Although I’m an experienced programmer I am fairly new to Arduino.
I am building a project where I am using an Arduino Mega and a stepper motor driver together with encoders, LCD, temp and IR sensors.
In order to cool the driver heatsink, I have 2 x 5V (0.14a) Brushless DC Fans. I understand I cannot just connect this on the I/O pin as its above the mA limit.
The Mega will be powered with a 5V (2A) power supply via barrel jack.
I’ve read online using a MOFSET however all the examples I could find, use an external power supply.
My question is: If I am using an external 5V (2A) power supply plugged in the barrel jack, can I use the 5V pin & GND pin for the MOFSET or would I need an additional power supply?
That won't work. The barrel socket requires at least 6.5~7V. You could power the Mega through the 5V pin, though. Take separate wires from the PSU to power the fans, you don't want the fan current flowing through the Mega PCB.
What's the problem? You are also using an external power supply. The Mega isn't a power source, after all!
Don't forget flyback diodes across the fan power wires. Without those, the Mega could be damaged, even when using MOSFETs.
On Amazon you can get this, MOS FET PWM 3-20V to 3.7-27VDC 10A 4-Channel Driver Module PLC Amplifier Circuit Board. It will do what you are trying, plus you will additional channels for future use,
I run a 12 volt camper fan with mine, I use PWM to control the speed.
Important rule: A Power Supply the Arduino is NOT! The fact that what you found using a MOSFET with an external supply should indicate that there might be a valid reason for that configuration! If you go that route be sure to have lots of spar Arduino's.
Currently I have the 5V (2A) power supply for the Mega (which I am replacing with a 9V (2A)).
I also have a 12V (6A) power supply which is controlled by a relay (5VDC operated digitally) going into the CNC Shield I use for the 4 steppers.
What I will do is run in parallel on the 12V line a DC-DC step down to reduce on one line 12V down to 5V. This way, everytime the CNC Shield is receiving power, the fans will be running which was what I was intending of doing anyway.
By stepping down the 12V on the separate input, which is not connected to the Mega, I will avoid any interactions between the Mega and the 5V of the fans.
Slowly learning everyday but thanks so much everyone for your help!