Once again I have seen recent topics with power problems. Trying to run and ESP8266 from the 3.3 volts from an Arduino NANO (as pointed out that is a 5-10X overload on the regulator). Running dozens of LEDs with an UNO connected via USB fails when using only Vin connected to a 12V supply.
In both these cases the onboard regulator is being overloaded and with luck shuts down to prevent damage. The onboard regulators are designed to power the processor and a couple of LEDs and low power sensors. So get out a file card or piece of paper and write down the often repeated phrase.
THE ARDUINO IS NOT A POWER SUPPLY
Post it where you are doing development as a reminder.
USB also has limitations on supplying power. The original spec limited power to the 100mA to 500mA range. Newer specs go to 2A or more, depending on the implementation. If your project works on one machine and not another it may be due to different power specs. If it runs for a while then stops but then runs for a while again after being disconnected for a time, it is probably due to a slow acting current limit when overloaded.
Perhaps, this should be a Tutorial? Perhaps there is one? Or maybe an FAQ for beginners? Not that they'd read it, given the lack of "how to" awareness.
Not trying to derail your rant, but wouldn't it be nice if, on the Tutorials forum page, there was a search button which would allow the newb to search the Tutorial section for keywords like "power"?
It surely should, and likely is. The sad fact is that there's so much crap, "tutorials" made by ignorant and for a short time, lucky people.
Even a knowing guy like dronebot defends his use of PP3 cells pointing at a crappy fact that kits are delivered with cable connections for the PP3. I tried telling him that he creates a lot of work for the Arduino Forum but his ears were deaf.
Using Vin is still a problem for many. I did some calculations and here are the results. The UNO uses the NCP1117ST50T3G regulator to generate 5V from Vin.
Data sheet here.
From the data sheet pages 2 and 8 it appears the maximum power dissipation is about 600mW. The difference between Vin and 5V will be dissipated as heat so dividing the max power by the difference voltage will give the maximum current.
Vin......Difference .......Max current
12V............7V...................85ma
9V.............4V..................150ma
7.5V..........2.5V...............240ma (I use this)
7V.............2V................. 300ma (test voltage page 3 of data sheet)
6.5V.........1.5V................400ma (minimum on page3 of data sheet)
(Anyone know how to prevent deleting extra spaces??)
I use a 7.5V wall wart, which will work even with clones which might have a regulator with a higher dropout voltage.
Vin Difference Max current
12V 7V 85ma
9V 4V 150ma
7.5V 2.5V 240ma (I use this)
7V 2V 300ma (test voltage page 3 of data sheet)
6.5V 1.5V 400ma (minimum on page3 of data sheet)
I cheated, did it in IDE as a comment block, then removed the comment /**/ in the reply box.