Circuit design PWM speed controllerDC motor.
The control unit for the electric fan of the "Borey" cooling system (BU EVSO) or the controller for the "Argest" stove, as a PWM speed controller, consists of:
- microprocessor(PWM signal generation, current and temperature measurement, mode indication);
- power transistor(current switching, actuator element of the PWM speed controller of the electric fan);
- filter (elimination of electromagnetic interference).
The rotation speed of the commutator motor can be adjusted by changing the voltage supplied to it. At a constant voltage value of the power source - the battery, the voltage on the engine can be changed by changing the resistance in the engine circuit, for example, using a rheostat or transistor. However, when controlling powerful drives, this method leads to the release of large thermal power at the resistance (transistor) and a decrease in system efficiency.
You can increase efficiency by applying full voltage to the motor, but for a limited time. If this is done with a high frequency, then by controlling the duration of switching on, you can actually change the average voltage supplied to the motor.
Changing the duration of pulses with a constant repetition period (constant frequency) is called pulse-width modulation ( PWM, in English texts: PWM-Pulse Width Modulation).
When controlling engine speed using pulse width modulation, full power supply is applied to the engine, but the time for which it is applied is controlled. Relatively speaking, the PWM fan speed controller closes the power switch every second for a tenth of a second, if we need 10% of the engine power, if we need 25% of the power, then the PWM speed controller closes the power switch for a quarter of a second, if 50% of the power - then half a second, etc. When we need to spin the engine to full power, the PWM speed controller closes the power switch for a full second, that is, in fact, the power switch does not open at all. 
Of course, in reality the microprocessor controls the power switch with a frequency much higher than once per second, but the principle remains the same. At a sufficiently high frequency, the current ripple in the inductive load is smoothed out, and some effective voltage is actually applied to the motor. Let's say, with a supply voltage of 12V and a pulse duration of 50% of the period, exactly the same result is obtained as when a voltage of 6V is applied to the motor.
When operating a car in the urban cycle with high ambient temperatures, when the probability of engine overheating is maximum (especially in traffic jams), the mode of smoothly changing the fan rotation speed within 30-60% using a PWM speed controller is sufficient to limit the temperature of the car engine. The use of the EVSO control unit in the car cooling system eliminates the need to turn on the fan at a power higher than 60% (especially at full power), thereby ensuring almost complete absence of noise in the car interior, in contrast to the annoying roar of an electric fan working at full capacity in a conventional system car engine cooling.
An engine cooling fan is a special device that provides airflow to the radiator and a heated car engine by constantly and uniformly removing excess heat into the atmosphere.
Engine cooling fan - types of device
The design of this mechanism, which is often called a radiator fan, is quite simple. It provides for one pulley on which four or more blades are placed. In relation to the plane of rotation, they are mounted at a certain angle, due to which the intensity of air injection increases (below we will tell you exactly where the fan blows).
The design also includes a drive. It can be: hydromechanical; mechanical; electric. The hydromechanical type drive is a hydraulic or special viscous coupling. The latter receives the required movement from the crankshaft. Such a coupling partially or completely blocks when the temperature of the silicone compound filling it rises.
The increase in temperature itself is caused by an increase in the load on the vehicle engine, which occurs with an increase in the number of crankshaft revolutions. The fan turns on the moment the clutch locks. But the hydraulic clutch unit turns on when the volume of oil in it changes. This is its fundamental difference from the viscous device.
By mechanical we mean a drive performed by a belt drive from. On modern cars it is practically not used, since significant power of the internal combustion engine is expended to rotate the fan (the engine gives off too much of its power). But the electric drive, on the contrary, is used very often. It consists of two main components - a control system and an electric motor for the engine cooling fan.
The control system monitors the temperature of the car's engine and ensures the functioning of the cooling mechanism. The drive electric motor is connected to the on-board computer. The control circuit of a standard electric drive consists of:
- ECU();
- a temperature sensor that monitors the temperature of the coolant;
- air flow meter;
- a relay (essentially a regulator), upon whose command the fan turns on and off;
- sensor for counting crankshaft revolutions.
