DC Polarity Question

Discussion in 'The Projects Forum' started by arfinator, Nov 22, 2010.

  1. arfinator

    Thread Starter New Member

    Nov 21, 2010
    Hey, guys!

    This is my first post here, thought I have looked around quite a bit. Everything on here has helped immensely!

    I have a AC/DC transformer that outputs both 12VDC and -12VDC relative to the ground. Can I use the -12VDC output without changing anything, or do I need to include something to change that to +12V?

    If so, how might I do that?

    Thank you so much, and I look forward to your response.


    Please note that as of right now, this is an entirely theoretical project. I plan to have it looked over to ensure my safety and the safety of other users before it is put into practice. :)
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    If it is a dual output power supply, you should have a black jack (-12V), green jack (ground), and Red jack (+12V), or colors similar to that. If you measure between the red and black jacks, a DMM will show 24V.

    Usually, -12V is only 1.5A, while +12V can be 1.5 to 40Amps (depending on if you are using an ATX computer supply or basic hobby type supply) The max current from -12V is the limitation on using the 24V supply.

    If not interested in "bridging" for 24V, then ensure both -12V and +12V are regulated, you can do this by measuring voltage without a load and writing it down, then hooking up a 12V light bulb, and the voltage should be within 0.1V of unloaded for a regulated supply.

    If this doesn't match what you are looking at, please post a photo.