerator signal directly passes through the regulator board and goes to the motherboard connector. The method for setting up the second version of the regulator is no different from the method given for the first option. Only in this option, the adjustment is made using trimming resistor R7, and the slope of the characteristic is set by the value of resistor R12.
conclusions
Practical use of the thermostat (together with software cooling tools) has shown its high efficiency in terms of reducing the noise produced by the cooler. However, the cooler itself must be quite efficient. For example, in a system with a Celeron566 processor operating at 850 MHz, the box cooler no longer provided sufficient cooling efficiency, so even with an average processor load, the regulator raised the cooler supply voltage to the maximum value. The situation was corrected after replacing the fan with a more efficient one, with an increased blade diameter. Now the fan reaches full speed only when the processor is running for a long time at almost 100% load.
Fan or cooler. A mechanical device with blades designed for forced airflow of various devices for the purpose of cooling them.
2005
The main goal of all computer fan speed controllers is to reduce fan noise. The fan rotation speed depends primarily on the level of voltage supplied to it. The lower the applied voltage level, the lower the speed and vice versa.
2006
Sitting at the computer at night, I noticed the excessive noise made by the air cooling system. Why not automatically, depending on the temperature, control the speed of the coolers? After 2 months, during which I searched for a suitable scheme, I improved and configured it. The circuit performs relay control of the speed of 3 coolers at once, depending on the temperature.
2006
In the proposed unit, the voltage supplying the motors is regulated by a pulse method! Field-effect transistors with very low (fractions of an ohm) channel resistance in the open state are used as switching elements. They do not limit starting currents and practically do not reduce the supply voltage for fans running at full power.
2010
This device is based on the PIC18F25K20 controller, which allows you to adjust the fan speed using PWM (pulse width modulation). This provides such advantages as: smooth adjustment of engine speed, low noise level, high durability, greater reliability, lower energy consumption and starting current.
2008
The principle of controlling the UMZCH forced cooling fan with a small heat sink is that the blower is turned on when the signal level at the amplifier output is exceeded a certain level, so the fan noise at reduced power is practically inaudible. A device with a fan can also be recommended for installation in amplifiers of a conventional design (with natural convective cooling) located in difficult operating conditions
The main problem with fans that cool this or that part of the computer is increased noise level. Basic electronics and available materials will help us solve this problem on our own. This article provides a connection diagram for adjusting fan speed and photographs of what a homemade rotation speed controller looks like.
It should be noted that the number of revolutions primarily depends on the level of voltage supplied to it. By reducing the applied voltage level, both noise and speed are reduced.
Connection diagram:
Here are the details we will need: one transistor and two resistors.
As for the transistor, take KT815 or KT817, you can also use the more powerful KT819.
The choice of transistor depends on the fan power. Mostly simple DC fans with a voltage of 12 Volts are used.
Resistors must be taken with the following parameters: the first is constant (1 kOhm), and the second is variable (from 1 kOhm to 5 kOhm) to adjust the fan speed.
Having an input voltage (12 Volts), the output voltage can be adjusted by rotating the sliding part of resistor R2. As a rule, at a voltage of 5 Volts or lower, the fan stops making noise.
When using a regulator with a powerful fan, I advise you to install the transistor on a small heat sink.
That's all, now you can assemble the fan speed controller with your own hands, without making any noise.
Best regards, Edgar.
The performance of a modern computer is achieved at a fairly high price - the power supply, processor, and video card often require intensive cooling. Specialized cooling systems are expensive, so several case fans and coolers (radiators with fans attached to them) are usually installed on a home computer.
The result is an effective and inexpensive, but often noisy cooling system. To reduce noise levels (while maintaining efficiency), a fan speed control system is needed. Various exotic cooling systems will not be considered. It is necessary to consider the most common air cooling systems.
To reduce fan noise without reducing cooling efficiency, it is advisable to adhere to the following principles:
- Large diameter fans work more efficiently than small ones.
- Maximum cooling efficiency is observed in coolers with heat pipes.
- Four-pin fans are preferred over three-pin fans.
There can only be two main reasons for excessive fan noise:
- Poor bearing lubrication. Eliminated by cleaning and new lubricant.
