Hello, I am struggling with this project and was hoping for some guidance. In essence, I am trying to replicate the way an electronic hand-warmer functions, but cut-down to the basic essentials and small, I've looked into many posts by others creating warmers using PID/PWM and just haven't found something matching what I want to do and am struggling. Here is essentially what I've figured out I will need:
Controller (Nano most likely)
Thermistor for adjusting PWM
Power source (Li-Po batteries with charging board attached, 7 or 8 Volts)
Nichrome wire
MOSFET transistor
Button (to turn on/off and swap between low, medium, and high temp)
I think I can manage programming the arduino and calculating the amount of nichrome to use, but I feel like I'm missing something and I don't know which specific transistor or resistors I should use or how they should be properly ordered/connected. I would sincerely appreciate a nudge in the correct direction, I only need something simple with 2 or 3 heat settings.
Here is an example of what I'm replicating: Amazon link to hand warmer
Forget all the rest, for now, and just make the heating elements and make sure they work properly with the battery you will use. No need for anything else until you get that working correctly. Then you can design and build the control works.
Rather than using nichrome wire, I think you may be better to just use a bunch of ordinary resistors. Since they are very cheap, you could use, say 50 of them in some arrangement to dissipate the required power.
Fifty quarter watt resistors could dissipate 12.5 W, so 5 W would be a more practical maximum dissipation and you could calculate the values to do that perfectly.
Once you name your preferred battery.
I've already done this, and confirmed it works. There are pre-built heating element pads that work great but you can also just measure a proper amount of nichrome. It's really just the transistors/resistors that I'm having trouble with understanding, as I'm not an electrical engineer.
Here is a MOSFET driver circuit.. It's named a "motor driver" but it can be used for anything that needs more current and/or voltage than you can get directly from the Arduino, and it will 'pass through" PWM (if you really want to use PWM).
Do you know how to calculate current? Ohms Law... Current = Voltage/Resistance.
And be careful not to over-stress the battery... Li-Po batteries can literally burn-up, although the good ones should have an internal thermal fuse so the battery just permanently dies without starting a fire. The Amp-hour rating tells you how long the battery charge will run and the actual current limit may be more or less.
Heating & cooling devices rarely use PWM, and I doubt that Amazon thing has a microcontroller.
Heat can't change instantly so usually a heater turns-on until the target temperature is reached and then it turns-off until it cools down again. And usually there is some "swing" of hysteresis so it turns-on a little below the target and of when it's a little above target. That's to keep it from switching on & off hundreds or thousands of times ever second. In a home heater that's usually about 1 degree but you can make it tighter.
This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.