# Creating a low (90-250F) temperature-controlled soldering iron (or modifying a higher temp one to get lower temps)

I'm a wax sculptor and am interested in getting a temperature controlled soldering iron but I need a very low temperature range (like 100-250F). Most units come with a bottom end of 350F+. Is there a way to open up and modify one of these units easily or is it all pre-programmed in? I don't need the digital readout to report the correct temperature after any modifications but I do need the temperature control to be in-tact and working.

If it's not practical is there any way to modify a non-temperature controlled to be able to get such a range without resorting to programming some chip. I know I'd have to add in a thermocouple in or on the outside of the shaft but I wasn't sure if there are ready-to-go circuits or devices that will switch on/off the device to maintain a temperature based on a thermocouple unit.

(Actually, I have one of these right now but it's in the wrong temperature range and would be way too clunky as it's an external thermostat that does up to 108F for heating pads for plants, and I could i suppose weld the the probe of it onto the shaft of my soldering iron, if it did the right temperature range, but that'd be pretty inelegant).

Thanks!

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The answer is going to be specific to the soldering-iron in question, and not really generalizable. –  Connor Wolf Nov 1 '12 at 2:32
For what it's worth, I've run a plain-old radioshack firestarter soldering iron off a variac, for the purpose of shaping and joining wax (I took a class in bronze sculpting in college). However, a variac is expensive and you still don't get closed-loop temperature-control. –  Connor Wolf Nov 1 '12 at 2:33
Is the specific temperature setting a requirement, or would a wax pen such as the Pepe Touchamatic Digital Wax Pen (gesswein.com/p-7659-pepe-touchamatic-digital-wax-pen.aspx) work for you? –  Anindo Ghosh Nov 1 '12 at 5:36
The best I can figure at this point is to buy an existing soldering iron that goes with a true temperature controlled station. they have five inputs on the handle (the hakkos do at least), two of which I assume are the thermocouple, two are the power and one is the ground. I could then hook it up to a temperature controller which is available on ebay and works with a variety of thermocouples. I then get he advantage of a streamlined handle and replaceable heater element which has a thermocouple already embedded, but can choose a broader range of temperature than the provided base-station. –  birchbark Nov 1 '12 at 14:05
How is this a duplicate? The "duplicate" question wants to add temperature sensing to a non-temperature-controlled soldering iron. This question wants to modify a soldering iron with an existing sensor. The tasks involved with each are very different. –  Connor Wolf Nov 2 '12 at 22:21
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You can get a (TRIAC) light dimmer and wire it in a box outlet. Use a <25W small light in parallel to monitor the power input in case of inadequate load, and hysteresis effects.

You can calibrate it with power input and temperature output or set by trial and effect.

Although this is not regulated the temerpature could be proportional to % power input. (except for hysteresis)

If cooled rapidly it will return to normal temperature in a minute or so.

You may want the chisel edge or round 1/16" screw on tip with a 15W or 25W heater.

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I'm aware of the dimmer option but unfortunately it's not regulated enough for my purposes. Wax conducts heat very well so as soon as the tip comes in contact with wax the temperature drops rapidly and I can't be fiddling with it to turn it up and down. If I turn it high enough that it works well when in use then when it is not in use it will heat the wax remaining on its surface to smoke point and create fumes. Definitely need accurate temperature control. –  birchbark Nov 1 '12 at 14:04

Dangerousprototypes has a generic soldering iron driver, which can run Hakko and Solomon irons (and clones). Since it is open source, it can be easily modified to handle such temperature ranges (it doesn't specify the lower end of the range). All-through-hole PCBs are available for $7. - my question is whether it's possible without programming a chip to modify this. like, with the hakko unit is it possible to add a resistor or something in line with the thermocouple to change it's reading to over-report, or something along those lines, i have no interest in building my own control unit, especially when there are already temperature controllers available worse case that i could route the soldering iron through. – birchbark Nov 2 '12 at 23:16 the dangerousprototypes i believe is far beyond my current (or desired) skill level. what's the advantage of the dangerousprototypes system over a generic PID controller (such as those available on ebay for$20-50) which accepts a variety of thermocouple types and has a broad temp range, etc (such as: ebay.com/itm/… ) –  birchbark Nov 3 '12 at 1:55
The DP one already is able to handle the high current for the soldering iron (the ebay controller needs an external relay for that). Also, the DP controller works not only with thermocouples, but also with PTC (which is used by the Hakko irons). It also has the proper connectors (since the sensor is integrated into the iron itself). Otherwise, it is just a PID temperature controller - but one tailored for a specific use case. –  hli Nov 3 '12 at 19:57
Thanks for specifying, I think what I'm going with at this point is something like that ebay controller, a SSR, a cheap soldering iron, and soldering a thermocouple to the shaft and coating it with silicone (which I have on hand cause it's a moldmaking material). Silicone should insulate it so it can be held by the shaft (more useful for my purposes). I wanted to do the hakko or hakko-clones, but, the tip connection type doesn't allow for easy extension of my custom sculpture knife tips. Cheap soldering irons with screw in or set-screw tips accept custom forged spatula tips better. –  birchbark Nov 4 '12 at 18:33