Bench supply

[scoobysnacky]

Hello!

I am currently waiting on parts for a project and decided to take on constructing a bench power supply out of an ATX 250w computer psu. It outputs +3.3V, +5V(multiple) +12V(multiple), -5V, and -12V.

My question is: is it possible to take one of the +12v outputs and make it a -9V supply for guitar pedal supply?

 

[scoobysnacky]

To clarify, I understand using a voltage divider would lower the voltage to 9v but is it possible to reverse the polarity? It’s not as simple as just swapping the ground and positive is it?

 

[SyncTronX]

Why wouldn't you take the -12 volt supply and lower (raise) it 3V to -9V? It is already - DC. What guitar pedal uses -9VDC?

 

[PRR]

The vast majority of g-pedals use Positive 9V (to common).

And yes if you truly want Negative 9V, that's what the existing -12V line is for. (It is not high current, but Ge pedals rarely need much, especially if from a battery tradition.)

 

[scoobysnacky]

Ahhh shoot. Maybe I’m confusing Centre negative for -9V. I’m showing my lack of electronics theory training. Sorry guys.

So just to clarify again....I should take one of the pos 12V outputs, drop it to 9V, and wire it so the “ground” of the psu is the centre pin and the pos12V is the outer ring. Is that correct?

 

[scoobysnacky]

I mean pos9V for the outer ring......honestly. Too early in the am.

 

[zgtc]

I don't know about the 9 vs 12 or negative, but I'd say whatever you do, just don't open the ATX as many tutorials advocate for, it is dangerous. Make it an external box and reuse the 20/24 pin connector, as in YouTube

 

[scoobysnacky]

Yes. Thank you. That’s what I’m doing. There’s no need to open it anyway. Although the pinout on mine is seems to be slightly different than most pinouts online. Online it says the green wire is the “pwr_on” switch so to speak and the grey is the “pwr_ok”. On mine it’s reversed. When I ground out the grey wire it turns the unit on. Here’s the link in case anyone is interested.

https://www.electronics-tutorials.ws/blog/convert-atx-psu-to-bench-supply.html

 

[russc]

Fit an LCD volt/amp display and an adjustable switchmode regulator and you have a very useful bench power supply. A regulator with constant current adjustment limits the maximum current draw.
Be aware when connecting your power supply to your projects - the 0v (black) is internally connected to Earth (safety ground). At least it is on any I have tested.
Usefully, the ATX power supplies are often short circuit protected.
The bad news is that they can output so much current that they could still start a fire.
Use an inline fuse or a panel mount circuit breaker (or a current limiting regulator as mentioned above).

 

[PRR]

Go by the pin numbers, NOT the wire colors.