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I have constructed a series circuit to power the arduino uno from a 12v to 14v battery. The battery fluctuates do to solar panel. The circuit continuously supplies 8.5 to 9.2v. The supply is plugged into the barrel jack. The 5v output pin is only giving me 3.3v. When using usb from computer to usb on arduino I get 5v and also get 5v when using ac adapter to arduino barrel jack. Any help is appreciated.

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  • Some Arduino boards / processors run at 5v and others at 3.3V. Some run at both voltages but at the lower voltage the processor has to run slower. If the 5v and 3.3v are measured using the same board then you probably have a problem supply enough current from your solar / battery power source. Some power regulators need several volts difference to work as expected. If your Arduino processor is supposed to work at 5v then make sure that your solar / battery power source is supplying 5v + regulator-voltage (unless LDO then use at leas several volts here) while under load. – st2000 May 17 at 4:13
  • "also get 5v when using ac adapter to arduino barrel jack" Are you sure? Because that seems really unlikely. The only way I can think of that happening precludes the idea of you also getting 3.3V when 9V is fed in. Please verify that you have all the facts correct in the question. How much you're loading the regulator may also be important to know. Also which Arduino? – timemage May 17 at 11:01
  • Check your grounds they should all be connected in a single point configuration. – Gil May 18 at 1:21
  • Thanks for your input. The series circuit comes straight from the 12v battery. The battery fluctuates up to 14.2v during peak. The lowest voltage from circuit to barrel jack is 8.5v. If I connect the usb from charge controller to arduino there is no issue. The arduino works fine and works the load no problem. The circuit I constructed changed the 12v to 8.5 to 9.2 volts at the barrel jack. The load (relay) does not operate. The 5v pin is only producing 3v using the barrel jack. The code works fine with the usb to usb. Granted I am new to arduino. All help is appreciated. – Kelly May 19 at 2:00
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    This is the arduino uno. – Kelly May 19 at 2:10
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The voltage output of a series resistor circuit will change with the load. Post a schematic as requested earlier that way you could get a solution.

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