Teardown of a thermally controlled soldering iron element.
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- Опубликовано: 4 мар 2014
- This is what's inside a typical 24V 50W soldering iron heating element. I actually thought it was going to be simpler than this, but it's quite impressively engineered.
The construction is basically a ceramic core and outer ceramic sleeve. The core has three small holes up its full length and these are used to insulate the wires for the thermal sensor and heating element from each other. The thermal sensor is a common thermocouple composed of two dissimilar metals fused together at the tip of the iron. These generate a small voltage that relates directly to the tip temperature. I estimate that at a typical iron temperature of 350 degrees the sensor will produce a voltage of about 14mV which is monitored by an op-amp in the controller.
The heating element itself is wound round a short section of the inner ceramic core near the tip and terminated by simply running the same resistance wire to the connection PCB in the soldering irons handle, but also running it with a compatible but much lower resistance wire that is twisted along the full length that isn't intended to heat up. This seems to be a common way to terminate heater wires, since it provides a low stress connection.
The inner core with heating element and thermocouple are then slid into an outer ceramic tube and sealed at both ends with a ceramic paste. The protruding wires are sleeved with a high temperature sleeve and the ceramic paste is also used to glue them in position.
Although the irons element is rated at 24V the transformer winding that feeds it is rated over 30V to allow for losses over the opto-isolated triac that switches it and the resistance of the thin cable to the iron itself. 
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I'm 9 years behind, but catching up. Keep them coming...
Incredible that clive is reading comments on these old videos!
Best... Soldering iron breakdown... Ever. Thanks so much for sharing your findings.
Great video. I had a Dick Smith soldering iron control circuit fail about 12 years ago. (no spare parts available) Now running it on a small variac at 170 Volts, ramp it up if needed for more temperature. Works fine and does the job.
Thank you for this video it helped me a bunch👍
Thank you. I now have the confidence to buy this brand. I have always been a gear snob. Can't bear the price anymore.
I've gone through three soldering irons one from from walmart, next time I buy one i'm getting the protection on it. I've made two "apocalypse style" soldering irons from the two that died on me. They are basically cordless and you heat them to cherry red with a torch and it does work but doesn't last long.
I've torn the two irons down and found a very thin wire which serves as the heating element with about 120 turns of wire connected to another set of twisted wire which runs to the electrical connections. The iron tested open for continuity.
Thanks 👍
Took my Hakko iron apart just know. It's nearly identical. Kind of wishing I'd gone for something cheaper with more features.
Can you tell me where to find an element that is 23 volts and 70 watts, I can’t for the life of me find one that will fit my well let Wep 70 handle.
im confused, does the heating element need only the connection positive. or you have to put the negative ans positive between the heating terminal?
Interesting video
Do you have any info or knowledge on the composite soldering tip with Built-in heating element !
Very clever!
Hi, very interesting video. Clear, no background music and very illustrative, thanks for sharing. I don´t have the schematics so I would like to confirm: in my iron element there´s a fifth cable, conected to a spring which sorrounds the ceramic package, is that an earth connection ? Regards
Yes. That's probably the ground connection.
I have one of these china specials and my issue is the tips don't seem to make good contact with the heater... and by "good" I of course mean... none... Measuring it the tip of the heater is a good 4 or 5 mm from the end of the tip when assembled and with a fraction of a millimeter gap all around, I found I had to pack in some tin foil, and wrap the heater with foil also or else the tip itself would barely heat up.
This is using the tips provided and I can't possibly imagine this is normal. Since the issue was first noticed the ceramic had become black and almost like charcoal, I assumed this is because it had over heated trying to get the tip upto temperature, and just today became so brittle it snapped off while trying to swap tips.
So... is this the heaters fault somehow being too short and narrow, or the tips fault for being too wide and long... or is it the usual case of "who knows, its a cheapo chinas job, you're lucky it worked at all"?
kal9001 I’ve ran into the same issue. I’ve altered the circuit board that the base of the heating element sits on either by cutting a bit off or adding a bit with cardboard and kapton tape to get the heating element to touch whatever tip I’m using.
