The ground of the soldering station, which is connected at the rectifier ground (rectifier minus) is not connected to the mains (power) ground.

So what do you think might happen?

 

I think that a potential difference will appear between the station ground and the power ground, because the grounds are not connected together.

 

I think that a potential difference will appear between the station ground and the power ground, because the grounds are not connected together.

Yes, it will. It will not be dangerous to the operator but if the circuit ground is connected to any metal parts of the station, e.g. the case, the circuit will be damaged if the soldering iron tip comes in contact with them.

 

Hello,

I am using the soldering station from this topic with good results, but I am wondering if there exists a better schematic, which has protection for the soldering iron.
Can someone please show me a schematic which has protection for soldering iron ?

Thank you in advance.

 

Hello,

I am using the soldering station from this topic with good results, but I am wondering if there exists a better schematic, which has protection for the soldering iron.
Can someone please show me a schematic which has protection for soldering iron ?

Thank you in advance.

What do you want to protect from what?

 

I was thinking about protecting the soldering iron from overheat, if the circuit of the soldering station is damaged. But I will leave this and I will guide my attention to the schematic from this site: http://electronics.vlzqz.com/analog-pid-soldering-station.html
I built today the schematic, and I do not know how to make it work correctly. The problem is that momentary I do not have the oscilloscope in my workshop, probably it will take a few months until I will get it back.
The problem is that I got maximum 14.4mV on the thermocouple, but I need 20mV in order to have a good adjustment range. I tried to turn the 2 trimmers in both directions, but I am getting maximum 14.4mV on the thermocouple. What I am missing or what should I do to make it work correctly ?

LE: I am using the same soldering iron as it is on that webpage (Gordak, with K type thermocouple).

 

I was thinking about protecting the soldering iron from overheat, if the circuit of the soldering station is damaged. But I will leave this and I will guide my attention to the schematic from this site: http://electronics.vlzqz.com/analog-pid-soldering-station.html
I built today the schematic, and I do not know how to make it work correctly. The problem is that momentary I do not have the oscilloscope in my workshop, probably it will take a few months until I will get it back.
The problem is that I got maximum 14.4mV on the thermocouple, but I need 20mV in order to have a good adjustment range. I tried to turn the 2 trimmers in both directions, but I am getting maximum 14.4mV on the thermocouple. What I am missing or what should I do to make it work correctly ?

LE: I am using the same soldering iron as it is on that webpage (Gordak, with K type thermocouple).

Try reducing the value of R1. Start with 2.2Kohms. That should let you adjust the range.

 

I made the following modifications:
1. Replaced R1 by 2k2
2. Replaced R6 by 33k
3. RV1 rotated at about half of the course
4. RV2 rotated at about 11.2k between the GND and wiper.

I am getting now about 20.2mV maximum.

Are the modifications correct ?

LE: Initially it was working fine, now the voltage from the thermocouple is varying between 11 and 13mV (with the 5k pot at about half), initially it was varying between 13.3 and 13.5mV.

 

I made the following modifications:
1. Replaced R1 by 2k2
2. Replaced R6 by 33k
3. RV1 rotated at about half of the course
4. RV2 rotated at about 11.2k between the GND and wiper.

I am getting now about 20.2mV maximum.

Are the modifications correct ?

LE: Initially it was working fine, now the voltage from the thermocouple is varying between 11 and 13mV (with the 5k pot at about half), initially it was varying between 13.3 and 13.5mV.

Where exactly are you measuring?

 

I am measuring on the place were the wires from the soldering iron enters into the PCB.

 

I made the following modifications:
1. Replaced R1 by 2k2
2. Replaced R6 by 33k
3. RV1 rotated at about half of the course
4. RV2 rotated at about 11.2k between the GND and wiper.

I am getting now about 20.2mV maximum.

Are the modifications correct ?

LE: Initially it was working fine, now the voltage from the thermocouple is varying between 11 and 13mV (with the 5k pot at about half), initially it was varying between 13.3 and 13.5mV.

The construction article stated: "Since the soldering iron handle thermocouple is a type K (I think) it produces voltages between 0mV and 19mV in the range of 0 to 450 (which was the range that was useful for this project)."
so it appears to be working. You may have to play with the values a little more to get the range you want.

 

I wanted to try another soldering station schematic, but I found that there is a mismatch between the image of the PCB and the schematic. That mismatch is located near R14. On the pcb R14 is connected to pin 5, but in the schematic is not connected to pin 5.
What should I do ?
Please have a look at the attached document ...

