Question Regarding reverse voltage on combining powersupply wires

[john2376]

I have a power supply I'm gonna "convert" into a general power supply for various experiments, but one specific thing is bothering me,
and it's about if I can combine the various 12V, 5V and 3.3V (respectively/separate per voltage), and if doing so, should I be worried about reverse voltage? (I assume if yes, then suitable diodes should do the trick).
The power supply is a Corsair cmpsu-650TX, with what I understand as, having single rails per voltage.

(Manufacturer product website)

 

[jay32267]

Well....I was wondering that myself and I found this.

"most PC power supply returns are all tied to each other. There typically isn't an isolated output "

So if this is true with your power supply.....you can't combine them.

In other words....if they all have a common ground (return)....they won't combine.

 

[john2376]

Well....I was wondering that myself and I found this.

"most PC power supply returns are all tied to each other. There typically isn't an isolated output "

So if this is true with your power supply.....you can't combine them.

In other words....if they all have a common ground (return)....they won't combine.

I read your reply yesterday and re-read today, but my ape-brain cant wrap itself around the logic of it,, For, it all returns are tied to each other, I mean, if the outputs aren't isolated.. I am just.. confused.
My resorting to posting a thread on this, it's mainly for the logic of not drawing too much current on a single wire, since 12V at say 50amp is quite a bit too much for one or just a couple of the wires to handle.

Also I was sort of under the assumption that a power supply's different wires is output from the same sources (per voltage), but mainly have a plethora of wires to accommodate the various electrical components it powers within the computer.

 

[TJ Hooker]

"Combine" them how?

 

[jay32267]

I read your reply yesterday and re-read today, but my ape-brain cant wrap itself around the logic of it,, For, it all returns are tied to each other, I mean, if the outputs aren't isolated.. I am just.. confused.
My resorting to posting a thread on this, it's mainly for the logic of not drawing too much current on a single wire, since 12V at say 50amp is quite a bit too much for one or just a couple of the wires to handle.

Also I was sort of under the assumption that a power supply's different wires is output from the same sources (per voltage), but mainly have a plethora of wires to accommodate the various electrical components it powers within the computer.

I'll try to explain it.
By "combine"...I'm thinking you mean "add"?
As in....could you add the 12V and the 5V and get 17V?
You can do this ONLY if they are isolated from each other.
Which.....I read that.....MOST PSU power supplies are NOT.

If they aren't isolated.....they share a common "ground" and they can't be separated. By sharing a common ground I mean all the negative terminals of all the voltages are connected to each other....and these are usually connected to ground.

As far as drawing to much from a single wire.....the PSU may not let you.....but if it does....you can go by the gauge of the wire. Find the wire gauge.....and look it up and it will tell you how much current that wire can carry safely. I'm thinking around 10-20 amps per wire depending on the gauge.

 

[SkyNetRising]

As in....could you add the 12V and the 5V and get 17V?

They have common ground.
So if you connect your device one wire to +12V, other wire to +5V, then you'll get 7V.

If you tried to connect +12V to ground or +5V to ground, then you'll get short (obviously).

 

[john2376]

"Combine" them how?

Basically just combining all the wires per individual voltage, say all the 12V wires to one 12V, all the 5V to one 5V and the same with 3.3V, or to fewer outputs at least.
So that is, not combining all the wires into one single output, rather just combining the respective voltage wires into less of a mess of wires.

 

[TJ Hooker]

Oh, yeah that should be fine. You could also try your hand at replacing the wires with a single wire if a gauge or your choosing. I'm not sure how exactly the wires would be attached to the voltage regulator outputs, I imagine either screws or solder.

 

[john2376]

Oh, yeah that should be fine. You could also try your hand at replacing the wires with a single wire if a gauge or your choosing. I'm not sure how exactly the wires would be attached to the voltage regulator outputs, I imagine either screws or solder.

Basically what I had in mind, then connect the combined wire per voltage to 'banana' connectors with individual colors (red for 5V, yellow for 12V and so on), and make a little hub of acrylic glass where the connectors would be screwed onto, and also have an AM-meter (ampere) per the three main voltages to be able to see how much current is output.
But back to one basic detail with my original question; take for example combining the 12V wires, is there any risk of a reverse current going back from one output cable to another output, or is it more likely that it's simply one single +12V output being fed through the many 12V cables?
(I sort of thinks so based on how a computer needs the same voltage for many different components, but wiring it so that the motherboard have to pass the current would be too inefficient to design, thus having many cables passing current from the same output makes it more modular and easier(cheaper),).

 

[TJ Hooker]

is it more likely that it's simply one single +12V output being fed through the many 12V cables?

Yes, this is the case. There should be no issue shorting together all the wires for a given voltage rail.