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Series Connect 2 Plug Packs for Split Rail Supply

epsolutions

Sep 7, 2019
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I would like to place two 12VDC plug packs in series to create a split rail supply. I have done this successfully before but forgot where to place the blocking diodes so the SMPS' don't talk to each other. Can someone please refresh my memory?

There may be all sorts of reasons this is not an ideal solution. It is just for those times when I need to cobble something together.

Once solved, I will redraw and post the completed diagram here.
series_connect_wall_supplies.png
 

Harald Kapp

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As long as the two supplies are isolated from each other: no diodes required.
If the two supplies share a common potential, diodes won't help you. That is not going to work.

You wouldn't possibly mix this up with the requirement for diodes in a parallel connection, would you?
 

epsolutions

Sep 7, 2019
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As shown in my original diagram, the negative of one supply is connected to the positive of the other in series. This center point becomes a common ground. The supplies I have here happen to be two pin so there is no reference from -DC to AC ground.

I just found this article which offers an explanation, and have amended my diagram accordingly. It is basically reverse voltage protection. Will this work for both two pin and AC grounded supplies? Any further comments or suggestions are most welcome.

https://www.cui.com/blog/power-supplies-in-series-or-parallel-for-increased-power

series_connect_wall_supplies.png
 

Harald Kapp

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the negative of one supply is connected to the positive of the other in series.
I fully understand this.
The supplies I have here happen to be two pin so there is no reference from -DC to AC ground.
Your diagram doesn't show this. When the power supplies are both fully isolated (insulation between AC side and DC side), you can connect them as shown.


The diodes you added won't do any harm but are probably useless. Unless you expect the negative leg (.12 V) to become positive or the positive leg (+12 V) to become negative. But why should this happen?
 

epsolutions

Sep 7, 2019
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It is possible that one supply will "turn on" on before the other. Nonetheless, I believe there is an arrangement of diodes that applies. I have used it before but did not keep the diagram. Maybe also a diode between the two supplies on the common ground link. I would like to figure this out and then keep a permanent record for future use.
 
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