 

I also managed to make work the schematic with PWM, but the thermocouple voltage measured on the PCB is varying between 18 and 20mV. Sometimes it is stable at about 20mV, and sometimes it is going under 20 mV for a short period of time. I don't know if this is normal...

 

I wanted to try another soldering station schematic, but I found that there is a mismatch between the image of the PCB and the schematic. That mismatch is located near R14. On the pcb R14 is connected to pin 5, but in the schematic is not connected to pin 5.
What should I do ?
Please have a look at the attached document ...

There are a number of inconsistancies between the component designators on the schematic and the pcb. You have two chopices:
You can spend a lot of time correcting the errors or you can find another controller.
You could build the one I made. It works very well. I designed a pcb for it but I made mine on prototypr circuit board using the pcb layout as a guide.

 

There are a number of inconsistancies between the component designators on the schematic and the pcb. You have two chopices:
You can spend a lot of time correcting the errors or you can find another controller.
You could build the one I made. It works very well. I designed a pcb for it but I made mine on prototypr circuit board using the pcb layout as a guide.

Which one is correct between the schematic and the pcb ?

 

Which one is correct between the schematic and the pcb ?

I would assume that the schematic is correct.

 

I was thinking about protecting the soldering iron from overheat, if the circuit of the soldering station is damaged. But I will leave this and I will guide my attention to the schematic from this site: http://electronics.vlzqz.com/analog-pid-soldering-station.html
I built today the schematic, and I do not know how to make it work correctly. The problem is that momentary I do not have the oscilloscope in my workshop, probably it will take a few months until I will get it back.
The problem is that I got maximum 14.4mV on the thermocouple, but I need 20mV in order to have a good adjustment range. I tried to turn the 2 trimmers in both directions, but I am getting maximum 14.4mV on the thermocouple. What I am missing or what should I do to make it work correctly ?

LE: I am using the same soldering iron as it is on that webpage (Gordak, with K type thermocouple).

That looks like an interesting, and perfectly viable circuit, but there are a few things I think are potentially misleading there:

1) Unless I'm dramatically misunderstanding that circuit, it is not providing PID control all at all. It is only providing "P" (proportional) control. The heater output is proportional to the magnitude of difference between set point and measured value. The actual value will stabilize below the set point, and it will be prone to overshoot and oscillation, when compared to a properly tuned PID circuit. In this application, those differences may be harmless, so I'm not advising against using the circuit, but I do think it's misleading to call it PID.

2) Thermocouples don't provide a signal indicating a specific temperature, but rather a temperature difference. They indicate the difference in temperature between the two ends of the thermocouple wire, in this case the difference between the soldering iron and the control box. So, for example if the thermocouple voltage is 18mV, that corresponds to about 438 deg C... but that doesn't mean your soldering iron is at 438C; it means the soldering iron is at that temperature above whatever the temperature in the control box is. If that's near room temperature, the iron might be more like 460C.

As long as you're using this setup in a climate controlled room, and assuming the box doesn't heat up too, too much during use, these differences probably won't matter to you. However, if you ever want to do temperature measurements with a thermocouple, you'll need to understand this distinction.

 

I wanted to try another soldering station schematic, but I found that there is a mismatch between the image of the PCB and the schematic. That mismatch is located near R14. On the pcb R14 is connected to pin 5, but in the schematic is not connected to pin 5.
What should I do ?
Please have a look at the attached document ...

If you enjoy a challenge, reverse engineer their pcb layout into a second schematic, then compare the two schematics to see which one makes more sense and build yours accordingly.

If you just want something to work, I'd move on to something else. I've seen countless project suggestions online that are just plain wrong - proposed circuits that have obviously never been built and tested, because they can't possibly work as drawn. If the schematic and pcb layout don't match, to me that's a red flag warning that this circuit hasn't been proven. It's also possible they built something that works, perhaps without even understanding why, and just documented it poorly. In either case, they're not a reliable source of trustworthy information.

So, you can choose to take the challenge of searching for the hidden truth (if any) within their errors, or you can move on to a more reliable source if you want something with a higher chance of success.

 

Does the attached schematic has a power off mode for the soldering iron if the thermocouple voltage rise above a set value, for example above 20mV ?

 

Does the attached schematic has a power off mode for the soldering iron if the thermocouple voltage rise above a set value, for example above 20mV ?

I don't know. What does IC1B do? Where did you get the schematic from? Was there no description of it's function?