Overheating protection circuit

Thread Starter

Don_Fila

Joined Nov 26, 2021
56
I have 2200 watt heating element with thermocouple embedded inside the heating element. I used triac and other components to control the low and highness of the temperature. But my problem is how to use thermocouple to detect the temperature of the heating element and turn off automatically when it get overheated and restart when it cool down
 

Irving

Joined Jan 30, 2016
2,421
You need a thermocouple interface chip and some intelligence (virtually any small microcontroller) to control the switching of the triac.
 

Thread Starter

Don_Fila

Joined Nov 26, 2021
56
Last edited by a moderator:

Irving

Joined Jan 30, 2016
2,421
Can you please help me with any diagram?
Shortly, it's essentially the innards of the device @Danko suggested. But let's be clear about your expectations; are you looking for accurate temperature control or just overheat protection? The latter is simpler. What is the purpose of the hot air (gun?) and where did it originate from?
 

Thread Starter

Don_Fila

Joined Nov 26, 2021
56
You did not mention learning as a requirement. Try to not blame others for your frustration.

You could certainly learn something by reading the instructions and observing the operation.
It has been observed
Shortly, it's essentially the innards of the device @Danko suggested. But let's be clear about your expectations; are you looking for accurate temperature control or just overheat protection? The latter is simpler. What is the purpose of the hot air (gun?) and where did it originate from?
Wow I really love this question!!! and the answer is OVERHEAT PROTECTION.
 

Thread Starter

Don_Fila

Joined Nov 26, 2021
56
It has been observed

Wow I really love this question!!! and the answer is OVERHEAT PROTECTION.
Shortly, it's essentially the innards of the device @Danko suggested. But let's be clear about your expectations; are you looking for accurate temperature control or just overheat protection? The latter is simpler. What is the purpose of the hot air (gun?) and where did it originate from?
I have to answer your questions in a listing form:
1. Overheat protection
2.The purpose of the hot air gun : it's an smd tool that is used to solder or desolder an electronic components on a pcb. It contains heating element(2200 watt),fun(24v dc),reed switch and thermocouple
3.where did it originate from : China
 

Irving

Joined Jan 30, 2016
2,421
I have to answer your questions in a listing form:
1. Overheat protection
2.The purpose of the hot air gun : it's an smd tool that is used to solder or desolder an electronic components on a pcb. It contains heating element(2200 watt),fun(24v dc),reed switch and thermocouple
3.where did it originate from : China
Hmmm, OK.

My hot air gun is fully temperature controlled which is essential for SMD work. Yours has no temperature control? The thermocouple wasn't used? Weird...

Anyway, here is an example circuit that will do simple analog overheat control. Because of the small voltages from a thermocouple the front end amplifier AD8495 is very sensitive and needs to be built on a properly laid out PCB. The trimmer pot RV1 sets the temperature between approx 88 and 425°C. The relay is ON when the temperature is below the set point, it goes OFF when the temperature goes above the set point and stays off until the temperature has dropped by approx 10°C at 100°C and 70°C at 400°C (set by R7). I've assumed the thermocouple is a 'K' type because that is the most common.

1638807776298.png
 

Thread Starter

Don_Fila

Joined Nov 26, 2021
56
Hmmm, OK.

My hot air gun is fully temperature controlled which is essential for SMD work. Yours has no temperature control? The thermocouple wasn't used? Weird...

Anyway, here is an example circuit that will do simple analog overheat control. Because of the small voltages from a thermocouple the front end amplifier AD8495 is very sensitive and needs to be built on a properly laid out PCB. The trimmer pot RV1 sets the temperature between approx 88 and 425°C. The relay is ON when the temperature is below the set point, it goes OFF when the temperature goes above the set point and stays off until the temperature has dropped by approx 10°C at 100°C and 70°C at 400°C (set by R7). I've assumed the thermocouple is a 'K' type because that is the most common.

View attachment 254346
It's really informative .
 

