I have a heating element commonly used for electric stove ,its 1500 watts 230V what i need is reduce the size to maximum because i cant fix it in my project which don't have enough space to fix the entire element and i dont need very high temperature too (a photo of element is attached here for reference),So suggest me some ideas to reduce the length.

What my opinion is reduce the size by reducing the length and applying a 12v source but i use a small power source 12v-1.5A only

  1. if i need to bring the current below 1.5A in 12v so i need to use 1/2 of total length of element(approx only).but still longer so can i use a resistor in series?

  2. what watts rated should be used?

  3. is there any other method of heating using small area and little power,which should be durable.

  4. If resistors are used for heating is it a good method? I believe that resistors using as heat source is not the right method as it is not a device designed for heating?enter image description here

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    \$\begingroup\$ Ignoring the rest of your question: Why and what do you want to heat? \$\endgroup\$ – Rev1.0 Mar 4 '18 at 12:39
  • \$\begingroup\$ The difference between a resistor and a heating element is an explicit heating element is rated for higher temperatures. That's it. If you stay within the temperature limits of the resistor, there's no reason not using a resistor. You may even use a bipolar transistor as a heating element. The latter has the advantage these are built for heatsinks already. \$\endgroup\$ – Janka Mar 4 '18 at 12:48
  • \$\begingroup\$ the application is for heating air near 50 degree C,in a closed box \$\endgroup\$ – Eng. Jamshid Mar 4 '18 at 13:04
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    \$\begingroup\$ well, an airplane is a closed box, too. So, how much power do you need? How fast do you need to heat up how much air? \$\endgroup\$ – Marcus Müller Mar 4 '18 at 13:18
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    \$\begingroup\$ The physical thermal control specs are not well defined. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 4 '18 at 13:30

1500W 230V => 6.5A and 35 ohms

12V 1.5A => 8 ohms

If it's a 35 ohms resistor and you cut it at 8/35 = 0.23 times its length then you'll get 8 ohms and it'll work on 12V.

It will only heat 18W however, so you decide if this will work in your application.

The choice of heating element depends on what you want to heat also (if it's water, you must use something waterproof...)

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  • \$\begingroup\$ It's capable, ignoring edge effects for now, of 6.25 A. Dissipation wise. So 2 ohms. That's 1/20th the length. And 78 watts. So that would be the maximum safe wattage at 12V, I think. Or do I make a mistake here assuming 6.5 A is supportable regardless of cut length? \$\endgroup\$ – jonk Mar 4 '18 at 13:08
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    \$\begingroup\$ OP says 1500W at 230V not 12V so it will be 35 ohms ;) \$\endgroup\$ – bobflux Mar 4 '18 at 13:14
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    \$\begingroup\$ I also compute 35.25 ohms for the entire length. I'm merely suggesting that it can support 6.5 A over its entire length and therefore can support 6.5 A over any desired length. Cutting it still shorter than you suggest may still be fine. And 12 V can still be applied on the shorter length. Not so? Just would require more current compliance. \$\endgroup\$ – jonk Mar 4 '18 at 13:21
  • \$\begingroup\$ OK! yes, you're right. But OP wants to use it with 12V 1.5A supply (no idea why) so I went with that. \$\endgroup\$ – bobflux Mar 4 '18 at 13:24
  • \$\begingroup\$ Just thought the OP might not know of that approach and that it wouldn't hurt to suggest another added thought about it. We agree, I guess, about the rest. \$\endgroup\$ – jonk Mar 4 '18 at 13:26

Ceramic R raised well above PCB and good clearance is certainly viable solution but convection flow and variation in T is unknown. I have even used SMT R with foam insulation and flex copper shield for Xtal tests.

Heating air by convection inside a box with no flow may not be very accurate, but then you didn't specify details and specs for error.

like Ohm's Law for heat.

Pd* Rth = T rise ( static ) for Rth, thermal resistance ['C/W]

For dynamic temp you need, rate of change of 'C/W , outside Ambient range (and anything else, temp gradient inside , overshoot error, etc) then initial power and steady state power can be selected.

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