MG2R
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Mon Dec 19, 2011 10:45 pm

In another thread, someone said it would be nice to be able to use an old PSU to power the r-pi. I tought it would be nice to share the information to the rest of the community.

It's possible to convert PC PSU's into stand alone units which may supply 3.3, 5, 12 and 7 volts. The color code for these PSU's is as follows: RED: +5V, YELLOW: +12V, BLACK: GND, ORANGE: +3.3V PURPLE: +5Vsb . That means that you can get 7V between the red and the yellow wires. On top of that, it can provide a small amount of power to a 5V standby connection.

But how do you power on a PSU without a computer attached to it? This can be done by connecting the GREEN wire with a BLACK wire on the 24 pin ATX connector.

For a tidy PSU you could open the unit up an trim all the cables. Drill 6 holes in the case: 5 for banana connectors or something similar (GND, 3.3V, 5V, 12V, 5Vsb) and one for an off/on switch. Connect the switch between the green and black wire. When the PSU is off, the 5Vsb should still be available!

Some PSU's require a minimum load to function properly. Therefor, it's safer to solder a 10ohms, 10Watt sandbar resistor between one of the +5V wires and GND. For better cooling of the resistor, you could zip-tie it to the enclosure, like so.

The 5Vsb should be able to power an r-pi. The psu itself could be used to power 250 r-pi's :D

--EDIT--
I *KNOW* that this is VERY inefficient to just power 1 R-pi. This is actually intended for use on test benches or on a whole bunch of r-pi's and their accessories (hard drives, etc, etc)

If you are not familiar with electric/electronic components and do not have experience with high-voltage circuitry, then DO NOT OPEN UP the PSU. If you do open it up, then NEVER EVER touch the capacitors inside (you should be fine if you leave the PCB in the enclosure.

You can do this hack without opening up the PSU by using the external cables. I usually open the PSU up, so I can solder all of my connections out of side and so I can screw my connectors through the enclosure.

obarthelemy
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Mon Dec 19, 2011 10:51 pm

This would be terribly wasteful though. You'd probably save the price of an appropriate PSU ($5 ?) over a few months.

MG2R
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Mon Dec 19, 2011 11:08 pm

Quote from obarthelemy on December 19, 2011, 22:51
This would be terribly wasteful though. You'd probably save the price of an appropriate PSU ($5 ?) over a few months.
Completely true about that! But this is more intended as a simple and cheap test bench power supply (for hackers). If you just want to power your r-pi, you're better of with something else ;)

--EDIT--
If you use it in standby to power the r-pi it might be just as efficiënt as a power brick.

mobeyduck
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Tue Dec 20, 2011 12:30 am

This solution can easily be used if you want to build the R-Pi in side of you current computer.

I've seen one guy posting he wanted to use the R-Pi while his pc was rendering who wanted exactly that

MG2R
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Tue Dec 20, 2011 12:38 am

Well, he just has to hook it up to the 5V and GND on a free molex-connector :)

wrhii
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Tue Dec 20, 2011 2:47 am

Guys, this is not the best way to power a Pi. A simple cell phone charger will do the trick with less load, and less risk of injury.

It also has lower risk of melting that nice new Pi-toy into a pile of Pi-tin...

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Jessie
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Tue Dec 20, 2011 5:16 am

I was thinking about using this option if I were powering like 20, 30, or 100 R-Pis but for one an ATX PSU wastes a ton of energy even at idle.

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Vindicator
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Tue Dec 20, 2011 6:57 am

Oh come on the PSU only weighs as much as 30 or 40 Rpi's also, but in the spirit of experimenting it at least sounds fun HEH.
Ive thought of installing a Raspi into my PC with a small touch screen for the fun of it and the info tells others were they might get it, I was just going to use a USB data cable to get my power from the PC but this is just another approach.
My way is just a easier/lazy way to do the same thing.
You could slave in a full size SATA drive with this approach.
If you are more worried about ,spelling, punctuation or grammar you have probably already missed the point so please just move on.

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reiuyi
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Tue Dec 20, 2011 2:55 pm

If I remember correctly, both 12v and 5v need some load for an ATX power supply to function correctly. Also, it's very much possible that (especially the cheap PSU's) will have like 33% efficiency below 100W, as the efficiency of an ATX PSU is not flat.

