This project is build number 2 of a 110v temperature controlled soldering station. It is a follow-up post to the project that I was working on last October.
This version has a couple of improvements over the first build. This new soldering iron is a better unit and was less expensive than the first one.
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A chisel tip plus a selection of other tips was available for this soldering iron instead of being limited to a conical tip only.
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This new soldering iron includes a ground wire which made it possible for a grounded connection.
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Like the first version, a thermocouple was mounted internally inside the soldering iron and the power cord was replaced with a flexible multi-conductor cord and a 4-pin DIN connector.
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The thermocouple was adjusted so that the tip temperature matched the thermocouple reading making it unnecessary to require any temperature offset adjustment in the controller.
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This is an easy project that requires only basic skills to build and it makes a pretty good shop tool. It’s performance is on par with similar commercially available units.
I am working on a project trying to see if it is possible to substitute a MOSFET for an SSR as a means for switching a soldering iron on and off with a PID temperature controller. Please see attached block diagram and partial schematic below:
Edited diagram and the specification - added the LED and resistor Mar 30, 2016 ... [attachment=0]
I want to know is there a way to use a transistor in the circuit to do the switching? When the SSR signal is "on" (Vin ~8v) it needs to open the connection between A and B and switch the load on. When the SSR signal is "off" (V0) it needs to close the connection between A and B and switch the load off.
I breadboarded the circuit and basically used one of the breadboard leads as a switch between A and B. I used an LED and resistor to simulate the load and another LED and resistor connected to the PID controller to simulate the SSR signal. When the connection between "A" and "B" is closed, the LED simulating the SSR blinks on and off in sync with the PID controller. When the connection between "A" and "B" is open (I pull the lead out of one side) the LED simulating the SSR shuts off and the LED simulating the load lights up.
Test board with soldering iron, PID controller, transformer and breadboard: [attachment=2]
Closeup of breadboard next to step down converter / voltage regulator for powering the load LED [attachment=1]
A 110v 60w regular plug-in soldering iron was modified:
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A thermmocouple was placed internally inside the soldering iron and the power cord and AC plug was replaced with a flexible multi-conductor cord:
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A single 4 pin DIN connector was used.
The controller is a simple circuit and was made from a PID temperature controller plus a 25 amp SSR:
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This is a photo of the back of the unit:
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In this photo the temperature is checked with a tip thermometer:
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This is the 3rd version of the same idea - placing a thermocouple inside a regular plug-in soldering iron. The first two versions had gradual improvements but the power cord and thermocouple cable together were very stiff and hard to work with. This version solves that problem.
This is an easy project and it makes a pretty good shop tool. It is on par with similar units that are commercially available.
This particular soldering iron was a little slow to heat up - probably because of the massive tip. There are similar models that I think may heat up faster. I'm working on one now, plus it has a better tip selection. I will post updates if anyone is interested.
I have made a new YouTube video and a blog post with a second version of how to modify an ordinary plugin soldering iron to work with a PID temperature controller. This new version has some improvements since the first version back in April, 2015. The soldering iron in this new version gets hotter and heats up faster than the first one. It also uses a different PID controller that is capable of higher temperatures plus it uses an SSR instead of a built in relay.
Like the first version, a K-type thermocouple was mounted internally inside the soldering iron at the back of the heating element. Mounting the thermocouple internally has the advantage that it is out of the way. The video shows the unit being tested with a range of temperatures at 200°C, 250°C, 300°C and 350°C. A tip thermometer was used to compare the temperature of the soldering iron tip with the temperature controller.
The results were promising. The tip temperature coincided with the internal temperature pretty closely and varied by only a few degrees in most cases. Overall, it seemed like the thermocouple would register the temperature change a little bit faster than the soldering tip but after a few seconds the tip temperature would catch up with the thermocouple.
This project is for a temperature controlled soldering station built from off the shelf parts.
Other than the soldering iron, the circuit uses only three main components - a PID temperature controller, an SSR (solid state relay) plus a transformer.
It works pretty decent considering it was just basically assembled from stock parts.
[attachment=3] This is the schematic.
[attachment=5] The unit uses a 24 volt, 48 watt Solomon replacement iron for an SL-30 soldering station. Basically it should work with any 24 volt soldering iron with a K-type thermocouple sensor.
The transformer would have to handle 2 amps because that's the current that a 24V, 48W soldering iron would require. I experimented with a few different ones.
First I tried two inexpensive 40VA transformers in parallel. One 40VA transformer was only rated at 1.67 amps so I thought I would try parallel transformers to see if I could get double the current capacity. No such luck! One transformer got hot and the other one stayed cool. That was a bust.
The next transformer I experimented with was a 50VA model which was rated at 2.08 amps. I thought that it would work because the soldering iron would only draw 2 amps. But the secondary voltage under load on the 50VA transformer was very low - only 20.0 - 20.1 volts. That put the current at 2.39 - 2.4 amps. I blew out the transformer!
I found an inexpensive 75VA transformer. I was also experimenting with coupling the SSR to the primary. The SSR specification had a voltage drop of 1.6 volts and as a result, the voltage was lower when the SSR was coupled to the secondary. Coupling it to the primary also stressed out the transformer. I settled on coupling the SSR to the secondary.
[attachment=4] The enclosure cutouts were drilled and shaped and then the parts were fitted into the enclosure before final assembly.
[attachment=2] The PID controller was inserted into the cutout and pressed in all the way until the tabs clicked into position.
For people who are interested in soldering irons and temperature control, I have put together a circuit for controlling the temperature of a regular plug-in soldering iron in a different way than usual.
A good quality soldering iron with a temperature sensor has a controller that sends power to the unit in long or short intervals at full power. I got the idea that maybe I could do something similar with a regular plug-in soldering iron without a sensor.
Instead of using a dimmer to send a steady flow of power at constant rate I used a cycle timer to send power to the soldering iron at full power using pulses at precisely timed intervals.
It is only a test board but the results were very encouraging so I made a video and a blog post with all the details here:
For those who are interested in soldering iron temperature control I have posted a video and a blog post with complete details on how to modify an ordinary plugin soldering iron to work with a digital temperature controller. A thermocouple was mounted internally inside the soldering iron so it is out of the way. The idea was to find the "sweet spot" at the back of the heating unit inside the soldering iron where the temperature would match up with the temperature of the soldering iron tip.
The unit was tested on a range of temperatures at 200°C, 250°C, 300°C and 350°C to see if the tip temperature would coincide with the internal temperature as the soldering iron heated up. The results were encouraging. The tip temperature varied by only a few degrees in most cases and even coincided with the internal temperature a few times.
I also have a short video without any narration showing how to adjust the thermocouple to the tip temperature.
A PID controller was used for the test but it was slow. I am looking for a better controller that will achieve the temperature settings faster. For anyone who has some ideas on this please post your comments.
After 24 hours if the new topic is approved, I will post the links to the videos and the blog post.