The actuator in this case is the electric motor that provides the drive. The principle of operation of the announced circuit is quite simple: sensors transmit messages to the ECU; the electronic unit where the signals arrive processes them; After analyzing the messages, the ECU starts the fan regulator (relay).
Many cars of recent years of production do not have a regulator in their design, the commands of which turn the fan on and off, but a separate control unit. Its use guarantees more economical and truly efficient functioning of the entire cooling system (the unit always knows where the fan is blowing, at what angle it is located, when it is necessary to turn off the device, and so on).
Diagnosis of cooling fan faults
Neither the most innovative electric motor with high power, nor the ultra-reliable control unit or controller is able to protect the cooling system one hundred percent from breakdowns. Considering that a failed cooling fan that blows in the wrong direction or does not rotate at all can cause engine overheating, it is necessary to constantly monitor its normal functioning.
Timely repair of system components will save your car from many troubles, but it is important to correctly determine the cause of the fan failure. In other words, you first need to find a problem where, for example, the crankshaft speed controller or control unit or electric motor does not work. Any driver can diagnose fan malfunctions based on the recommendations below.
The check should begin by dismantling the connector (plug) of the temperature sensor and inspecting it. In cases where the sensor is single, you need to take a small piece of ordinary wire and close the terminals in the plug. If the fan is working properly, the control unit or relay should give a command to turn it on when closed. If the device we are interested in does not turn on during such a test, this means that it requires repair or replacement.
If there is a double temperature sensor, the testing principle changes slightly and is performed in two stages:
- The red and red-white wires are closed. In this case, the fan should rotate slowly.
- Red and black wires are connected. The rotation should now speed up significantly.
If rotation is not observed, the fan will have to be removed and a new device installed in its place. If the radiator cooling fan is constantly running (blowing without interruption), there is a possibility that the sensor for its activation has failed. It is not difficult to verify this suspicion. You must turn on the ignition and then remove the wire tip from the sensor.
If the device does not turn off after this, you can safely buy a new regulator (sensor) for turning off the device. Situations where the radiator cooling fan is constantly running are not uncommon, and now you know how to solve this problem. It also makes sense to check the fuse in cases where you doubt the functionality of the mechanism described in the article. This is done like this:
- from the positive terminal of the battery, power is supplied to the red-black or red-white wires in the fan connector;
- From the negative terminal a charge is supplied to the brown wire.
If the regulator or unit does not respond (the device does not turn on), check the temperature sensor wire (all connectors and plugs on it). The cable may need simple repairs (for example, insulating it, replacing the plug). If the problem is not in the wire, then you will have to purchase a new fan, since yours is broken.
Do-it-yourself dismantling, maintenance and repair of a cooling fan
A decent level of cooling of the radiator and engine of the machine is achieved only if the fan is periodically checked for various minor damage and contamination. It is not at all difficult to regularly perform such a check and use a brush to clean the device from dirt and dust.
The principle of dismantling the fan is simple: remove the ground wire from the battery; disconnect all wires without exception that are suitable for the node in question; Unscrew the bolts securing the device. Now you can slightly move the fan shroud and look at its condition. Such an inspection allows you to identify many breakdowns and perform:
- Stripping and replacing wires: their poor contact is often the reason for inadequate fan operation.
- Repairing brushes (or rather replacing them): this element of the system fails more often than others, since the brushes wear out very quickly, collecting all the dirt from the road.
- Elimination of short circuit or breakage of the rotor windings: sometimes they are in working condition, but do not function well due to contaminants accumulated on them. Solving this problem is not at all difficult - just soak a rag in solvents and thoroughly clean the windings (if necessary, you can also use special cleaning brushes).
Sometimes it is necessary to change the electric motor (for example, when the fan does not start when the engine is well warmed up). Unfortunately, this important part of the cooling device cannot be repaired.
Where does the cooling fan blow?
In this article we cannot ignore the question of where the mechanism that interests us blows. This is exactly what users ask experts and fellow car enthusiasts on dozens and hundreds of forums dedicated to vehicle maintenance. In fact, the answer to this is very simple.
