Been some good posts lately, lets continue the stoke.
A good friend helped me out with some eps blanks, so I decided to make my own hotwire setup. First things first, I needed a power supply. After a bit of looking online, I decided the most flexible setup for me was to use a computer power supply I had sitting around. The site below has a neat calculator that can help you estimate the approximate voltage and current for various gauge wire of different lengths.
http://www.jacobs-online.biz/nichrome/NichromeCalc.html
I decided I wanted approximately up to around 15 amps, at 3 volts and 12 volts DC.
Technically I would need variable voltage, but I designed an addon to my computer power supply that does PWM output to get varying current at the voltage output from the power supply. Specifically I used the 3.3 volt line, and the 12 volt line. I then fed them into a N-Mosfet, which is basically a switch. I then used a microcontroller to switch it on and off. Then the duty cycle determines the amount of current going through the wire. The duty cycle is controlled through a potentiometer, that is read from the microcontroller. I ran the positive lead through another chip that detects the amount of current going through the wire, and output that to the led display.
It works pretty well, here is the parts list for the main parts;
led pushbutton $1.5 16mm Illuminated Pushbutton - Red Latching On/Off Switch : ID 1442 : $1.50 : Adafruit Industries, Unique & fun DIY electronics and kits
led display $9.95 Adafruit 0.56 4-Digit 7-Segment Display w/ I2C Backpack - Green [STEMMA QT / qwiic] : ID 880 : $9.95 : Adafruit Industries, Unique & fun DIY electronics and kits
arduino microcontroller $7.95 Adafruit Trinket - Mini Microcontroller - 5V Logic : ID 1501 : $6.95 : Adafruit Industries, Unique & fun DIY electronics and kits
20 amp current sensor(ACS712) $5 http://www.allegromicro.com/en/Products/Current-Sensor-ICs/Zero-To-Fifty-Amp-Integrated-Conductor-Sensor-ICs/ACS712.aspx
10K audio taper potentiometer $2 radioshack
10K resistor, 0.1 microfarad capacitor, 1 nanofarad capacitor, banana plugs, banana plug outlet, circuit board, dpdt switch, spdt switch rated at 20amps, fuse holder 20amps, project box $20-30 radio shack
It wasn’t too hard to put together, and if you can build a surfboard, mix resin right, use a planer, this is doable. What I liked about this method is , if the smoke goes out of any part I can replace it. It also works with any pc power supply. I didn’t alter any of the internal parts of the power supply. Also Pc power supplies are pretty robust as they are designed to be run constant for several years, at more than the current needed for my hotwire setup. I will post a circuit diagram later.