I'd still find it cool if someone placed a Raspi in a large midi-tower with a big USB-hub and several usb->IDE and usb->sata to connect a diskdrive, harddrive, floppy, multiple usb ports at the front and back, proper usb soundcard with mic in etc etc. It'd be a full computer, yet running at like 5W!

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abishur
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Tue Dec 20, 2011 3:28 pm

It would be a very effective solution for powering multiple r-pis and peripherals, just remember to be careful if you go opening your PSU (as in if you don't know much about electricity, don't do it!) ;)

They're safe to work on if you know what you're doing, but if you don't... well the results can be shockingly deadly
Dear forum: Play nice ;-)

arm2
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Tue Dec 20, 2011 9:34 pm

One PSU manufacturer has also told me that their latest 350W 80+% efficiency PSU needs a minimum load on the 3v3, 5V & 12V rails.
Another manufacturer said their PSU needed no minimum load! When I get an RPi I will give it a try!

MG2R
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Tue Dec 20, 2011 10:05 pm

Quote from arm2 on December 20, 2011, 21:34
One PSU manufacturer has also told me that their latest 350W 80+% efficiency PSU needs a minimum load on the 3v3, 5V & 12V rails.
Another manufacturer said their PSU needed no minimum load! When I get an RPi I will give it a try!
In my experience (with old PSUs), if you don't put a load on the machine, voltages are about 30 mV too low. With the load on the +5V rail, everything works splendid. Of course, this can vary between different PSUs.

You should however be capable of running your R-pi from the 5Vsb rail, than you don't even have to power up the PSU.

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JeToMad
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Tue Dec 20, 2011 10:10 pm

Well, I can tell you that the ones I used (I used several as lab-PSUs) always needed a load at 5V, but nothing else. By the way, think that 10R on 5V rail makes it dissipate 5V*0.5A=2.5W So you are losing as heat more power than the Pi needs...

But (There is always a "but") if you have no load at the 12V rail, it won't go 12V, it will stay at 11.6~11.8. Not a big deal unless you need the 12V to be perfect ;)

If you want to give it a try anyway, the best option is to stick the resistor to the heat sinks inside the PSU. But as several people have stated, this is dangerous. Even without the PSU conected to the mains, the capacitors can give you a punch if they are charged... With the prices of usb chargers, messing with a PSU without a qualified person around seems a bad idea to me...
Greetings from Spain!

bradburts
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Tue Dec 20, 2011 10:36 pm

Its an idea but the USB plugs are very cheap.
A cheap ATX PSU will use 4W switched off doing nothing which is a lot more than a USB plug powering a PI.

So I would pass unless you are attempting to put a PI inside a PC, for example some cool CD bay display or LED light chaser or whatever.

MG2R
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Tue Dec 20, 2011 10:44 pm

Quote from bradburts on December 20, 2011, 22:36
Its an idea but the USB plugs are very cheap.
A cheap ATX PSU will use 4W switched off doing nothing which is a lot more than a USB plug powering a PI.

So I would pass unless you are attempting to put a PI inside a PC, for example some cool CD bay display or LED light chaser or whatever.
That's why this isn't suitable just to power a Pi, as noted in my --EDIT-- ;)

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JeToMad
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Wed Dec 21, 2011 8:28 am

I was thinking... obviously you have some skills ("I usually open the PSU up, so I can solder all of my connections out of side and so I can screw my connectors through the enclosure.") so... Why not to desing a simple power supply? It is not very difficult, and you will find tons of reference desings. And you will find help in this same forum, for sure.

You will have a specific PSU, and it will be truly yours :)

If you are interested in such a solution, and need help, feel free to ask...

[It will be probably more expensive. But... It will be a better option, for sure]
Greetings from Spain!

arm2
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Wed Dec 21, 2011 10:11 pm

I found the details for the 120W PSU in a HEC MiniITX case:
> See below, the Minimum load requirement for the 120watts PSU for the 8K01
> Output Voltage MIN load MAX Units
> +5V 0.5 10.0 Ampere
> +12V1 1.0 9.5 Ampere
> -12V 0.0 0.3 Ampere
> +3.3V 0.5 10.0 Ampere
> +5Vs 0.0 2.0 Ampere

We have also noticed that some/all? hard drives seem to have a half? second pause before they start spinning up and begin to load the 12v line?
We had to return some PSUs that just wouldn't start reliable on a low power motherboard (Adding extra hard drives disn't fix the problem!)

