I have a salvaged power supply brick that supplies 5amps of 12 volt power and the barrel plug happens to fit the arduino uno i have. Can I run the arduino on this 24/7?Yes, that would work nicely.I also need to power some solenoids with the 12 volts. Can I pull power out of the Vin pin? I have 8 solenoids that each take 350 mA, which I assume means that at times I might be drawing as much as 2.8 amps (.35 amps * 8 solenoids). Can I draw that much through the Vin pin without anything bad happening?Unfortunately no. There is a series polarity protection diode rated at 1 amp current wired between the DC barrel connector and the Vin pin, so that sets the max current draw limit from the Vin pin. You can however splice into the 12vdc cable before the barrel connector to utilize the full current rating of the supply. Be sure to use wire gage size suitable for the maximum current you will be drawing from the supply.Lefty
Are you certain it's not just between USB power and Vin?
Measured the current it's 2A for an hour nothing got hot besides the motor.
Where would I find it on a Uno PCB?