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Soldering Iron Controller Project

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MrAl

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Hi,

I see quite a few soldering irons for sale for maybe 25 dollars USD and they have three to four wires. I am guessing that the three wire ones are two for resistive element and one for temperature probe, and not sure what the four wire ones have but im sure it's not too difficult.

Question is, how hard can it be to make a controller for these things? I would think simple, with a controllable 24vdc supply for example. They are about 60 watts so figure about 3 amps.
Seems a simple controller with pass transistor, op amp, amplifier to amplify the probe signal.
No need for an LED display for the temperature.

Has anyone tried this yet?
 

dr pepper

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There have been a few projects for this, trouble is really cheap ones make it impractical.
You can make a simple on/off control with something like a lm324 quad op amp, however a full blown pid controller takes a fair bit of development.
 

MrAl

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Hi,

Actually i have no problem building a controller, the part that controls the voltage that gets to the element, as i had a learned a lot of control theory in the past. So the controller itself is no problem.
What i am not sure of is what kind of temperature sensor they use in the elements, how it is connected, stuff like that.
But really hoped someone else here had tried it already. I can guess but if someone did it already that would be faster.
 

dr pepper

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PT100's seem popular these days.
 

throbscottle

Well-Known Member
I found this to be a very useful thread when I built my 936 almost-clone: http://www.eevblog.com/forum/reviews/genuine-vs-fake-hakko-936-ceramic-heater-a1321/. A lot of effort in that thread!

Anyway, it seems the connection for Hakko and most clones is the heater and a PTC, though some clones were found to have a thermocouple.

So what I got from it was a couple of versions of 936 schematics, one (the jpg) is taken I think from a real Hakko service guide, the other is one someone has reverse engineered from an actual unit. Here's the modified version I did from them. I used LM358's because that's what I had. The original has a μPC1701C to drive the triac, which is obsolete - a comparator + zero-crossing opto-triac does the same job. I had to swap that bit around a bit when I built it because I'd got the switching sense the wrong way round - I think I changed the schematic to match but I'm not completely certain.
 

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