Heating Nichrome Wire with Arduino Uno

Using Arduino Project Guidance
1

Hello,
I am currently working on a project in which I need to heat up a heating element that will fit within a pair of full seal goggles. For this idea, I am using 20g nichrome wire. While this may seem simple, I need to create a toggle button circuit that will control the settings of the nichrome wire (ex. press once, it will run current for 2 seconds, then off for 8; press it again, it will run current for 2 seconds, the off for 3, etc).

Question 1: Will the Arduino Uno itself be enough to heat up the wire to about 35 degrees Celsius?

Question 2: My current code looks like the excerpt below, taken from another, similar project online. Will it work for my purposes?

const int ledPin = 12;
const int buttonPin = 2;
int state = -1;
bool willLightOn = false;

unsigned long currentDelay = 0;
unsigned long currentMillis = 0;
unsigned long previousMillis = 0;

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(buttonPin, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(buttonPin), changeState, CHANGE);
}

void loop() {
  if(state % 3 == 0) {
    currentDelay = 100;
    willLightOn = true;
  } else if (state % 3 == 1) { 
    currentDelay = 500;
    willLightOn = true;
  } else if (state % 3 == 2) { //LED off
    currentDelay = 0;
    willLightOn = false;
    digitalWrite(ledPin, LOW);
  }

  currentMillis = millis();
    if (currentMillis - previousMillis >= currentDelay && willLightOn) {
        previousMillis = currentMillis;
        digitalWrite(ledPin, !digitalRead(ledPin));
    } 
}

void changeState() {
  state++;
}

I apologize for any lack of information that I might have forgotten as I am quite new to electrical engineering and english is not my first language. Thank you for your help in advance :smiley:

1 Like
2

I would use some type of FET to drive it.

3

It depends on the power consumed by your heating element. Power equals voltage times current and current equals voltage divided by resistance. In short P = UĀ²/R.

If either the voltage exceeds the controller voltage (5V?) or the current exceeds the permanent output current (20mA?) then you need a transistor (or relay) to turn the heater on and off. The transistor should support both the required heater voltage and current.

4

Does that refer to AWG size or 20g as in 20 grams? Be aware in your design that the point of connection of copper wire to the nichrome wire will not heat the same as the rest of the nichrome wire. The connection point will be a heat sink and draw away the heat form the nichrome wire.

5

No. The Arduino by itself can't (safely) heat-up ANYTHING! So you'll need a MOSFET that's capable if handling the required current a power supply with enough current capability.

Do you know Ohm's Law and how to calculate power (Watts)? Do you have a multimeter?

With the Arduino by itself, the "absolute maximum" current from an I/O pin is 40mA with 20mA recommended. 125 Ohms at 5V is 40mA (Ohm's Law) and that's about 200 feet of 20 AWG nichrome wire and it's only 0.2 Watts, so almost no heat with the heat spread-out over 200 feet. (That's enough power to light an LED. :stuck_out_tongue: )

That gets complicated and your best bet is probably to experiment (by applying power directly without an Arduino or anything). You're probably going to need low-voltage and (relatively) high current.

You don't exactly get a known temperature... You get a certain heat-rise, so maybe 15 degrees above ambient, etc.. And that also depends on air flow. (You did say "wire temperature" so I assume you're not trying to heat the air or anything else.)

That will require some experimentation too... The amount of power you need may also depend on time... The temperature probably won't stabilize-maximize in 2-seconds and you may need more power to heat it fast-enough.

6

Thank you for your response! How would I go about getting the required current supplied to the circuit as a whole without using a really big and bulky power supply? I am maybe using a foot of nichrome at most. Would I need to get thinner gauge nichrome?

7

Finally getting to the beginning point for your project. How much heat do you need? How fast do you need it? How much time will it need to be applied?

8

Heat: I will ideally need 35 degrees Celsius, but something lower could work if I need a compromise.
Speed: Any speed works, but it shouldn't be on all the time lest it embrittle the plastic of the goggles.
Time: I was thinking about 2 seconds, but as others have mentioned, it might be hard to immediately reach the full stabilized temperature as there is a need to heat up over time.

9

Heat is measured in calories or BTU. To get temperature, you need to know the mass of what the heat is being applied to.
Speed needs to have a real time value before you can calculate any of the other parameters of your project.

10

Alright, in that case, approximately 63 BTU, with a mass of about .5 grams.
What do you mean specifically by speed? As in the speed that it takes for the wire to heat up or something else?

11

Speed as in how many seconds to produce the heat value you need. Relates to the internal resistance
of your power supply. It will limit your current, just as does the resistance of your wire.

12

In that case, is 1 second a realistic number to require in terms of price for a power supply? If so, then 1 second should be fine.

13

A BTU is the energy needed to raise 1 pound of water 1 degree F in 1 hour. By using the energy conversion web site, 63 BTU is equal to 0.01845 kilowatt hours.
If you apply that amount of energy for one second, multiply by 3600 seconds and that is 66.42 watts of energy applied for one second.
Now, you decode what size nichrome wire and what power supply will give you that energy in one second.
If you use 12 volts, you will need resistance to allow 5.535 amps. Your wire size and length need to be what?

14

The length needs to be 1ft, thought I could loop it and make it close to 4 ft. If I did the math correctly, I would need to have 3.415 ft of my current wire at 12 volts and 5.535 amps. Is that correct?

15

That is about 70 Watts. Where will that power come from, and why do you think you need that much power to raise the temperature a few degrees, inside goggles?

Do some experiments with a power supply and a resistor, to determine how much power is actually required, before committing yourself to an arbitrary design idea.

You will probably find that a tiny fraction of that power, applied continuously, will do the job.

16

Remember, you can ALWAYS wrap the wire around a core of something that withstand the heat.

17

Perhaps if you explained WHY you want to do this?
To raise the temperaure of the goggles to 35C in a few seconds the wire will need to take a LOT of power and get VERY hot - or you will need a lot of fine wire to distribute the heat.
It would make more sense to gently warm over a longer period.

18

Are you trying to prevent the goggles from misting up?

I wouldn't want a 70W, glowing heater close to my eyes.

19

Where did the 63 BTU come from?

Was it just a stab in the dark?

20

Well, I wanted 35 degrees Celsius, and I knew that 1 degrees Celsius is about 0.55 BTU, so I converted.