- The motor is spinning too fast. If it is possible to reduce this speed while maintaining an acceptable level of cooling intensity, then this should be done. The following discusses the most accessible and cheapest ways to control rotation speed.
Methods for controlling fan speed
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First method: switching the BIOS function that regulates fan operation
The functions Q-Fan control, Smart fan control, etc., supported by some motherboards, increase the fan speed when the load increases and decrease when it drops. You need to pay attention to the method of controlling the fan speed using the example of Q-Fan control. It is necessary to perform the following sequence of actions:
- Enter BIOS. Most often, to do this, you need to press the “Delete” key before booting the computer. If before booting at the bottom of the screen instead of “Press Del to enter Setup” you are prompted to press another key, do so.
- Open the “Power” section.
- Go to the line “Hardware Monitor”.
- Change the value of the CPU Q-Fan control and Chassis Q-Fan Control functions on the right side of the screen to “Enabled”.
- In the CPU and Chassis Fan Profile lines that appear, select one of three performance levels: enhanced (Perfomans), quiet (Silent) and optimal (Optimal).
- Press the F10 key to save the selected setting.
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Second method: fan speed control by switching method
Figure 1. Stress distribution on contacts.
For most fans, the nominal voltage is 12 V. As this voltage decreases, the number of revolutions per unit time decreases - the fan rotates more slowly and makes less noise. You can take advantage of this circumstance by switching the fan to several voltage ratings using an ordinary Molex connector.
The voltage distribution on the contacts of this connector is shown in Fig. 1a. It turns out that three different voltage values can be taken from it: 5 V, 7 V and 12 V.
To ensure this method of changing the fan speed you need:
- Open the case of the de-energized computer and remove the fan connector from its socket. It's easier to unsolder the wires going to the power supply fan from the board or just cut them out.
- Using a needle or awl, release the corresponding legs (most often the red wire is positive and the black wire is negative) from the connector.
- Connect the fan wires to the contacts of the Molex connector at the required voltage (see Fig. 1b).
An engine with a nominal rotation speed of 2000 rpm at a voltage of 7 V will produce 1300 rpm per minute, and at a voltage of 5 V - 900 rpm. An engine rated at 3500 rpm - 2200 and 1600 rpm, respectively.
Figure 2. Diagram of serial connection of two identical fans.
A special case of this method is the serial connection of two identical fans with three-pin connectors. They each carry half the operating voltage, and both spin slower and make less noise.
The diagram of such a connection is shown in Fig. 2. The left fan connector is connected to the motherboard as usual.
A jumper is installed on the right connector, which is fixed with electrical tape or tape.
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Third method: adjusting the fan speed by changing the supply current
To limit the fan rotation speed, you can connect permanent or variable resistors in series to its power supply circuit. The latter also allow you to smoothly change the rotation speed. When choosing such a design, you should not forget about its disadvantages:
- Resistors heat up, wasting electricity and contributing to the heating process of the entire structure.
- The characteristics of an electric motor in different modes can vary greatly; each of them requires resistors with different parameters.
- The power dissipation of the resistors must be large enough.
Figure 3. Electronic circuit for speed control.
It is more rational to use an electronic speed control circuit. Its simple version is shown in Fig. 3. This circuit is a stabilizer with the ability to adjust the output voltage. A voltage of 12 V is supplied to the input of the DA1 microcircuit (KR142EN5A). A signal from its own output is supplied to the 8-amplified output by transistor VT1. The level of this signal can be adjusted with variable resistor R2. It is better to use a tuning resistor as R1.
If the load current is no more than 0.2 A (one fan), the KR142EN5A microcircuit can be used without a heat sink. If it is present, the output current can reach a value of 3 A. It is advisable to include a small-capacity ceramic capacitor at the input of the circuit.
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Fourth method: adjusting the fan speed using rheobass
Reobas is an electronic device that allows you to smoothly change the voltage supplied to the fans.
As a result, the speed of their rotation smoothly changes. The easiest way is to purchase a ready-made reobass. Usually inserted into a 5.25" bay. There is perhaps only one drawback: the device is expensive.
