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Some final notes

If you decide to build this schematic too but are afraid to void the warrantee on your precious Weller, keep in mind: the schematic is connected in parallel with the soldering iron, so it should be possible to make a male-and-female-connector construct to go between the soldering iron and the station itself. If the circuit is connected to that, no modifications to the iron or station themselves are necessary.

If you have trouble getting a 24V zener: you can put zeners in series, so 2X12V will work too. If you can't get any zeners at all, it's possible to substitute the zener for a 22K-resistor, but the circuit will get a lot more difficult to calibrate.

And one final warning, if you decide to open your soldering station: be careful, there's mains voltage in there which can give you a nasty shock. You might want to use a different soldering iron to connect the schematic to the transformer, so you can leave the station unplugged. Offcourse, I'm not responsible for whatever you do to yourself or anything else after reading this article.

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19 comments

giancarlo wrote at 8 Feb 2016, 23.52:

To save money I bought only the stylus Weller and the part feeding the I built it. The transformer when supplies from the secondary, buzzes slightly. So my operating monitor is sound. Congratulations for the idea.

Michael Anton wrote at 14 Oct 2014, 0.59:

You could simplify this slightly by using the first transistor to short out the LED when it is turned on. This eliminates one transistor, and a resistor.

paul wrote at 10 Apr 2013, 10.35:

hi excellent idea im going to give it a try thanks regards paul

wibaje wrote at 18 Mar 2011, 23.19:

I'm curious why u didn't use a series resistor to measure the current. The Current would be around 2 amps(50W/24V). A resistor of 0.1 Ohm would give a voltage drop of 0.2 V, large enough to measure with a uC and small enough not to impair the heating of the tip.

paradox wrote at 28 Aug 2010, 7.33:

Opps forgot you will still need to rectify with the diode and capacitor voltage divider *should = 6.8 at 30v input to calculate r1 and r2 6.8 = (r2/(r2+r1))*30 voltage divider using zener *reference voltage to calculate r3 -29 + (.01)R3 + 6.8 = 0 lm339 2.4k Ohm resistor and led This is commonly used as a low voltage battery warning

paradox wrote at 28 Aug 2010, 7.20:

You can easily use a voltage divider and comparator to check if the voltage is at a certain level takes about 7-8 parts depending how accurate you want it reference voltage on the inverting input using a zener diode then a voltage divider to the inverting and voila

bob wrote at 14 Dec 2008, 14.26:

My complements to you and your website. After reading this project and the "Electronic minimalism" section, the following thoughts occurred. Why not just put eleven cheap red LEDs and a low value resistor in series with the 24v supply? No calibration pot, transistors, etc. It seems to me the (approx.) 2.1v reverse voltage per red LED, multiplied by 11 would give the stack a cut-off of around 23v. When the supply voltage was at 23v, you'd get 20 ma current flow, if below 23v, insignificant current flow and negligible illumination. Of course, if the supply voltage was significantly above 23v, the overcurrent would burn out at least one LED. I haven't tried this myself, but if tweaking was necessary, a few regular small signal diodes with a reverse voltage of 0.7v could be added (and/or the one of the 11 red LEDs removed) from the series string to get the setpoint just right. Or use a combination of zeners plus one LED that adds up to the cut-off voltage? Could get it down to only 2 or 3 components that way.

Kurt wrote at 19 Nov 2008, 1.10:

The noninvasive solution is simply to monitor the current at the wall power plug. (I hope HTML PRE tags work here.) <pre> 120V |-------------------|<|-----------------| hot | rectifier diodes | hot in |-------|>|-----|>|-----|>|-----|>|-----| out o----| |-----> |------------|>|----////------------| to LED 100 ohm weller neutral o---------------------------------------------------> </pre>

dan wrote at 7 Oct 2008, 16.28:

i have same problem as tony, but mine never blew a fuse. Is it the heater element/coil? Please advise.

richard wrote at 29 Apr 2008, 16.50:

Do you not have problems with changes in line voltage affecting this since it simply detects a voltage shift on the output? its not uncommon to have a + or - 10% swing depending on what else is on and the time of day.

G. Beat wrote at 28 Feb 2008, 4.16:

Tony - I will answer with USA/North America part numbers, ut they may be the same for UK style Weller "TCP" irons. SW60 - Magnistat switch (Magnetic switch - Carl Weller's original patent). Works with Weller PT tips (which have a specific ferrous plug at end of tip) -- that is your temperature control -- using the "Curie effect" Heater - EC234 for plug-in and TC-208 for wired in versions. This is dependent upon your specific handle and age/version. VERY EASY to repair these!!! Here is the WTCPS - EU/UK version http://bama.edebris.com/manuals/weller/wtcps_eu/ Rest of N. American manuals on BAMA http://bama.edebris.com/manuals/weller/ Try this web page for European support: http://www.cooperhandtools.com/europe/spare_parts/weller/index.htm http://www.cooperhandtools.com/europe/electronics_products/weller/index.htm Contact: Stephan Hofmann Tel.: +49 (0) 7143 580 145 Global Product Manager Electronic Fax: +49 (0) 7143 580 113

Heinz wrote at 2 Feb 2008, 21.36:

I have the idea of a led control since a few month and now I find a solution here. Great! My thougts in the past were to use a reed contact and made few turns around it. So the magnetic field will close the contact and drive a led. But the problem is the 50 Hz! Now I decide to build your schematic...

Tony wrote at 15 Jan 2008, 14.25:

Just found and bookmarked your site through google and found the weller soldering station project to be very cool and will build it when I resolve my current problem. So I am sure this probably not the right forum to ask for help but you seem to be very knowledgable about Weller Equipment so I am hoping that you may be able to help me out with my weller wtcp series with a tc201 pencil. I have had it about 15 or so years and the tip finally fried. I got a replacement at Fryâs and all was good until yesterday, I was working on a project and the light was still on on the base unit but the pencil had gone cold. I opened up the base and saw that the 3 amp fuse was blown. I replaced it with one from Radio Shack and it would still not heat up. So after scouring the web for info I know have 4 questions: 1) What VAC voltages should I see at the connectors 3 pins on the base unit to determine if all is well there? 2) Is it common to replace just the heating element for $20. + versus the $70-$90 for the entire replacement pencil? and 3) What exactly is the capacitor and other mystery "Magnetstat" & spring components attached below the heating element and are those subject to failure and replacement as well? 4)That component moves but with lots of resistance. How exactly does should that component work?Thanks for your interest and time regarding my problem. BTW you have a great site, keep those cards and letters coming!! Leave a Reply

Ben wrote at 20 Nov 2007, 5.49:

I love it simple but elegent.

K-Ray wrote at 6 Jul 2007, 18.53:

Very nice feature! I don't know if my boss would like me tampering his solderstations, but I'm gonna try it anyway.

Ryan wrote at 12 Jun 2007, 3.03:

I have already begun! ty!

Johan wrote at 20 May 2007, 16.08:

Nice! A good solution to an irritating problem.

Dan wrote at 18 May 2007, 1.30:

I love the last bit; "You might want to use a different soldering iron to connect the schematic to the transformer, so you can leave the station unplugged" I did not clue in until I re-read it. I do not have the same model as you, but I was inspired and will do something similiar. I will just add two wires coming off the heat magnetic detector already there ;)

Techyguru wrote at 18 May 2007, 1.29:

Sweet and simple. I like it

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