Suppose I wanted to heat a large aluminum disk with joule heating. I would use one of its flat faces, which has a radius of about a foot (30cm, SA = 0.28 sq m) and enough resistors to dissipate 400W of energy.
If I use 12V across a circuit:
P = V^2/R
P = 320W
V = 12V
R = 0.45 ohms
and the current for such a circuit would be I = V/R = 12/0.45 =~ 27 A (which seems very high)
Is this correct? Is this kind of set up "safe"?
And if you are interested:
If you were to build this circuit, how would you arrange resistors of any R value while:
- Distributing the heat across a large (1ft radius) surface
- Remaining under 100W per resistor
- Maintaining R=.45 ohm total circuit resistance as closely as possible
Here is one attempt of mine, using 10 parallel 4ohm resistors (.4 ohm circuit resistance):
If you think it is safe/worthwhile, I am open to setups with higher voltage, but for some reason 12v seems to be the standard.
Also if I wanted to use PWM (DC) to control the output of this circuit, what would be the cheapest and most efficient way to set that up with Arduino?
My disk is about 10.8 kg with specific heat capacity (Al) = 0.9 J/gC
So I chose 320W because this would allow me to heat by 10 deg C every 5 min:
0.9*10800*10/320 =~ 300 sec = 5 min