Solving Relay Problem in Thermistor Controlled Comparator Circuit

  • Thread starter Ali Inam
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In summary, the speaker has created a circuit using a thermistor and a relay to control a fan based on temperature. However, they are experiencing a problem with the relay switching rapidly in normal conditions. To solve this, they suggest introducing hysteresis by providing feedback from the output voltage to the opamp.
  • #1
Ali Inam
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Hello everyone, I've made a thermistor controlled comparator circuit which has got a relay connected to its output, when the temperature of the thermistor rises, the relay switches and the fan on its output is turned on the coll the thermistor down.

Now, my circuit is working perfectly, but I'm getting a problem with my relay, which is that in normal condition when the coil of the relay is not being charged from the thermistor output, my relay is switching extremely fast and again and again, it switches from NC to NO then again from NO to NC at about twice or thrice per second. But when the coil is charged, it then switches permanently to start the fan connected to it.

I don't know what I must do about the problem I'm facing in the normal condition.

Thanks...!
 
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  • #2
First, unless the current through the thermistor is what is heating the thermistor, a fan will not cool it. In fact due to the power dissipated by the fan, it will heat the air slightly. The reason blowing air over skin feels cool is that it aids evaporation of perspiration which does cool the skin.

To avoid the condition you describe in which the relay is switching rapidly from one state to the other, hysteresis is introduced by feeding back a small amount of the output voltage to the the non-inverting (+) input of the opamp. I would start with about 1% and adjust it up or down from there.
 
  • #3
Ali Inam said:
Hello everyone, I've made a thermistor controlled comparator circuit which has got a relay connected to its output, when the temperature of the thermistor rises, the relay switches and the fan on its output is turned on the coll the thermistor down.
Can you show the circuit here?
 

Related to Solving Relay Problem in Thermistor Controlled Comparator Circuit

1. What is a thermistor controlled comparator circuit?

A thermistor controlled comparator circuit is a type of electronic circuit that uses a thermistor, a temperature-sensitive resistor, to control the switching of a comparator. The comparator compares the voltage from the thermistor with a reference voltage and outputs a digital signal based on the comparison.

2. How does a thermistor controlled comparator circuit work?

In a thermistor controlled comparator circuit, the thermistor is connected in series with a resistor to form a voltage divider. As the temperature changes, the resistance of the thermistor changes, which affects the voltage at the junction of the two resistors. This voltage is compared to a reference voltage by the comparator, and the output changes from high to low or vice versa depending on the comparison result.

3. What is the purpose of using a thermistor in a comparator circuit?

The thermistor serves as a sensor in the comparator circuit, providing a variable input based on temperature. This allows the circuit to be used for applications such as temperature sensing, temperature control, and temperature compensation.

4. What are some common problems encountered when solving relay problem in thermistor controlled comparator circuit?

Some common problems that may be encountered when solving relay problem in thermistor controlled comparator circuit include incorrect wiring, incorrect reference voltage, and component failure. It is important to carefully check all connections and components and troubleshoot any issues that may arise.

5. How can I troubleshoot and solve relay problems in a thermistor controlled comparator circuit?

To troubleshoot and solve relay problems in a thermistor controlled comparator circuit, you can follow these steps:

  • Check all wiring and connections to ensure they are correct and secure.
  • Verify that the reference voltage is set correctly.
  • Use a multimeter to check the resistance of the thermistor at different temperatures to ensure it is functioning properly.
  • Check the datasheet of the comparator and other components to ensure they are being used correctly.
  • If all else fails, try replacing the thermistor or other components to see if that solves the problem.

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