The very purpose of the cooling device and the principle of its operation, described above, tells us that it blows exclusively on the engine, sucking in cold air through the radiator.
If in your car the air flow is directed not to the engine, but to the radiator, this only means that the fan was connected incorrectly after maintenance or repair work. Most likely, the terminals were simply mixed up. Install them correctly and never again wonder where the fan should direct the flow of cooled air.
An excellent scheme for those who want to set the engine cooling temperatures themselves. You can set the threshold for turning on the cooling fans in the range from 15 degrees to 150 degrees. What does it mean? This means that in a very hot summer, when stuck in a traffic jam, I can turn on the fan forcibly or set the temperature much lower than the one set for turning on (this way the car will not boil and overheat). Well, in very cold times I can heat it up so as not to freeze myself)
So this is not a clever circuit that was soldered together
In real life she looks like this)
It is connected to the ignition or through a fuse to the positive, but the second contact is naturally to the negative) has an LED (power-on control light), two outputs to the relay (plus and minus), and one wire is connected to the temperature sensor or ohm sensor)
Let me remind you of my problem) Due to the fact that my car now has slightly different wiring, and the brains have been changed, the cooling fan, when starting the engine, turns on at second speed and does not turn off until the car engine stops completely (((but thanks to this not clever scheme, I overcame this problem) You can say without a collective farm, but by tuning) (in my understanding, a collective farm means cutting off the wires, installing a forced-on button in the cabin. This is not correct, because when driving a car you need to enjoy the ride, and not think about when to turn it on fan so that the engine doesn't boil! Well, about tuning) With this circuit, I can adjust the temperature at which the fan turns on from 15 degrees to 150 degrees. What does this mean? This means that in a very hot summer, when stuck in a traffic jam, I can turn on the fan forcibly or set the temperature much lower than the one set for turning on (this way the car will not boil and overheat). Well, in very cold times I can warm it up so as not to freeze myself) and of course this circuit is mounted in the case and takes its place near the relay blocks in the cabin under the dashboard, or under the hood.
And this is what the body looks like and the finished version
In this scheme, the fan or cooler of the cooling system is controlled by a thermistor signal for a specified period of time. The circuit is simple, assembled with only three transistors.
This control system can be used in a variety of areas of life where cooling by means of a fan is necessary, for example, cooling a PC motherboard, in audio amplifiers, in powerful power supplies and in other devices that may overheat during operation. The system is a combination of two devices: a timer and a thermal relay.
Description of the operation of the fan control circuit
When the temperature is low, the resistance of the thermistor is high and hence the first transistor is turned off because the voltage at its base is below 0.6 volts. At this time, the 100 µF capacitor is discharged. The second PNP transistor is also off, since the voltage at the base is equal to the voltage at its emitter. And the third transistor is also locked.
As the temperature increases, the resistance of the thermistor decreases. Thus, the voltage at the base of the first transistor increases. When this voltage exceeds 0.6 V, the first transistor begins to pass current, charging the 100 uF capacitor and applies a negative potential to the base of the second transistor, which opens and turns on the third transistor, which in turn activates the relay.
After the fan turns on, the temperature decreases, but the 100uF capacitor discharges gradually, keeping the fan running for some time after the temperature returns to normal.
The trimmer resistor (shown as 10 kohm in the diagram) should have a resistance value of about 10% of the thermistor resistance at 25 degrees. Thermistor used is EPCOS NTC B57164K104J at 100 kOhm. Thus, the resistance of the substring resistor (10%) is 10 kOhm. If you cannot find this model, you can use another one. For example, when using a 470 kOhm thermistor, the trimmer resistance will be 47 kOhm.
Connection diagram for a fan powered by 12 volts.
Connection diagram for a fan powered by 220 volts
You can see two trimming resistors on the printed circuit board. The first is at 10 kOhm to adjust the fan threshold, the second at 1 mOhm allows you to adjust the operating time after the temperature has normalized. If you need a longer time interval, the 100 µF capacitor can be increased to 470 µF. The 1N4005 diode is used to protect the transistor from inductive surges in the relay.
