PSU / Combine 12v and -12v rails for 24v?

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Discussion Overview

The discussion revolves around the feasibility of combining the +12V and -12V rails of a power supply unit (PSU) to achieve a 24V output. Participants explore the implications for current capacity and potential methods to increase voltage beyond 12V, considering both theoretical and practical aspects.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant inquires about the possibility of combining the -12V and +12V outputs to achieve 24V while retaining the high current capacity of the 12V side.
  • Another participant asserts that the overall current rating for the 24V operation will be limited by the -12V side's current rating, which is typically much lower (around 0.8A).
  • A later reply emphasizes the necessity of a floating load for the combined output to function correctly.
  • One participant expresses a desire to increase the voltage above 12V, asking if there are methods to achieve a voltage in the range of 14-16V.
  • Another participant suggests that if the outputs are independent, it may be possible to connect the power supplies in series, similar to connecting two batteries, but raises concerns about potential grounding issues that could prevent this setup.
  • There is mention of adjustable two-channel power supplies as an alternative, noting their limitations in current output per channel.

Areas of Agreement / Disagreement

Participants generally agree that the current capacity for the combined 24V output will be limited by the -12V rail's rating. However, there is no consensus on the best method to achieve higher voltage outputs or the feasibility of connecting the power supplies in series due to potential grounding issues.

Contextual Notes

Participants note the importance of ensuring that the outputs are floating and independent, and there are concerns regarding grounding connections that may affect the proposed configurations.

singlespeed
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I would like to increase my voltage on these PSU's to 24v. If I combine the -12v and +12v for 24v do I still get the high current of the 12v side?

+12v 70A

-12v .8A

24v... but what is the current potential?

610200994548PM_0003-vi.jpg
 
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do I still get the high current of the 12v side?
No you don't.

You must still respect the -12V side's current rating which is typically only half an Amp or similar, so that will set your overall current rating for 24V operation. Note that you also require a floating (non ground referenced) load for it to work, this part is very important!
 
uart said:
No you don't.

You must still respect the -12V side's current rating which is typically only half an Amp or similar, so that will set your overall current rating for 24V operation. Note that you also require a floating (non ground referenced) load for it to work, this part is very important!

Thanks for the reply, I figured it would inherit the lower amp side. Is there any way I can boost the current voltage to above 12? I'd like to see it slightly higher in the 14-16v range.
 
ASSUMING the outputs are floating and completely independent, you may be able to put the power supplies in series (as you would with two 12V batteries). You should be able to use a mutlimeter (with the supplies turned on) to see what the voltage is between one supply's 12V supply, and the ground (or 12V output) of the other. If it's anything but open circuit, then a connection exists between the two of them.

Unfortunately, I suspect all of these will have the ground output tied to case and the ground prong on the plug, and hence be connected through the ground line, and you won't be able to do what I suggest above. A decent (current-limiting, short circuit protecting, etc.) adjustable two-channel power supply (up to 30V) will only run you around $150-$300 new, and possibly less somewhere like eBay. However, most of these will only supply 3 or 5A max, per channel (though you can connect them in series to get up to 60V, or put them in parallel to get 6 or 10A).

EDIT: Finished dangling thought
 

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