MG2R
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Wed Dec 21, 2011 10:37 pm

Quote from JeToMad on December 21, 2011, 08:28
I was thinking... obviously you have some skills..
Nothing out of the ordinary

Quote from JeToMad on December 21, 2011, 08:28
Why not to desing a simple power supply?
[It will be probably more expensive. But... It will be a better option, for sure]
You gave the answer to your own question ;) PC PSUs grow on trees in Belgium :D
Also, I just gave this info as a tip. I have an adjustable power supply (actually two, but one is retired) which are home-made.

pvgb
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Wed Dec 21, 2011 10:44 pm

I expect that I am not alone in having hopes of running several boards as a small cluster.

It seems reasonable to try and enclose them somehow ( Old PC case ? ) and power them from inside the enclosure ( Hey - an old PC case with a PSU in it ! )
As it happens I have a couple of spare PSUs from retired/upgraded systems.

As soon as we get past about four boards, suddenly we start talking about loads of wall wart power supplies, with extension cables power distribution strips and enough cable spaghetti to put you off the idea - probably need a switch as well ... ok you get the picture.

Mutilating some cables and soldering them up is within my level of ability. I leave opening up PSU cases to those both braver and better trained in the specific issues within PSUs.

MG2R
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Wed Dec 21, 2011 11:16 pm

Quote from pvgb on December 21, 2011, 22:44
Mutilating some cables and soldering them up is within my level of ability. I leave opening up PSU cases to those both braver and better trained in the specific issues within PSUs.

You do not HAVE to open up the PSU... You could just as wel use the red and black wires comming out of your PSU to power the r-pis.

jkcpalmer
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Wed Dec 21, 2011 11:54 pm

Another option, Completely skipping the PSU is mounting a surge strip inside the Computer case for all your usb chargers then you can spend your time on making brackets to mount several r-pi's.

sylvan
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Thu Dec 22, 2011 3:45 am

Quote from jkcpalmer on December 21, 2011, 23:54
Another option, Completely skipping the PSU is mounting a surge strip inside the Computer case for all your usb chargers then you can spend your time on making brackets to mount several r-pi's.

I like it! That's really thinking outside the box!

Er, no, wait. Inside the box. :?

pvgb
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Thu Dec 22, 2011 9:59 pm

Quote from jkcpalmer on December 21, 2011, 23:54
... brackets to mount several r-pi's.

Easy.

capa polycaprolactone (http://en.wikipedia.org/wiki/P.....prolactone)

(http://www.mindsetsonline.co.u.....a5p8ci4j11 - other suppliers are available )

Unless all those small hot wall wart PSUs get above 60 Celsius and melt the CAPA.

(Did I mention I don't like Wall Warts ?)

Einstein
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Sun Dec 25, 2011 9:28 pm

In addition to the minimum load on the +5VDC rail, you also need to consider the amount of power regulation that pre-exists on a PC motherboard to account for the wide variety of noise that presents from the PC switch mode power supplies.

Sparkfun produce a kit to adapt an ATX PSU into a bench supply, it doesn't get rave reviews.

If you need to power multiple R-PI's from a single power source you could consider using a 13.8VDC bench power supply, designed to run car accessories on the bench and then use a number of voltage regulators (7805 et-al) to power the R-PI's.

Another option for larger numbers of processors from a single power supply, would be to use a tomtom power supply, some of which provide 2A on a mini USB plug.

Mind you, soldering the mini USB plugs for the power supplies can be a good test for your eye sight.

johnnysometimes
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Re: Convert an old ATX PSU to a power supply (for your r-pi)

Tue Dec 27, 2011 1:13 am

This is exactly what RasPi is all about. Old PC powersupply. Ground the green wire = free power for all sorts of stuff. Old CRT TV = composite video display + sound. Old PS / 2 keyboard with a USB adaptor. All you wealthy types saying "just go out and buy a .... "

obviously don't live in the third world - or the poorer parts of the UK fo that matter!

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