/diy/ - Do It Yourself

>>1727909
Thermal power = electrical power = P.
P = temperature difference / thermal resistance (inside to outside)
resistance per unit length = resistivity / cross-sectional area
R = resistivity * length / area
P = V^2 / R * pwm duty cycle
Hence:
V^2 / R * dc = ∆T / thermal resistance
All in SI units, because all those proportionality constants that inch-standard/imperial needs really drags you down. If you're using a PID and plan to use a low duty-cycle in steady-state then you shouldn't need to worry too much about thermal resistance.

Use https://en.wikipedia.org/wiki/American_wire_gauge or picrel to get the cross-sectional area for your particular awg choice. In your case, 18awg is 0.823mm^2 or 823E-9m^2, and nichrome has a resistivity of ~1E-6 Ωm.

I simply wouldn't trust online calculators for this sort of thing. I'd instead do math in a spreadsheet or python program so I can change initial variables and see how the answer propagates.