Prusa I3-RAMPS and ATX 2x4 connector

All:
I am pretty sure about the answer to this but I wanted to just double check with the group.

I am finishing wiring a Prusa I3 from Makerfarm. In the past I always bod bought 480W power
supplies and used the 2x2 connector and just two other black/yellow wires to power everything.

I found a great deal on a 550W supply on Amazon and so went that way. In any case, the
supply includes a 2x4 molex connector with just yellow and black wires (so all 12V).

I am thinking from some of my googling that this connector is high amperage and those 8wires
can power everything.

Anyone have any experience?

Should I split things even between the 11AMP and 5amp connectors on my ramps or should
I put 3 into the 11AMP and 2 into the 5 AMP?

Take a pic of all the non hard drive connectors and post it please.

Edited 1 time(s). Last edit at 09/05/2013 05:14PM by appdev007.

I also built the 6" Prusa i3 from Makerfarm.

I had problems with an old 400W ATX power supply I tried using at first (it had been sitting in an unopened box). Although it was less than the 450W the build instructions recommend, it claimed to supply 20A on both 12V rails. I believe this was not the case. It could never get the bed and nozzle both up to temperature for ABS (I am using 115C / 230C) even after an hour or more.

I ended up spending $50 getting an Antec Basiq 500W power supply from Fry's and it has worked flawlessly. I also ditched the recommendation to cross-connect the 12V rails since the Antec power supply clearly specified which wires were connected to which of the separate 12V rails (there was a sheet included with the PSU). Usually the separate 4-pin Molex connector is for "high-current" connections for video cards (the ATX spec is freely available from Intel) but off-brand manufacturers tend to cut corners on this (or so I believe).

Usually the 20 or 24-pin main board connector has 12V on a separate rail from the 4-pin or 6-pin Molex. At the same time I don't think there's any harm in cross-connecting (putting both rails on both sets of input terminals). I don't know enough about how the separate rails are implemented in switching PSUs to comment on whether that works as you'd hope.

See Wiki page for ATX spec and the latest ATX spec from Intel: ATX design guide

This isn't from 3D printing but I used the 4-pin version of the CPU connector from a Dell power supply (PSU) to deliver ~8-10A or so for a battery charger.

The video card connector (6 pin) is rated at 75W=6.25W@12V, and the 8-pin is 150W=12.5A@12V:
[www.enthusiastpc.net]

I cannot find the specs for the CPU version (that connector is not as well defined as the one for video cards), but assuming similar capabilities I would not do it. A lot of power supplies have a "multi-rail" design with current limiters attached to different cables: ususally the CPU connector (also nicknamed EPS12V) is on one "rail" along with maybe the hard drive connectors, and then the graphics card is on another rail. If you connect everything to the same rail, you could have the PSU shut down in the middle of a print. I recommend instead having the hotbed connected to that CPU connector and all the other stuff connected to the graphics card connector. If that 550W supply doesn't have both connectors, then it is a cheap unit that can't actually deliver 550W.

You'll want to get this one right. I was plagued by this issue for months. The PSU I had was of a name brand and stated it could do 16 amps on one rail and plenty more than 5 on the other, but it would appear it couldn't deliver. I had to add a 2nd PSU for the 11 amp connection before my issues went away. I'm pretty sure this was causing inaccuracy in motor steps and temperature readings. My prints increased by 25% when I added the 2nd supply.

All:
So I eventually answered my own question. Attached is a picture of the connector in question.
In addition it had the standard 4pin 12V connector and the long 20/24 pin one as well.
This is actually 2 4pin connectors that are hooked together.

In short when I first connected it I put two wires each on the 5A and 10A power inputs.
While things appeared to work in that the motors moved and the bed & hotend both heated
fine the real problem came when printing. Basically, as my extruder motor heated up
the extruder would miss steps and eventually I would stop getting filament out of the hotend.

I since re-wired and put 3 of the circuits on the 10amp and 1 on the 5amp. Things are now
working much better.

The appeal in using that one bundle is that I only needed to run the one bundle out of the
power supply and could stuff everything else back inside.