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Coiled heating element 
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#1
Mar1207, 08:22 PM

P: 5

I'm making a coiled heating element from nichrome wire, and I was wondering how the coiling will affect the current. I have values for current needed for straight nichrome wire, but I believe coiling it will change the resistance.
Thanks. 


#2
Mar1207, 09:12 PM

Mentor
P: 7,315

No, go ahead and compute your length then coil it to your needs.



#3
Mar1207, 09:28 PM

Mentor
P: 40,658

Just to add a bit to Integral's correct response. As long as you are using 50/60Hz AC power for the coil, then the inductance of the planar coil structure is negligible for the small number of coil turns that is typical.
If you were making a 100MHz RF heating element, then you would definitely need to include the inductive reactance in your design calculations. Do our comments that make sense and answer your question? Welcome to the PF, BTW. 


#4
Mar1207, 10:39 PM

P: 1,636

Coiled heating element
But a coil would tend to keep the heat generated inside, instead of radiating it back to space. As a result, an increase in surrounding temperature would result in the increase of the coils resistance. But I suppose these effects would be just too negligible.
Just power the coil by a constant current source, that will take of all uncertainties. 


#5
Mar1207, 11:02 PM

Mentor
P: 7,315

The resistance of nichrome does not vary significantly with temperature. In a former job we were worried about that very thing. We cut a long, ~10m, length of nichrome measured its resistance cold, then the current and voltage drop. The resistance remains pretty constant with heating. We then calculated the heat required cut the appropriate length of wire coiled in and poured a refractory cement around the coil to create our own Aluminum melter. We melted a lot of aluminum in that very nicely, it worked as designed with no concerns about the temperature dependence of the resistance.



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