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Need help connecting PSU to ramps.

Posted by Drangid 
Need help connecting PSU to ramps.
March 18, 2013 12:11PM
Hello all,

I'm a total newbie with electronics, so I apologize if my terminology is off.

My kit came with an ATX PSU and I am trying to connect it to the ramps 1.4. I cannot figure it out through the wiki or tutorial videos. My ramps board does not have a molex connector, but instead has a mosfet terminal. Should I be cutting off the molex connectors from my PSU and sticking them into mosfet slots? Which wires should I be using? When I see the following image:


I get the feeling that I want to cut and use the wires from the 4 pin (2x2) molex connecter because it has 2 black and 2 yellow, and then fasten them into the mosfet labelled 11a/5a, but I don't want to assume this. I also don't know what the L, N and G labels are.

I'm actually getting the sense that a ATX PSU isn't appropriate for this at all. I'm also uncomfortable making these connections. I have access to a 12v 200w power supply: http://www.a2aprinter.com/index.php?route=product/product&path=33&product_id=53. I am attaching a heated bed, and the product description on this 12v power supply mentions that. The heated bed was optional with my kit, should I have gotten the 12V power supply instead of the ATX?
Re: Need help connecting PSU to ramps.
March 18, 2013 01:02PM
You cannot follow that rampswire14.svg picture to wire the system. Instead you can follow this: [www.wikihow.com] and then just connect 12 V and GND to RAMPS. Note that both 12V and GND have two terminals in RAMPS, you can just jump wire the other pair.

Alternatively if you do not want to open the PSU, you can take orange 12V and black GND wires from PSU wire harness, and connect them to RAMPS. Then take green wire in the big motherboard 20/24 pin connector, and short it to ground. Your PSU should then give power. You should also have some load on 5V (red) line, a 5-30W 5-12V bulb will do fine.
Re: Need help connecting PSU to ramps.
March 18, 2013 02:33PM
Thank you, jkoljo

I'd prefer to go the route of not opening the PSU. So going with the altnerate, which wire do you mean by orange 12V? I'm seeing all oranges labelled as 3.3v in the diagrams. Can it be one of the wires from the 24 pin connector? And I don't know where you mean by the wire harness.

If connecting those to the RAMPS, do I have to "jump wire" to the other pair of 12V+GND as you mentioned in the first method, and how do I do that?

Shorting the green wire is just a simple matter of sticking a piece of metal into the 24 pin connector onto the green wire, and connecting it to a black one, right?

Sorry for all the questions. As I say, I don't know anything about this stuff. I actually didn't think it would have required this knowledge or skill, I thought my board would come with the compatibleconnectors for the PSU. Would the other power supply, the 12V, work better because I could just connect wires between the supply and the ramps without having to figure out what wires to cut?
Re: Need help connecting PSU to ramps.
March 18, 2013 06:54PM
Sorry mate, I really should not be answering questions in forums when tired.. I mean Yellow for 12V. My bad. And yes it can be from the big 24 pin connector.

You are correct about the green wire, you can just add a piece of metal. I still recommend soldering and using heat shrink tube smiling smiley

The point in jump wiring is that RAMPS takes 2x 12V+GND, and you want to connect all terminals. So if you wire 12V+GND to one terminal pair, you can just add some short wires from those terminals to the other terminal pair. You can also take all wires from the PSU, it has enough wires for the job (and plenty more).

The 12V 200W power supply is not big enough for a reprap with heat bed. It should be enough if you forget the heat bed.

Edited 1 time(s). Last edit at 03/18/2013 06:58PM by jkoljo.
Re: Need help connecting PSU to ramps.
March 21, 2013 05:14PM
I had a power supply like yours and I did not need to do the resistor on the 5v rails - I just hooked the 12v yellow to the + in, and the black to the -.

Shorting the green to black as you suggest will work. An easy upgrade is to hook the green wire to the "PS_ON" pin (it's next to the reset switch on the RAMPS board - take a piece of wire from PS_ON and hook it up to the green wire from your power supply.

You can then turn your power supply on and off with M80 and M81

For information (doesn't really apply anymore, but info is never bad) L-N-G from the original image is the power from your wall outlet - line neutral and ground. This is the same as the power cord plugging into your power supply.
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