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Topic starter
2023-03-08 12:46 pm
I was watching a video where a guy builds a reflow hot plate for SMD soldering using an old clothes iron as heat source. Managed to find a very old clothes iron I must have gotten from my mom or something? It was made in West Germany, so yeah, it was very old.
After opening it I looked at the temperature knob thingy that you turn to increace or decrease the heat. But I can't figure out how it is working. I've never seen anything like it before. Here's a video I took where you can see it in action.
An old iron made in West Germany
Anybody here that can explain how this thing works?
2023-03-08 2:03 pm
@apeshaft The knob bends the bimetallic strip so more or less time is required for the bimetallic strip to open/close. More time to open means the sole plate gets hotter.
First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, and 360, fairly knowledge in PC plus numerous MPU's and MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
Sure you can learn to be a programmer, it will take the same amount of time for me to learn to be a Doctor.
Apeshaft reacted
Topic starter
2023-03-09 9:03 am
@zander Is this technology that is still in use today? My iron must have been made back in the 70's and things might have advanced a bit since then? This is the guys Reflow Hotplate Version 2.
Could be an interesting project?
2023-03-09 12:37 pm
Hi @apeshaft,
Ron (@zander) is correct on his description of a thermostat based on a bimetallic strip, the rotary knob being on a screw thread which changes the amount the strip has to bend to 'flip' the contacts from closed to open.
Whilst it is a while since I last disassmbled an iron, so far as I know the principle is still in current production. It is cheap to make, and whilst its temperature control is far from precise, especially during the first few minutes from power on, it is "good enough" for that application.
The bimetallic strip style thermostat is used in several kitchen appliances, for example, the automatic switch off for electric kettles trips when the steam fom the boiling water heats the strip sufficiently. Obviously there is no need for a manual temperature adjustment in this case.
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As for the reflow design in the video you referenced, whilst the overall project is interesting, I would strongly recommend anyone contemplating a project using a metallic hotplate, powered by mains power (110-240Vac), ensures that all metallic surfaces of the plate are connected to the protective earth or ground, so that it cannot become 'live' if the insulation inside the plate starts to fail. The video shows the incoming mains cable has only two cores (live and neutral), so clearly the presenter has not considered that it has exposed metal surfaces with only a single layer of insulation from the mains power.
In addition, I personally would recommend that the power to the unit is protected by a Residual Current Detector (RCD) based trip that will disconnect the power if it detects some of the power is flowing to earth. (You might have such a trip for mains powered garden tools, to break the circuit if the cable insulation becomes cut or damaged.) It is common for the insulation of heating elements with a metal covering, to progressively fail with age and heating cycles. Using an RCD increases the chance of detecting this failure at an early stage, before more dramatic and dangerous symptoms appear. Your house wiring distribution panel may provide this level of protection, but unless you are sure it does, and is recently tested, a specific trip may be a good idea.
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Best wishes and stay safe, Dave
Ron reacted
2023-03-09 1:25 pm
@apeshaft I am an old Tube guy, this is all new to me.
First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, and 360, fairly knowledge in PC plus numerous MPU's and MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
Sure you can learn to be a programmer, it will take the same amount of time for me to learn to be a Doctor.
Topic starter
2023-03-24 6:40 pm
I decided that the West German Made Iron was a bit to strange for me. Instead I got another much cooler, but also much hotter since it ain't broken. It's made in Sweden and it's an "Andersson". It's not THE "Mr. Andersson", just Andersson. I'll keep you informed if this Iron is less centered around The Blair Witch Project Tech Tree and not powered by words written in the Necronmicon.
