PC PSU Conversion

Hey guys, I need some help with powering my RepRap. I've read every thread in the forums and every page on the wiki I could find about the subject, but I've yet to sucessfully power my printrboard with a converted ATX PSU. My attempts include splicing PS_ON to ground, +5v to a 20w 5ohm resistor to ground and +12 volt to a purple cable. The PSU either no longer turns on after modification or kills when I turn on my HBP. I'm open to suggestion for other methods of powering the RepRap or to better ways of modifying my current PSUs.

What is the 12V current rating of your PSU? IF it cuts out after the heated bed turns on, either there is a short or your PSU cannot provide enough current. You need at least 16A total.

All that should be needed is PS_ON to ground, that is green wire to any black wire. Possibly the 5V resistor, although this is often not necessary.

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Have a look here.

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[3dprinting4u.wordpress.com]

Some PSU's have a thermal cutout which kicks in whenit becomes a bit overloaded, I had this with some cheap 350W ones I had lying around so bought this 400W one here and these work as they don't have the internal cutout controller

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Experimenting in 3D in New Zealand

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and +12 volt to a purple cable

That is where you went wrong. Purple is the 5V standby and there is no way that should be connected to 12V.

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[www.hydraraptor.blogspot.com]

Alternatively you could use a hot swap server power supply, they have high current 12V rails. My prusa is powered by one of these doing the conversion here. I ended up with 4 of them as they were very cheap, message me if you want any more info!

NewPerfection Wrote:
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> What is the 12V current rating of your PSU?
+12v @ 19A. It was puled from an old HP computer. It's 300 watts.
In the case of connecting a +12v to a purple cable, I was following this guide here.

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For a 20 pin it is common to require a Double Jump green to black and purple to yellow. You can get a permutation of 4.8-5v and 7.6-8.4v combined to giving out ~ 11.4-12.8volts on the four pin plug used for the Printrboard. If the plug is not required for the board,

Unfortunately this paragraph is complete nonsense. Don't believe everything you read on the web!

Purple is a 5V standby rail that is generated by a separate small converter that runs even when the main converter is off. How can it make sense to feed 12V into it? To get 12V you use the yellow 12V wires and put a dummy load on the red 5V wires.

Edited 1 time(s). Last edit at 08/07/2012 01:51PM by nophead.

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[www.hydraraptor.blogspot.com]

yellow_fish Wrote:
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> Alternatively you could use a hot swap server
> power supply, they have high current 12V rails. My
> prusa is powered by one of these doing the
> conversion here. I ended up with 4 of them as they
> were very cheap, message me if you want any more
> info!

Those are great value for the price. Did you do anything with the fan? The fan on my mine is pretty noisy even after reducing the voltage to it.

nophead Wrote:
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> Unfortunately this paragraph is complete nonsense.
> Don't believe everything you read on the web!

Haha, yeah I guess you're right. That doesn't make much sense at all. As for putting a load on the +5v line, what do you recommend? Most places suggest a resistor, but I haven't seen a consensus on what type is best.

bobc Wrote:
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> Those are great value for the price. Did you do
> anything with the fan? The fan on my mine is
> pretty noisy even after reducing the voltage to
> it.

They really are, I have a few left over too for my next printer(s). 40A supply for under £20 is pretty unbeatable! I struggled to find a PC PSU that had high current rails then found how cheap server ones are! The fan is pretty loud, although still quieter than my old PSU which was a Chinese one off eBay. I've been eyeing up the fractal design 80mm fans as they are so cheap and claim to be silent, time will tell how quiet an 80mm fan can be whilst still being effective at cooling.

A 10R resistor works as a dummy load.

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[www.hydraraptor.blogspot.com]

yellow_fish Wrote:
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> They really are, I have a few left over too for my
> next printer(s). 40A supply for under £20 is
> pretty unbeatable! I struggled to find a PC PSU
> that had high current rails then found how cheap
> server ones are! The fan is pretty loud, although
> still quieter than my old PSU which was a Chinese
> one off eBay. I've been eyeing up the fractal
> design 80mm fans as they are so cheap and claim to
> be silent, time will tell how quiet an 80mm fan
> can be whilst still being effective at cooling.

I'll have to look into one if trying to fix my current ones fail. As for the fractal design fans, the ones in my computer are quiet. At least imo.

nophead Wrote:
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> A 10R resistor works as a dummy load.

I'll get one and see if it fixes my problem. Thanks.

sparkfun has a very handy breakout board for atx psu's i got it for my other one and i find it very handy https://www.sparkfun.com/products/9774

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[mike-mack.blogspot.com]

i followed this wiki and works like a charm on my old psu
[www.wikihow.com]

its powering my heatbed and sanga, its a little work and PLS WHATCH OUT the capacitors can be still loaded and can kill you, leave the psu out for a while before you work on it or load it so the capacitors can unload.

I added an 8ohm 20w sand resistor across the +5v line and my PSU works like a charm. Thanks all.

great news!

A 12V light bulb also makes a nice 5V load, as well as an old CD drive or hard disk (for example the one in the PC you salvaged the PSU from).

More reliable info on how to "convert" an ATX PSU is in the RepRap wiki: [reprap.org]

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Generation 7 Electronics	Teacup Firmware	RepRap DIY