Irving

Joined Jan 30, 2016
2,421
This is what I was looking and expecting other members to tell me.
To be fair to other members, not everyone has the time to pull something together like this from scratch. This is based on something I did a while back for a completely different purpose and I've just added a simple comparator on the end. It should work, but I wouldn't bother trying if you don't have the ability to lay out a proper PCB as you'll just be chasing random problems. I've not looked to see if you can by a thermocouple amp off-the-shelf and just add the back-end.

The other approach is a digital thermocouple interface eg this Adafruit board but you then need a microcontroller to interface it to, and software to configure and operate with it. Which is arguably easier if you have the knowledge to do so, but not everyone is a software engineer. That would be my preferred route as then you can add bells n whistles like a temperature display or completely close the loop and provide digital temperature stabilisation, not just overheat control. All of which adds complexity.
 

Thread Starter

Don_Fila

Joined Nov 26, 2021
56
To be fair to other members, not everyone has the time to pull something together like this from scratch. This is based on something I did a while back for a completely different purpose and I've just added a simple comparator on the end. It should work, but I wouldn't bother trying if you don't have the ability to lay out a proper PCB as you'll just be chasing random problems. I've not looked to see if you can by a thermocouple amp off-the-shelf and just add the back-end.

The other approach is a digital thermocouple interface eg this Adafruit board but you then need a microcontroller to interface it to, and software to configure and operate with it. Which is arguably easier if you have the knowledge to do so, but not everyone is a software engineer. That would be my preferred route as then you can add bells n whistles like a temperature display or completely close the loop and provide digital temperature stabilisation, not just overheat control. All of which adds complexity.
Hmmm ok
 

Irving

Joined Jan 30, 2016
2,421
OK then. Here's the "Arduino" version. I've used a Nano 3 but any decent microcontroller will do.

1638828461411.png

Some simple code (not tested).. Doesn't use /DRDY interrupt but polls for conversion complete

Thermocouple.ino:
#include <Adafruit_MAX31856.h>

#define HIGHPOINT 400
#define LOWPOINT 350
#define RELAY 4

Adafruit_MAX31856 myThermocouple = Adafruit_MAX31856(10, 11, 12, 13);

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(RELAY, OUTPUT); // relay control pin
  myThermocouple.begin();
  myThermocouple.setThermocoupleType(MAX31856_TCTYPE_K);
  myThermocouple.setConversionMode(MAX31856_ONESHOT);
}

void loop() {
  // put your main code here, to run repeatedly:
  myThermocouple.triggerOneShot();//start conversion
  while(!myThermocouple.conversionComplete()){ delay(25); } //wait till done...
  float temperature = myThermocouple.readThermocoupleTemperature();
  Serial.println(temperature);
  if(temperature>=HIGHPOINT)
    digitalWrite(RELAY,LOW); //turn off
  else
    if(temperature<=LOWPOINT)
      digitalWrite(RELAY, HIGH); // turn on
}
 

Thread Starter

Don_Fila

Joined Nov 26, 2021
56
OK then. Here's the "Arduino" version. I've used a Nano 3 but any decent microcontroller will do.

View attachment 254372

Some simple code (not tested).. Doesn't use /DRDY interrupt but polls for conversion complete

Thermocouple.ino:
#include <Adafruit_MAX31856.h>

#define HIGHPOINT 400
#define LOWPOINT 350
#define RELAY 4

Adafruit_MAX31856 myThermocouple = Adafruit_MAX31856(10, 11, 12, 13);

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(RELAY, OUTPUT); // relay control pin
  myThermocouple.begin();
  myThermocouple.setThermocoupleType(MAX31856_TCTYPE_K);
  myThermocouple.setConversionMode(MAX31856_ONESHOT);
}

void loop() {
  // put your main code here, to run repeatedly:
  myThermocouple.triggerOneShot();//start conversion
  while(!myThermocouple.conversionComplete()){ delay(25); } //wait till done...
  float temperature = myThermocouple.readThermocoupleTemperature();
  Serial.println(temperature);
  if(temperature>=HIGHPOINT)
    digitalWrite(RELAY,LOW); //turn off
  else
    if(temperature<=LOWPOINT)
      digitalWrite(RELAY, HIGH); // turn on
}
Thank you very much your help.
 
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