I have 2 meters, 32wg, 19 ohm per meter. NIchrome wire
I want to calulate what amps and volts i need so 2 meters of nichrome heats to 35 celsius.
How can i calulate this and what formula do i need to use.
Answer
Best source of information would be in the datasheet for your wire.
Barring that, there are some common things that would help. Current is based on \$I = V/R\$. Given that you provide 19Ω per meter, and you have 2 meters, that's 38Ω. But that is it's room temperature (Typically ~21°C). As temperature rises, the resistance rises. But let's work with that.
Consider \$I = \dfrac{V}{38}\$.
And you want a ~14°C rise. Most of the time, standard tables show extremely high temperature rises.
So these can be used for a reference. A 32 awg straight wire raised from (Room Temperature 70°f) 20°c to 400°f (204°c) takes 680mA. 1000°f (538°c) is twice the current. And 2000°F (1093°c) is twice that again. So current is doubled for roughly slightly 2.6 the temperature but resistance rises with temperature, so quadruple the current for five times the temperature. We can assume that the inverse is true. At lower temperatures, less current gives higher temperature rises.
With your 38Ω piece of wire (Straightened out, not coiled) to 400°F, that is ~26V (not including resistance changes). (0.68 = 26V / 38Ω). 35°c is 95°F. That's slightly more than a fourth of 400°F. So try cutting the current to a 5th of that. 0.68 / 5 = 0.136.
$$ V = I \cdot R $$
$$ V = 0.136 \cdot 38 = 5.168V $$
Try 5v. You should get a rise to less than 100 degrees fahrenheit, roughly less than 37°c. Anything else would require a calibrated temperature sensor and testing. Reduce current by half for coiled wire. And carefully check resistance when the wire is at the temperature you want (after you disconnect the power)
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