Variable soldering iron heater construction and operation questions

[caphair]

I have a variable soldering iron that uses 24v 50w heating elements.

I'm wondering how the temperature is controlled, is the 24vac constant and pulsed per setting or is it like a light dimmer where it operates in any range up to 24vac?

Also the heating element itself, I noticed one end has another wire twisted to it which is then spot welded to the wire that is soldered on the PCB of the iron. Curious why only one end is twisted with another wire and not both sides?

[capwizard]

Re: Variable soldering iron heater construction and operation questions

A good solder station's temperature is control by PID (proportional–integral–derivative) controller.

Cheap one uses light dimming circuit that has no feedback so the temperature of the soldering iron tip is not precision.

That wires are thermocouple which is two different kind of metal wires welded together.

[caphair]

Re: Variable soldering iron heater construction and operation questions

The wires are coming from the heater element not the thermocouple. The thermocouple wires are the red and blue

[capwizard]

Re: Variable soldering iron heater construction and operation questions

I bet you the red and blue wires are heating element. you can distinguish both by using meter test those resistances.

Thermal copper is almost like a short under one ohm and heating element will be around 6 or 20 ohm.

[eccerr0r]

Re: Variable soldering iron heater construction and operation questions

Usually thermocouples aren't wound in a tight spiral like heater elements, but don't know, that solder iron heater looks weird.

[stj]

Re: Variable soldering iron heater construction and operation questions

interesting picture.

[capwizard]

Re: Variable soldering iron heater construction and operation questions

It's not fair, I didn't see it clearly. Because I used my mobile phone at work, I went home and saw it with pc, I found out the heating coil was out side the ceramic tube. WOW....I lost my bet.

[redwire]

Re: Variable soldering iron heater construction and operation questions

24VAC soldering station controllers use "bang bang" control.

PID control is not useful because there is a huge delay caused by the thermal resistance from the heating coil to the tip, and the tip has large thermal mass. So the heat transfer is poor (ceramic) and a tip takes a while to heat up.
There is also error because the thermocouple sort of is in the middle, between heater and tip. None of this is ideal which is why Hakko integrated everything into one cartridge.

Say, for 50% output or 1/2 heat you pulse the heater on and off every second, compared to using phase-control delaying the TRIAC firing 90°. The time constant for a soldering iron heater+tip is long and it just averages out the same.

Bang-bang (on/off) control is preferred because the thermocouple signal gets alot of AC hum when the heater is on. It would be worse with phase-control, the noise from the heater pulse can swamp the thermocouple signal. Again, new Hakko stations shut off the heater, sample temperature, and then turn heat back on, to get around this problem.

This also may be why you see a lop-sided heating coil. The ground side of the heating element can affect noise (hum) the thermocouple picks up, it needs to be closest.

I see a two-wire tunnel for the thermocouple wires. You can prove it's a thermocouple because (+) lead is magnetic and (-) is not, and pretty much a short circuit. Type J output is only 1.28mV at room temp and 27.4mV at 500°C/932°F.
Nichrome wire does not solder, so that could explain the spot-welded splices.

https://cdn.badcaps-static.com/pdfs/...bff0741553.pdf

[caphair]

Re: Variable soldering iron heater construction and operation questions

Yes the outside ceramic tube is removed. And if you notice one end of the heating coil I had another wire twisted around it but the other end doesn’t. That’s what I’m curious about, is there a reason for that?

[redwire]

Re: Variable soldering iron heater construction and operation questions

I can't see the other end, but I think the heater wire is doubled-up for the center run, so it doesn't heat up. You want the outside coil as the heater, not the center run glowing orange hot.
It's still odd because there are three wire ends, where is the fourth

[capwizard]

Re: Variable soldering iron heater construction and operation questions

24VAC soldering station controllers use "bang bang" control.

Thank you for your exquisite explanation.

Soldering station controllers, there are two more other methods besides you mentioned, one is OK International SmartHeat soldering irons, another one is brain controled poor-man's soldering iron by me.

One day, my friend brought a big black box with a tiny soldering iron. Told me, he paid $1200, that was the SmartHeat soldering iron not even has a temperature display just like my poor-man's soldering iron. Both are simple and powerful.

Poorman's soldering iron is the only one in the world could use both AC and DC 24 volt and does bronze brazing job and has self-destructing features if you press more than 20 minutes.


Metcal, the original SmartHeat Soldering inventor
https://www.youtube.com/watch?time_c...&v=S9Wmqc9O24w

Metcal SmartHeat Powered MFR-1110 Soldering and Rework
https://www.youtube.com/watch?v=RWU6yT9pb2M

---------------------------------------------------------------
OK International Metcal

Metcal Smart Heat Provides power on demand in response to the thermal load.

SmartHeat soldering irons approach manual soldering in a totally different way: it is the tip temperature that is kept constant and not the power supplied to it, and the power varies automatically. SmartHeat detects the increase in thermal load demanded by the larger heat capacity of a bigger joint and compensates by increasing the power.


how SmartHeat really works?
http://blog.okinternational.com/metc...rks-a-tutorial

[Curious.George]

Re: Variable soldering iron heater construction and operation questions

PID control is not useful because there is a huge delay caused by the thermal resistance from the heating coil to the tip, and the tip has large thermal mass. So the heat transfer is poor (ceramic) and a tip takes a while to heat up.

That's what the D term is for -- "anticipation".

[capwizard]

Re: Variable soldering iron heater construction and operation questions

Soldering Iron PID Temperature Controller
https://www.google.com/url?sa=t&sour...rzc-m-tn93ZdxS

PID temperature controller DIY ArduinoYouTube app
https://youtu.be/LXhTFBGgskI