Hi all! I am in the process of building a CNC controller and am planning on using an arduino board to switch on the high voltage side of things. I'll be using an optoisoltaed 5V relay to switch the mains input of a 36V 8A DC power supply that I have, a 2nd relay to switch on the power to the router on the machine, as well as a couple of LEDs, a couple of switches and 2 PC fans. In the interest of saving money I plan on using the 5V 1A auxiliary on my power supply to power the fans using a crude 5v- 12v DC voltage converter. I was going to control the fans very simply with transistors and PWM from the arduino board (albeit not the best way). I want to make sure the high and low sides are properly isolated so I plan on adding in an optocoupler between the arduino and the bases of the motor transistors. Basically the way it will work is the arduino board will switch on the 1st relay when the on button is pressed as well as a 'high voltage on' LED, that will switch the power supply on and then the PWM signal will kick in and start the fans. I'm new to arduino projects so i'm a little worried that I might overload the board, how much current can it provide? Can anyone comment as to the feasibility of this project? Cheers!
The Arduino I/O pins can supply an absolute maximum of 40mA each and are safe to use up to 20mA each. There is also a current rating for the Arduino as a whole, but from the number of outputs you mention I don't think you would exceed that. You will need to ensure that the Arduino receives a good stable supply that does not have any spikes from the various inductive loads you have in your system. There is a section of the Arduino forum that is dedicated to switching high power devices where you can probably get more detailed advice about how to design your solution.