Powering an arduino mega from a computer psu


I have found an old computer psu (probably from 1995-2000) and I was very happy because it solves (i think?) most of my powering problems :smiley:

It has the following specs:

output: 200W
red: +5V 20A
yellow: +12V 8A
white: -5V 0.3A
blue: -12V 0.3A
black: GND
orange: P.G

So i mesured the output with a voltmeter, i got +5.3V and 11.3V instead of +5 and +12.

My question is, can i use directly the +5.3V and bypass the regulator? or is it better to use the +11.3V?

and what is P.G?

Sorry for my bad english, have a nice day/night

If you've got nothing else running off the 5V rail provided by the Arduino's regulator, then 11.3V would be good.

However you probably have a few 5V analog sensors and they really should be powered from the same rail as the Arduino, so that the voltages are comparable. (Don't try to measure a sensor powered from an unrelated power supply unless all you are doing is measuring that power supply.) I don't expect that 5.3V will make any difference to the Arduino if you bypass the regulator.

You need to use a fuse.

With the PSU 5V rail capable of 20A, make a wiring error and your project could be vapourised.

Computer PSUs are really unstable at low loads (like an Arduino) and produce a lot of noise (especially older ones). Some people use a 10Ω high power resistor across the 5V line for stability, but this is obviously very inefficient.

You need to use a fuse.

With the PSU 5V rail capable of 20A, make a wiring error and your project could be vapourised.

20A @5V will easily light your house on fire if you're not careful.


and what is P.G?

"Power Good", power supply has stabilised.


Thank you for your replies.

I have an arduino mega, a 3.2" tft lcd, an ethernet shield, a 4*4 keypad, some IR sensors (tcrt5000, using 2 for now), a DHT22 and a GY-63 MS5611 module. I think that those would be powered from the arduino.

I have also 3 servo motors (sg-5010), 5 small dc motors (don't have them all for now), a 5V 8-Channel Relay interface board, some LED (about 3 or 4). I think i must power them from the psu.

If i remembre correctly i read that all the components should have rhe same ground, is that correct? if not, should i use a fuse for each circuit? (there are many black wires , are they concidered different grounds or just the same?)

Thank you again for your replies.

Do a search of ATX PSU conversion and you’ll get a ton of tutorials on how to convert an unused internal PC PSU into a mnoce lab bench one. I am almost finished doing mine…