Soldering station schematic - Page 1
Forum section: electronics / beginners

author: mike_mike
author_rank: Super Contributor
timestamp: August 22, 2019, 08:20:26 am
content: Hello,Please have a look at the attached schematic and tell me how can I test the over temperature protection for the soldering iron ?

author: ledtester
author_rank: Super Contributor
timestamp: August 22, 2019, 08:38:00 am
content: Get a soldering iron thermometer:

author: mike_mike
author_rank: Super Contributor
timestamp: August 22, 2019, 08:40:35 am
content: I mean how can I test the overtemperature protection by only reading the temperature from thermocouple ?

author: ledtester
author_rank: Super Contributor
timestamp: August 22, 2019, 08:58:47 am
content: Is "over temperature protection" different from temperature regulation?Temperature regulation means that the control circuit will try to maintain a constant temperature at the thermocouple. Of course this means that that the heater will be turned off when the thermocouple reads a temperature greater than the temperature set by the user.By using the thermometer you can test if temperature regulation is working.

author: mike_mike
author_rank: Super Contributor
timestamp: August 22, 2019, 09:13:34 am
content: I don't know if over temperature protection is different from temperature regulation. Can you please clarify ?

author: ledtester
author_rank: Super Contributor
timestamp: August 22, 2019, 09:26:11 am
content: Temperature regulation is exactly what a soldering iron is supposed to do. It turns the heater on when the thermocouple senses a temperature lower than the desired temp and it turns the heater off when it senses a temp higher than the desired temp.I don't know what "over temperature protection" is, but it seems to be covered by temperature regulation.

author: mike_mike
author_rank: Super Contributor
timestamp: August 22, 2019, 11:07:13 am
content: Quote from: ledtester on August 22, 2019, 09:26:11 amI have understood already this type of functionality.LE: I verified the temperature regulation and it seems to work, the voltage at the thermocouple wires is constant over time. I set the minimum voltage at about 10mV, and the maximum at about 20mV.It is possible in this schematic to set the maximum temperature of the soldering iron at for example 400 C, and the temperature when the protection power off the soldering iron to a higher temperature, say 450 C ?

author: ledtester
author_rank: Super Contributor
timestamp: August 22, 2019, 03:31:02 pm
content: You can adjust the range settable by the user by adjusting R21 and R24.This is a very simple temperature controller. If the user sets the desired iron temperature to 400, the heater will turn off when the thermocouple senses any temperature > 400. There is no PID control mechanism here. In what scenario do you envision the iron reaching 450 when the user has set a temperature of 400?

author: mike_mike
author_rank: Super Contributor
timestamp: August 22, 2019, 03:47:01 pm
content: Quote from: ledtester on August 22, 2019, 03:31:02 pmI was not thinking correctly. I misunderstood some things about the functionality of the circuit.

author: mike_mike
author_rank: Super Contributor
timestamp: November 24, 2019, 09:06:33 pm
content: One more question regarding the schematic from the 1st message: how can I measure correctly the current that flows through the LED and through the optocoupler emitter led ?All I know is that the mentioned current is limited by the 50 ohm resistor. But I can't figure out the output voltage of the op amp. The op amp is supplied with 5V, but how can I figure the voltage drop between the supply voltage and the output of the op amp ?LE: I found that the output voltage of the op amp is V supply - 1.5V. Is that true if I use LM324 from any of ST, On Semi or TI ?

author: mike_mike
author_rank: Super Contributor
timestamp: March 19, 2020, 05:11:30 pm
content: Hello,I built the attached schematic, but I found that when the LED light up or down it flashes. Is that an issue of the schematic or it is normal ? If yes, what should I do to remove that blinking of the led ?I also tried the specified modifications from the image, but the soldering station does not work differently.

author: Zero999
author_rank: Super Contributor
timestamp: March 19, 2020, 06:31:48 pm
content: Quote from: ledtester on August 22, 2019, 09:26:11 amOver temperature protection is required to protect against fire in case the temperature regulation system fails. Suppose the TRIAC controlling the element fails closed circuit or the connection to the thermocouple is broken? The element will turn on continuously. If there's a risk that it could get hot enough to meltdown and catch fire if the element is powered continuously, then there needs to be something else to cut power to the element. This is done by a one shot thermal fuse inside the soldering iron's element and isn't something the temperature controller needs to deal with.