Hi
I was wondering about the max voltage that I can use to power an UNO R3?
The tech specs say "Power : Input voltage (nominal) 7-12V". However if you just use a not unregulated 12 volt wall wort the open circuit voltage could be 15v and then depending on the load it will drop to the rates 12v. That is why I am asking about the max voltage for the power supply to the UNO.
Stan
I would not put more than 9V into an Arduino! The excess voltage is converted to heat!
12 volt is a value that sould never be exceeded. Use regulated voltage supplies in order to stay away from unexpected trouble. To have some margin, 9 volt is less bad. The very best is using 5 volt into the 5 volt pin.
The specs for the Uno say:
Input Voltage (recommended) 7-12V
Input Voltage (limit) 6-20V
So a brief input voltage of up to 20V won't harm the Uno. The critical word here is brief. But any voltage into the barrel connector will generate heat in the voltage regulator on the Uno. This is bad because over a long period of time, probably hours or more, the excess heat in the regulator will accumulate and ultimately make the regulator fail.
Why is there a barbell connector? The Arduino is a learning tool and not intended for commercial projects. A student would be expected to plug in a 9V battery pack to test their software exercises. That 9V battery may last for a few days, but it won't power a long-term project.
As others have said, the best way to power any Arduino is by injecting a regulated 5V into the 5V pin on the board.
All that said- I have a project I did years ago that is powered by a 12V wall-wart, and a Wemos D1 Mini powered from the 3V pin of the Arduino. All in violation of good engineering practices, but still working today.
Okay. Thanks everyone for the info.
It is much appreciated.
Stan
I use one in a car so it's generally running a little more than 12V and no problems. (Some people worry about voltage spikes but I've been OK in this particular vehicle.)
The on-board regulator gets hotter with more current so it depends on how much "other stuff" you are powering through the regulator.
I'm running few LEDs and when all of the LEDs are on I might be slightly-exceeding the combined limit of 200mA for all of the I/O pins.
And "UNO". The original item is constructed using quality components, not so all of the copies and counterfeits, many of the latter mendaciously advertised as UNOs when they are not a UNO at all but a variant of the much older Duemilanove which did not have the 16U2 USB interface which marks the actual UNO.
I'll omit the rant about the wisdom deficit of actually using the "barrel" (not "barbell" 
) jack or "Vin". 
May be a memory of the days when cars had mechanical voltage regulators. See, I remember! 
That may have been true 20 or 30 years ago before computers in the cars were commonplace. The biggest spike was when the starter solenoid was connected directly to the IGN line. When the starter motor disengaged from the flywheel there was a HUGE reverse EMF spike. They are now more isolated from the IGN bus.
This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.