I'm building a hot wire setup to do various hobby projects. I've got most of it figured out already, thanks to the wealth of information there is out there. I have a 12V switching power supply with a max current of 10A to heat the wire. One thing I'm trying to work out is fine tuning the wire temperature. I tried simply putting a pot in the circuit after the power supply, before the wire, to essentially modify the power supply's output voltage. Predictably, though, the pot got hot. Really hot. Obviously, I'm not happy with that as a solution, since burning my fingers while trying to adjust temperature doesn't sound appealing.
My next thought is to use PWM to control the temp, and, again, there is some information out there to support this. However, I'd prefer to use a very simple controller. I've already built a small motor controller that uses PWM, the schematic provided by this site:
http://makezine.com/projects/the-dial-a-speed/. I'd be concerned that this wouldn't handle the kind of current I'm pushing through the wire (1.5-2.25A by rough calculations), however. Plus, if I want to use a higher voltage with the wire, it would almost definitely fry the controller. Could I control a relay with PWM that in turn shuts power on and off to the wire? Or does someone have a much better idea for me to look into? To preface, I'm a mechanical engineer, so I have a basic knowledge of circuits, but the simpler the better. Thanks for any assistance!
Best Answer
The schematic you posted (dial a speed) is suitable for your needs. The stated FET(IRF510) tolerates 100V 4A, so it could handle your hot wire with proper driving/cooling. If needed you can find many alternative FETs with lower voltage rating and higher current rating really cheap.
A relay would theoretically work for driving a low frequency PWM, maybe less than 1Hz (I believe you dont need high frequency). However in practice it is never done and I would avoid that route, especially if you have already built FET PWM controllers.