Quick Power Supply Question...

I've got an ATX power supply for my Prusa Mendel build. Does anyone have any instructions on how to wire this up to RAMPS/motors etc? Any build pics out there? Any advice or links would be appreciated

This might help you out: http://reprap.org/wiki/PCPowerSupply
Yellow is 12v, black is ground. You power it by grounding the green wire.

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-Nudel
Blog with RepRap Comic

Thanks for the advice, but I'm not willing to follow it and destroy $200 worth of RAMPS electronics to just "Try it" ya know what I mean? If anybody actually owns a Prusa Mendel out there and has an ATX power supply hooked up to it can you please post a pic of the connections? I'm a total buffoon with electronics

Edited 1 time(s). Last edit at 06/12/2011 05:12PM by anton zedd.

The "try it" part is just my tongue-in-cheek signature, pay no attention to it.

But yeah, basically you just need to supply power to the electronics via 12v and a ground connection. If you have a molex connector, you can make a fancy plug, if not you just cut off the needed wires and solder on extension wires if needed. (All with power off, of course).

Since ATX-psus don't have a on-off button per se, you start it by connecting/shorting the green wire in the big motherboard connector with a black/ground wire. There are plenty of guides on the net on how to do this.

I don't have the ramps board myself though, so there might be some precautions to take, which others are sure to fill you in on.

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-Nudel
Blog with RepRap Comic

Thanks, I really appreciate the help.

Most PSUs do have a power on/off button on the backside. I think the easiest way is to connect the green and ground permanently and use that to turn it on and off. Make sure to short the red & black together before working on it!

The power supply has one connector in particular that has four prongs. Two black, and two yellow. Use these, as they provide the most amps. You can tie the matching pairs together. Remember that Yellow is (+)12vdc and Black is (-)GND.

If you want to tidy up the power supply, you can open up the case and snip off most of the other wires. The only other thing you need in there is to tie the green wire to another black wire, or solder it to GND. I kept an extra Orange (+3.5vdc) and Red (+5vdc), and added banana plugs on the outside.

Mine is a 450W ATX, with 28amps on +12, and powers a heated bed as well with RAMPS.

jcabrer Wrote:
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> The power supply has one connector in particular
> that has four prongs. Two black, and two yellow.
> Use these, as they provide the most amps. You can
> tie the matching pairs together. Remember that
> Yellow is (+)12vdc and Black is (-)GND.
>
> If you want to tidy up the power supply, you can
> open up the case and snip off most of the other
> wires. The only other thing you need in there is
> to tie the green wire to another black wire, or
> solder it to GND. I kept an extra Orange
> (+3.5vdc) and Red (+5vdc), and added banana plugs
> on the outside.
>
> Mine is a 450W ATX, with 28amps on +12, and powers
> a heated bed as well with RAMPS.

Do you recommend running two sets of yellow/black for the 5A electronics (RAMPS) or is 1 enough? The wire is 18AWG. Thanks

Edited 1 time(s). Last edit at 07/06/2011 09:11AM by loheiman.

One set of wires should be plenty for 5 amps. If you end up adding a heated bed, you'll probably want fatter wires for that circuit, otherwise it'll take forever to heat up.

raldrich Wrote:
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> One set of wires should be plenty for 5 amps. If
> you end up adding a heated bed, you'll probably
> want fatter wires for that circuit, otherwise
> it'll take forever to heat up.


I think i'll bundle 2 or 3 sets of wires for a heated bed if/when I get one. Thanks.

I run two pairs, from the mentioned connector.

There is a really nice instructables article that has an easy way to convert a PSU to a lab bench PSU.

As for the heated bed, I use the Red PCB Prusa Heated Bed, and I connect one wire to the (-) on D8, and the other to (+) on the RAMPS 12VDC Connector. See the attachment for details.

With so many +12 and gnd wires coming out of the ATX power supply, it's better to use all the wires in that connectors so that you have 2x +12V and 2x GND wires to supply the heated bed with power. You can take the RAMPS supply from another connector. The heated bed alone can take as much as 12A of current which would require 2 wires, not one.