How does the aluminum foil trick work?
How exactly is the temperature controlled? Is there a constant 24v that is pulse controlled or is the 24vac altered like a dimmer?
The 24V is usually AC controlled by a triac and pulsed on and off as needed.
I have a basic 60W soldering iron and the element sometimes only lasts a few minutes.
What is going wrong here? Surely elements should last longer.
Is it actually rated for your supply voltage?
can you offer some advice on what type of element would i need to get a low temp of 90 to 100 degrees. possibly something i could set up to be battery operated. thank you
The type of heater depends on what you are heating. You get USB powered heater pads and you get submersible 12V cup heaters.
I have a problem with my rework station, 907 not heating up, I know the iron works, tested with other simillar unit. I am measuring 24v at transformer. somehow the thermocouple is not switching the heater on. thanks for informative video.
Does the display show a temperature if your unit has one?
Not a temperature LCD, (KAWH 852). Led temperature indication. If I heat up the iron in a working station and plug it in the defective one the led give heat/thermostat indication from the thermacouple.No 24v output at the socket pins. regards
Jan van Heerden It must be the control circuitry on the PCB or even a bad connection. Try tracing just the power switching side in the unit.
On the heating element on mine only one end had another wire twisted together and spot welded, the other end it looks spot welded to another wire going to the electrical connection without a twisted connection. Is there a reason only one end is twisted together with another wire and not both?
The wires that were twisted together and welded were probably the thermocouple temperature sensor. Two different alloys that generate a slight voltage that indicates the temperature of the iron tip.
bigclivedotcom I’m referring to 3:42 where you explain that one leg of the heating element has another wire twisted on it but not on the opposite leg
I have a Zeny SMD soldering station, it's a decent station. I ordered a few extra soldering iron, I thought any 5 pin female soldering irons would work, but when they are hooked up to the station, it doesn't detect a temp sensor, it reads 0/1 and the iron gets very hot. Im trying to figure out how to rewire it, or if they where assembled improperly these are cheap irons.
Some systems use a thermistor and others use a thermocouple.
bigclivedotcom and they are not compatible with the same rework station. They. Both have a cermacic heating element. I do see the symbol for resistor on the back of the. Board. I will upload pictures of both iron boards, if you could take a look at them, and tell me if there is any to require this to make it work, I'd appreciate it. Thanks for responding
i66.tinypic.com/2ueof94.jpg
[IMG]i67.tinypic.com/2vll5qh.jpg[/IMG]
i63.tinypic.com/2e57ecj.jpg
i63.tinypic.com/qqpbg6.jpg
Here is an images I puloaded to tinypic, the one on the right is the one that came with my SMD station, works fine. The one on the left the station doesn't detect the temperature, so it goes to max and if I leave it long enough it will burnout the heating element.
Hi what about t12 tips they only have t+ t- and ground and its temperature controlled... how??? someone explain please. thanks
could it also be a bad idea to solder something to the heater of a SOLDERING iron? xD
Boa noite irmã boas esse comentário fosse traduzido em português que em inglês eu não tô entendendo nada
You can't smoke heating elements c'mon
A 24VAC (50W) heater element would require a 110-220VAC to 24VAC power transformer, right? Wouldn't be easier to use a 110-220VAC (60W) heater element instead? (see example: goo.gl/CTEqjb)
Answering myself: yes and no. Yes, we can use a 110-220VAC heater element without using a power transformer (eg. ROHS-936D) when such assembly/device do not use a micro-controller to adjust the temperature with +/- 1C. And NO, we cannot use a 110-220VAC heater element in a micro-controller driven assembly/device when normally we want the micro-controller (which normally works at 5VDC) to adjust the heater temperature.
could it also be a bad idea to solder something to the heater of a SOLDERING IRON? xD