I was wondering if my 12V power adapter would work with the Arduino Uno, and more specifically, how much current is safe to use with it. I know that 12v is okay to use, however, I am not sure how many mA is allowed through.
Would a power supply with 12V DC @300 mA work?
Yes, as long as the Uno is the only thing using it. Actually, other things could use it as well but you have not described them so I cannot say that they are safe.
The Uno will only use as much of the 300mA as it needs. It needs about 50mA, so an additional 250mA is available that will go unused.
From https://store.arduino.cc/usa/arduino-uno-rev3:
The board can operate on an external supply from 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may become unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.
Of course, this assume that your power supply actually supplies DC at 12 volts, and that you have connected it properly to the Uno.
Good Luck!
Thank you for your reply.
In the time between your reply and this reply I have found a 12v @ 2000 mA power supply. This would still work, correct? So it would only use ~50mA and 1950 mA would be available?
My second question is I am using an electromagnet in this project rated at 12V at .84A (840mA) and want to power it using the same supply. In this case, the available current would then go down to 1110 mA correct?
I just want to make sure everything works and stays stable!
Thanks for your help!
You have done the math correctly but there are more subtle reasons why you should not power your Arduino and an electromagnet from the same power supply. It would be best to power the Arduino from the smaller supply and the electromagnet from the larger supply. If the Arduino is going to control the electromagnet then connect the negative lead of both power supplies together to provide a common ground point.
So it would work, except it would be more efficient to use two sources?
vaj4088:
The Uno will only use as much of the 300mA as it needs. It needs about 50mA, so an additional 250mA is available that will go unused.
Available current from the regulator depends on how much work it needs to do. If it has to regulate down from 9V, it's about 350mA, at 12V it's about 200mA.
Using an external buck converter saves the board from the heat and improves efficiency of the overall setup as you're not using a linear regulator.
The use of two sources is not an efficiency issue.
The issue is to avoid damage to the Arduino, and to avoid disrupting its operation. It is usually a bad idea to share a power supply between the Arduino and a high-power device such as a motor or an electromagnet. High voltages can be developed, and disruptive noise can be generated. Play it safe and use separate supplies.