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ATX Power Supply Help

Posted by Chijai 
ATX Power Supply Help
August 16, 2014 12:49PM
I have a standard ATX power supply that i got from an old computer.
This is it: [casedge.industrialpartner.com]

Is it enough to power all the components in a Prusa i3?(5 stepper motors, heated bed, electronics, and the cooling fan)
More importantly, i have been told that i will need to modify it or strip and combine a couple of wires, does anyone know if or how i should do this?

Re: ATX Power Supply Help
August 16, 2014 01:59PM
I would recommend 400-500 watts for everything as anything less has sob stories of dead power supplies. take the max power and half that for the 12volt rails.

reprap wiki recommends at least 240watts for heated bed machines, but not all supplies are equal, and this is absolutely pushing it!

however you may run into issues with the 300 watt delivering enough power for the heated bed. it may work for a short amount of time but that is about it, also you may have an additional nozzle hot end in the future, this would require more power. figure at least 6 amps per nozzle heater (dual resistor loads, or heat cartridges) , 5 amps peek for electronics and motors (more powerful nema 17 motors) , and 20 amps for the heated bed (15-20 amps, quality and performance varies)

. the heated bed 2 or wires of yellow should be put together as well as black because single wires can not push the current needed for heated beds, many have 3 or 4 yellow and black wires connecting to the same terminal 3 or 4 black(gnd) and then 3 or 4 yellow to the other terminal (12+). although this is optional, many heated beds still reach desired temps, it is just a good practice, and reduces the chance of a wire melting.

so in basic principle 300 watts should be enough but it often is not because much of that power goes to the 5volt rails.we want at least 240 watts of 12 volts power that would be a supply that at minimum would have a 12v current of 20amps, but recommend at least 30amps. (current requirements on heated bed are varies. you don't want to be on the harry edge, as it will cause failures at odd times)

yes people do combine wires together and it increases amount of current flow. it is only needed for heated bed power.

any questions or additions? I'm sure many people have various inputs on this subject

Edited 2 time(s). Last edit at 08/16/2014 02:05PM by jamesdanielv.
Re: ATX Power Supply Help
August 16, 2014 02:04PM
That is a 300w power supply a cheap one so it's probally only good for 250w constant. Watage wise that should be more than enough to push everything.

here is a video showing you what you need to do [youtu.be]
Re: ATX Power Supply Help
August 16, 2014 03:12PM
So basically it'll work but not everything will be fully powered? Im not planning on having a dual extruder setup anytime soon, and the fan can be powered separately for the time being. Is it better to have more amps than less at 12V?
Re: ATX Power Supply Help
August 16, 2014 06:59PM
yes you want more amps for 12v. for simplicity 5v circuits are not used by reprap in current configurations (ramps), the voltage is stepped down to 5v for the board logic by a voltage regulator on the board. If you do not have the amps (current) voltage will drop off, and electronics drivers will suffer in performance, and heated bed will not heat properly. also if power supply is saturated, and the voltage drops it may cause internal damage to parts that can not cool fast enough. the best power supplies are upwards of over 80% efficient. many are less.

with power supplies online in the range of 30-40 dollars, I would think it a wise choice to get more power. however if your specs are at 12v provide more than 20 amps you may be ok.

one thing you could consider is to make a prusa without a heated bed and add it later on. this would save you money upfront.

Edited 1 time(s). Last edit at 08/16/2014 07:00PM by jamesdanielv.
Re: ATX Power Supply Help
August 16, 2014 07:06PM
Ok this might be what i end up doing, because i really only need to print in pla, so i guess ill upgrade to a heated bed along with a new psu later on. So without the heated bed do i still need to strip and combine part of the cables?

this was the tutorial that i was gonna go off of:[www.youtube.com]
Re: ATX Power Supply Help
August 16, 2014 09:23PM
no, the only parts that require the current provided of combining the wires was for power to the heated bed. but it wont hurt it if you do.
Re: ATX Power Supply Help
August 16, 2014 09:24PM
ok, Thanks for all the help!
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