The devices described in the previous section are actually reobass, allowing only manual control. In addition, if a resistor is used as a regulator, the engine may not start, since the amount of current at the moment of starting is limited. Ideally, a full-fledged reobass should provide:
- Uninterrupted engine starting.
- Rotor speed control not only manually, but also automatically. As the temperature of the cooled device increases, the rotation speed should increase and vice versa.
A relatively simple scheme that meets these conditions is shown in Fig. 4. Having the appropriate skills, it is possible to make it yourself.
The fan supply voltage is changed in pulse mode. Switching is carried out using powerful field-effect transistors, the resistance of the channels in the open state is close to zero. Therefore, starting the engines occurs without difficulty. The highest rotation speed will also not be limited.
The proposed scheme works like this: at the initial moment, the cooler that cools the processor operates at a minimum speed, and when heated to a certain maximum permissible temperature, it switches to the maximum cooling mode. When the processor temperature drops, the reobass again switches the cooler to minimum speed. The remaining fans support manually set mode.
Figure 4. Adjustment diagram using rheobass.
The basis of the unit that controls the operation of computer fans is the integrated timer DA3 and the field-effect transistor VT3. A pulse generator with a pulse repetition rate of 10-15 Hz is assembled on the basis of a timer. The duty cycle of these pulses can be changed using the tuning resistor R5, which is part of the timing RC chain R5-C2. Thanks to this, you can smoothly change the fan rotation speed while maintaining the required current value at the time of start-up.
Capacitor C6 smoothes the pulses, making the motor rotors rotate more softly without making clicks. These fans are connected to the XP2 output.
The basis of a similar processor cooler control unit is the DA2 microcircuit and the VT2 field-effect transistor. The only difference is that when voltage appears at the output of operational amplifier DA1, thanks to diodes VD5 and VD6, it is superimposed on the output voltage of timer DA2. As a result, VT2 opens completely and the cooler fan begins to rotate as quickly as possible.
Cooling fans are now found in many household appliances, be it computers, stereo systems, or home theaters. They do their job well, cool the heating elements, but at the same time they emit a heart-rending and very annoying noise. This is especially critical in stereo systems and home theaters, because fan noise can interfere with enjoying your favorite music. Manufacturers often save money and connect cooling fans directly to the power supply, which makes them always rotate at maximum speed, regardless of whether cooling is currently required or not. You can solve this problem quite simply - build in your own automatic cooler speed controller. It will monitor the temperature of the radiator and only turn on cooling if necessary, and if the temperature continues to rise, the regulator will increase the cooler speed up to the maximum. In addition to reducing noise, such a device will significantly increase the service life of the fan itself. It can also be used, for example, when creating homemade powerful amplifiers, power supplies or other electronic devices.
Scheme
The circuit is extremely simple, containing only two transistors, a couple of resistors and a thermistor, but nevertheless it works great. M1 in the diagram is a fan whose speed will be regulated. The circuit is designed to use standard 12-volt coolers. VT1 – low-power n-p-n transistor, for example, KT3102B, BC547B, KT315B. Here it is advisable to use transistors with a gain of 300 or more. VT2 is a powerful npn transistor; it is the one that switches the fan. You can use inexpensive domestic KT819, KT829, again it is advisable to choose a transistor with a high gain. R1 is a thermistor (also called a thermistor), a key link in the circuit. It changes its resistance depending on the temperature. Any NTC thermistor with a resistance of 10-200 kOhm, for example, the domestic MMT-4, is suitable here. The value of the tuning resistor R2 depends on the choice of thermistor; it should be 1.5 - 2 times larger. This resistor sets the threshold for turning on the fan.
Manufacturing of the regulator
The circuit can be easily assembled using surface mounting, or you can make a printed circuit board, which is what I did. To connect the power wires and the fan itself, terminal blocks are provided on the board, and the thermistor is output on a pair of wires and attached to the radiator. For greater thermal conductivity, you need to attach it using thermal paste. The board is made using the LUT method; below are several photographs of the process.
Download the board:
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After making the board, parts are soldered into it, as usual, first small, then large. It is worth paying attention to the pinout of the transistors in order to solder them correctly. After completing the assembly, the board must be washed from flux residues, the tracks must be ringed, and the installation must be ensured correctly.
