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I'm trying to make a vaporizer pipe as a hobby project. The idea is that when you inhale from it, air passes by a cartridge heater and then goes through some "herbs". A thermocouple is used to measure the temperature of the heating cartridge. A microcontroller will read out the thermocouple via the MAX6675 chip and control the power of the cartridge heater using PWM via a MOSFET, in order to keep the temperature stable at a desired value.

I bought:

  • Cartridge heater Watlow C1A-9602: 24 V, 30 W, 1/8" diameter, 1" length, alloy 800 sheath
  • Thermocouple Watlow 20CKFUA012A: Calibration type K, 1/8" diameter, 1/2" length, stainless steel 304 sheath

Can I solder the cartridge heater and the thermocouple together? Then heat will easily flow from the heater to the thermocouple and I get a very accurate and consistent temperature reading.

Cartridge heater and thermocouple

The solder must be able to withstand 250 °C (482 °F) without causing any possible problems for the user, since the user will breath the air that flows next to the solder.

What solder could I use for this? Or is this a bad idea? I looked at solder alloys on Wikipedia, but there are just too many options. Perhaps I could use the cartridge heater itself to melt the solder.

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  • \$\begingroup\$ don't you want to measure the temperature of the heated air instead? \$\endgroup\$
    – jsotola
    Feb 15, 2023 at 1:29
  • \$\begingroup\$ The obvious problem with soldering is that the solder will melt at less than 250 degrees C. Although Wikipedia has a long list, there are just a few types of solder commonly used in electronics; I think mostly just 60/40 lead (or 63/37 for some people but that's not a lot different) or a handful of different lead-free alloys that are also pretty similar to each other. \$\endgroup\$ Feb 15, 2023 at 1:39
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    \$\begingroup\$ (I edited the comment) You would be looking for some special type of solder to withstand this. For a high-temperature permanent metal-to-metal attachment you could consider brazing or welding. Or you could just wrap some wire around both to hold them together, although the thermal contact won't be as good. \$\endgroup\$ Feb 15, 2023 at 1:42
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    \$\begingroup\$ I think you will want to insert the heater into a hole in some kind of heatsink, which helps transfer the heat to the air. Then you can put the thermocouple in another hole in the same heatsink \$\endgroup\$ Feb 15, 2023 at 1:44
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    \$\begingroup\$ Silver solder or (better) weld. You might want to avoid anything with cadmium in it, if those solders are still sold in your region. \$\endgroup\$ Feb 15, 2023 at 2:21

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It's best to use a "copper" block with 1/8 inch holes, precisely drilled or made by CNC (by some blokes CNC shop) and clamp these devices with "tiny" headless screws.

https://www.wikihow.com/Solder-Stainless-Steel

Unlike other metals, stainless steel is very difficult to solder. It has a thick oxide layer that prevents melted solder from sticking to its surface.

using a burner around wires probably not a good idea, either.

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    \$\begingroup\$ Any reason you put "copper" in quotes? \$\endgroup\$
    – Paul
    Feb 15, 2023 at 16:50
  • \$\begingroup\$ @Paul well copper is better than aluminum and other materials. He probably want the best results, not sure if there is anything better than copper. \$\endgroup\$ Feb 15, 2023 at 17:54
  • \$\begingroup\$ Alright, yeah, seems like a good idea. \$\endgroup\$
    – Paul
    Feb 16, 2023 at 11:49

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