Power Supply adapter question

Discussion in 'General Electronics Chat' started by careless_monkey, Jun 14, 2011.

  1. careless_monkey

    Thread Starter New Member

    Jan 11, 2011
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    How could you assume that? The wires can be in any order, the only thing that is known is the connection at the plug. If you don´t have it, why not just measure the voltage? Or connect a LED with appropriate resistor and try which is which if you don´t have a meter.
  3. SgtWookie


    Jul 17, 2007
    As Kubeek says, the diagram on the label indicates that the center terminal of the plug is positive, and the barrel is negative.

    You can make a simple polarity checker out of a red LED, a green LED and a 470 Ohm resistor, like this:


    You could also use a bi-color LED if it only has two leads; the 3-lead bi-color LEDs won't work. With the bi-color LED, if the input is AC, the LED will appear orange.