Ask the master to help analyze the temperature fan control circuit urgent !

1. How does the thermistor value reach the standard resistance?

Answer: Thermistors are based on the ambient temperature of 25 degrees Celsius.

2. What is the role of R4?

Answer: R4 is an adjustable resistor, here it is to adjust the DC potential of the base of the transistor, and functionally this resistor is to adjust the starting voltage point of the fan.

3. What are the functions of C, C1, C2, etc.?

Answer: They are all filter capacitors, but the frequency points of each capacitor are different, C 220UF, 50Hz pulsating DC after filtering rectification, C1, generally we use this capacity of porcelain or polyester to filter out 500kHz AC ripple, C2, filter out 1MHz AC ripple.

4. What are the normal working conditions of the transistor?

Answer: The triode VT1 and VT2 form a composite tube, and its working condition is that the base voltage of VT1 is calculated at an ambient temperature of 25 degrees Celsius, that is, R4 is adjusted to , and the relay is engaged.

Let the resistance of R4 be X

12v/(10k+x+8k))*x+8k)=5v+x＝

5. In fact, if this circuit is changed like this, it will be safer and more stable.

C C1 Filter Capacitor Filter AC Voltage C2 is 7802 Regulator 12 Output Filter Capacitor R4VT1 Offset Resistance Control VT1 Base Current.

c mainly plays an important role in energy storage filtering, and C1 and C2 are filters. When the value of R4 increases or the resistance value of R3 decreases to a certain value, so that the negative value of D1 is greater than 5V, D1 is broken down, the triode VT1 is turned on, and then VT2 is also turned on, and the relay is engaged.

A temperature switch can be connected in series, and the degree can be selected.

Pre-embedded thermocouple or thermal resistance Thermostat Installed Output point connected to fan control loop You can also add overtemperature indicator light and audible and visual alarm.

This fan is just an actuator.

It is controlled by thermistors or temperature relays or other components.

When the temperature reaches 80 degrees, the thermistor action fan starts to dissipate heat, and the temperature is also heated below a certain temperature.

Note: A thermistor can only detect one temperature, that is, it is not adjustable, while a relay is adjustable.

How the fan controls the temperature can only control the amount of wind.

Used in series, normally open, normally closed. The temperature can be selected.

It's very simple, you just use a rotten induction cooker to change it. It's up to you as many times as you want.

What fan? If it's an electric fan at home, it's useless, it's just to speed up air circulation.

As for the fan in the computer, many big brands of motherboards have similar software, but if you want to do it yourself, use a thermistor and a transistor to control the fan current, so as to control the speed, and make a simple temperature control fan. If it's more complicated only through probes and software ... Seek the best together**!

Your control fan system must have a temperature sensor to detect temperature B, and the data measured by temperature B must be identified by a single-chip microcomputer; At the beginning, the temperature A is written in the microcontroller, so that our microcontroller has two temperatures, A and B; Next, you need to add two stages of programs to the single-chip microcomputer, first, the fan start and stop program (if BA, then the fan (motor start)), second, the fan speed program, it is recommended to give a few temperatures in segments, and then correspond to several corresponding speeds (in fact, it is the PWM output of several specific cycles), and finally, find the corresponding PWM output according to the measured temperature;

You need to learn at least the use of the universal IO port of the 51 single-chip microcomputer, the simple C language, the driving mode of the PWM to the stepper motor, and the collection of the temperature signal of the single-chip microcomputer (some sensors directly output digital signals, compared with the analog temperature sensor, there is less AD conversion part, and the software and hardware design can simplify a part).

First of all. The scheme of using temperature to control the electric fan is unrealistic, because it is basically uncontrollable, because the function of the electric fan is only to speed up the air flow, and it does not change the temperature of the air, so it is impossible to talk about using temperature to control the electric fan.

To learn this, there are so many gadgets that you can do with your hands. As zhougan8 said: first go to learn single-chip microcomputer, 51 or pic.

Let's go learn the MCU first, 51 or pic. With a temperature sensor. Just add a thyristor.

RTD + thermostat + power regulator + fan.

To put it bluntly, let the fan work when it's hot, and stop when it's cold. **There is a finished thermostat on it. What kind of software to write, just buy one and it's OK. It's all invented.

It may be caused by the oxidation of the contacts in the relay and the low voltage in the rear section!

Two suggestions; Split the year 1, and paste some silicone to the CPU so that the heat dissipation is good, and the fan will turn slightly slower.

2. The brigade dismantles the fan to drop some lubricating oil Do not use cooking oil It is best to use mechanical oil. See the effect absolutely no problem. Hehe.

3.This temperature and speed is normal.

There is no problem at all, 3 and 4 are used the same. The temperature is also normal. But the fan is a little noisy, so I don't know what to do.

If the speed is high, the temperature will be low, so the noise will be loud!

My 5000+ transfer number is about the same as yours, but the temperature is at 40, and the consequences of the CPU exceeding are clear!