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I have an adjustable power supply (TENMA - two channels 30V-3A and one 5V-3A I think) and I want to get a +-12V rail from it. By putting the supply into series it says that it has internal relays so I assume I don't need to bridge something (right??). When in series mode I can seem to understand how to get positive and negative 12V potential in respect to the ground... What am I doing wrong?

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enter image description here

You should wire the power supply like above picture. Put both 30V channels to 12V. Then connect them in series. The wire connecting the - to the + is your reference.

I think you are confusing the ground with your reference voltage. Ground is attached to the wall plug of the power supply which is not the same as your reference voltage.

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  • \$\begingroup\$ you are right, I did confuse the 'ground' with the reference but I think my confusion was amplified because I read in the manual that there is an internal relay in "series mode" and I couldnt found a pair of +,- or ground that I could get +/-12. Ill test with the bridge. thanks. is there problem if there is an internal relay that links the terminal and I bridge them also externally? \$\endgroup\$ – OHTO May 20 '14 at 13:55
  • \$\begingroup\$ @OHTO In series mode, the outer + and - clamps will be the +12 and -12 supplies. The middle + and - clamps will be your reference. If you measure the voltage, put you return lead in the reference, then measure the voltage with respect to the reference. It should display +12 between + and reference and -12V between refence and -. \$\endgroup\$ – Matthijs May 20 '14 at 14:07

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