How do I generate less than 0.05 V to heat a NiCr wire, or otherwise prevent the wire from consuming too much power?
I want to heat a length of Nichrome wire in order to cut through very thin pieces of nylon -- basically a "hot knife". I estimate the wire will be about 6 mm long. In order to provide some thermal mass and also prevent the Nichrome from being too weak to cut, I plan on a 16 gauge Nichrome wire, which has a resistance of ~0.26 ohms / foot, which is 0.0051 ohms of resistance for 6 mm. According to this calculator to produce 650 F I need 0.44 W.
0.005 ohms at 12 V is ~28.8 kW watts, which is... more.
How can I power the wire which has so little resistance without generating too much power? From my understanding:
- Add a resistor will just end up generating more heat from the resistor than the NiCr wire.
- I could regulate the voltage down to a lower voltage, but it seems that voltage regulators only go down to about 1.8 V, which still produces 650 W.
- I could run a PWM. If I combine a 1% duty cycle with a 1.8 V regulator then I'm at ~6.5 W, which is still much too high. Also, many PWMs and voltage regulators can't handle the ~10 A of current at that voltage.
- I could get smaller NiCr wire (higher gauges) and/or lengthen it to increase the resistance. Even wires as small as 32 AWG still require less than 0.2 V at 6 mm and I'm concerned about the wire not being sturdy enough. I could run the wire back-and-forth a few times (say 10 times for 60 mm in length) but then I have problems keeping the wires from touching when trying to concentrate them on the edge of the "hot knife".