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I'm trying to make a very small (3x3 cm or less) cup or surface that will heat to around 200C. The surface needs to be dry and I only care about heating the surface and not any particular volume of air around it. Ideally this would be on fairly low voltage (nothing more than a 9V hopefully, or even possibly on a USB connection) so it could be semi-portable.

I don't have a lot experience with heating elements, so I'm not sure of the best way to do this. Is this even a feasible project? If so, are there any out of the box things I can buy that will do this? Or will I have to resort to something like fixing some nichrome or heating pads to ceramic and doing a lot of testing?

Additionally, are there any recommended ways of controlling the temperature of the surface? I was thinking of making some kind of PID control with a temperature sensor, but I'm sure there's a simpler and safer way.

Thanks for your help!

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    \$\begingroup\$ How do you plan on dealing with edge effects? Or perhaps it's not important to you that the edges and the center are at the same temperature? Just curious. \$\endgroup\$
    – jonk
    Jan 11 '20 at 6:28
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    \$\begingroup\$ The power that the supply needs to deliver is equal to the heat loss to the outside world. If it is a surface in open air, the heat loss may be considerable. If it is a surface inside an insulated box, then the heat loss will be much less. \$\endgroup\$
    – mkeith
    Jan 11 '20 at 6:33
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    \$\begingroup\$ Kip, you really need to open your hand and let us see what you are holding tight against our view. What are you really trying to achieve? It will go a LONG way in saving us a lot of time if you'd just get at the nub of it and let us know your actual goal. Obfuscation isn't a good idea, right now. Open up. Let us see what you've got going on. \$\endgroup\$
    – jonk
    Jan 11 '20 at 6:36
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    \$\begingroup\$ @Maple I think the OP needs to open the hand. I'm not interested, otherwise. \$\endgroup\$
    – jonk
    Jan 11 '20 at 7:54
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    \$\begingroup\$ @mkeith they use nickel, titanium and stainless steel wires \$\endgroup\$
    – Maple
    Jan 12 '20 at 1:00
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I am not familiar with that kind of devices but I don't think they are much different from e-cigarettes. Specifically:

  • They probably do not keep heat constant, but rather activate it when necessary, either manually or by air flow detection;
  • The temperature is sensed by measuring current and voltage and using thermal coefficient of the heating element material. That is the reason you have to configure it in the vaping mod when you change a coil;
  • The temperature control is usually quite primitive, no PID, just plain current limiting when coil reaches target temperature. Something like P-only control;
  • A single lithium battery with high current rating is typically used. This simplifies charging from USB port, but requires reliable low voltage and over current cut-offs;

So, using off shelf vaping mod as a base of your device could be a good starting point. You just have to figure how to replace vaping coil with suitable heating chamber. For example machine it from aluminum or stainless steel, wrap with something like polyimide film, then wrap coil around it and enclose everything into protective case.

Or you can find old or broken commercial IQOS and see how it is made. In any case some (probably a lot) of testing would be involved in project like this. The trick is to maximize area of contact with hot surface and minimize heat loss to the outside.

Finally, if you allow me going a little off-topic - whatever the delivery method is, the end result is not good for you.

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