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Soldering iron question

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2010 - » Archive through 13 January, 2012 » Soldering iron question « Previous Next »

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bruce
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Username: bruce

Post Number: 727
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Posted on Saturday, 31 December, 2011 - 10:36 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hello guys,
I have just started a new thread, with the above title, but regrettably, I have posted it as an attachment to Terry's 'LED Ammeter' thread by mistake.
Apologies for the c**k-up. Perhaps, if you have an answer to the original question, you could post it in this thread. Thanks

bruce
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gordon
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Posted on Saturday, 31 December, 2011 - 10:47 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Rapid have a range of thermistors suitable for 300C. I think a temperature controlled soldering iron has some sort of thermocouple near the heating element for temperature control.

http://www.rapidonline.com/Electronic-Components/Glass-encapsulated-miniature-thermistors-61187
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ant
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Posted on Saturday, 31 December, 2011 - 01:42 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

We've (nearly) all done it, Bruce! To save fiddling about, here's the post. I believe that Weller, at least, has a magnet in the bit which has a well-defined Curie temperature which operates a reed switch in the element - regards Ant



Hello guys, and HNY,
The title of this thread is a bit vague, I realise, but read on, McDuff...

I have in mind a project in which a small slug of brass is to be heated to around 200 deg C. Incidentally, solder melts at all sorts of different temperatures, all in the region of 200 deg, IIRC, but isnt the temperature of the iron around 400 deg?
To control the temperature of this brass 'slug' you need some kind of feedback. I dont think a thermistor would survive, would it? I guess you'd need a thermocouple ( BTW, how do you affix a thermocouple bead to a brass rod in a way which will survive that kind of temperature? )

How do temperature-controlled soldering irons actually control their temperature?

bruce
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dselec
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Posted on Saturday, 31 December, 2011 - 04:42 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Platinum resistance thermometers (PRTs) offer excellent accuracy over a wide temperature range (from -200 to +850 °C)
http://www.picotech.com/applications/pt100.html
You can use pt 100 if money is not a problem.
option 2 add a simple triac contrl. with pot. and mark out diff. settings for diff. resistance .

p.s. i think u have same post in the ammeter...
u can ask support to remove that.

(Message edited by dselec on 31 December, 2011)
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alec_t
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Posted on Saturday, 31 December, 2011 - 06:52 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

AFAIK commercial temp-controlled irons use the Curie-point method that Ant mentioned. But surely it should be possible to use the (albeit small) change in resistance of the heating element in an ordinary iron to sense temperature? I envisage a circuit which briefly in each cycle (or even every few seconds) disconnects the power from the element and instead connects the element in a resistor bridge circuit. The bridge output would be amplified, rectified if necessary, and fed to a comparator controlling the iron power supply.
Come on, guys; get your thinking caps on! A 2012 project.

And, HAPPY NEW YEAR!
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ant
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Posted on Saturday, 31 December, 2011 - 07:08 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hello Alec,

Presumably my British-made Antex irons aren't Curie-operated as they're adjustable?

Regards Ant
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bruce
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Posted on Saturday, 31 December, 2011 - 07:28 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hello,
I think I've lied to you: I thought I would need a temperature of 200 plus deg, but that might not be true.
The first thing I have to do is to see at what temperature my 'weld' works. I wont bore you with the details, just watch this space...

bruce

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