42C Resistor by 9V batteries

[whiskeysausage]

Hi guys and gals!
This question requires a very specific solution, and I am all thumbs.

The situation: I need to find a cylindrical resistor that heats up to and stays at 42 C +/- 1 C for 15minutes +/- 1 minute, powered by 4 to 6 9V batteries (wired in any way), and are expected/allowed to be fully drained by the end of the 15minutes.

What type of resistor would allow this? Is this even possible? Theoretically or practically?

Many thanks in advance! Any answers would get me closer to a solution.

Very Respectively,

Whiskey Sausage

 

[KerimF]

What do you have in mind as a control to maintain the 42 C ?

 

[whiskeysausage]

No idea. What do I need, what would you suggest? Simplicity is the key.

 

[KerimF]

I tried to mention that heating a resistor is the simplest part in your project while the part that has to maintain its temperature at a certain value as 42 C is indeed the whole project.

 

[whiskeysausage]

Good point. Do you have any idea what type of resistor would get me closest and quickest to the desired temp? And how would I best control the temp?

 

[KerimF]

If the size of the resistor is not important, the 400mW or 500mW type could be a practical choice, it doesn't need a lot of power hence energy during the 15 minutes (I think the SMD resistors are too small to be considered here).

Added:
Sorry I couldn't get which battery you prefer to use.
Will this battery be used for the whole circuit or just to heat the resistor?

 

[whiskeysausage]

The only 400/500mw resistors I found were tiny. I'm in search of something 5-6inches long by 3/4 inches in diameter. Would a heating coil work instead?

 

[KerimF]

I see, it will be a sort of a regulated mini-heater. I think a heating coil (using a wire that has a relatively high resistivity per inch) should work.

Since the coil will have a fixed resistance, the voltage on it should be made variable, usually by PWM (Pulse Width Modulation).

 

[whiskeysausage]

So I should connect the 6 9V's to a heating coil, and throw a regulator in the middle to keep it at 42C +/- 1C. Is there anywhere I could get an off the shelf heating coil/regulator?