Arduino Uno not functioning with external (Vin) power

Hi guys,

I'm doing a relatively simple project using an Arduino Uno. A 13.8V benchtop power supply is powering my stepper motor/driver, and my arduino has been being powered over USB as I program it and test. My arduino uno is mounted right next to my usb driver, which is mounted next to a solderless breadboard. My 13.8V supply and the arduino are grounded together (the grounds are connected at the stepper motor driver GND terminal).

With my code working I spend approximately .8 seconds jumping Vin to a 13.8 rail on a breadboard right next to it and unplug the USB. And now, my code won't work. The lights are on (the green power led) but nobody is home. If I unplug Vin, and plug it back into USB, I'm back in business and it functions.

I'm stumped. 13.8V is slightly over the recommended 6-12V but it's 20V tolerant, and any fully charged 12V battery is going to be 13.8V or more. I've triple checked the gnd connection. Does anyone have any idea why my code won't run?

Lots of people have had issues over 12 Volts.

Better to stay under 12 Volts rather than over as the regulator has much more work to do getting rid of excess by way of heat !

Also if its a clone then who knows what the regulator really is capable of ... gotta keep those costs down.

Is it an adjustable benchtop PSU or a 13.8 automotive PSU ?

Non adjustable 13.8. I bought it because I needed more amperage for the motors and thought the 13.8V was well within spec. Suppose I was mistaken, sigh. I just know I’m run many an arduino off a 12V SLA battery, and those are always 13+ when fully charged. I guess I’m just unlucky with this one.

Have one here and just run a feed from it to a cheap Chinese adjustable voltage regulator to give me the best of both worlds.