Hi Guys, long time lurker here. Anyhow I started building a Prusa I3 inspired 3D printer a little bit ago and have finally come to the power supply. So we had some pretty high end desktops my work was recycling and I managed to snag a PSU from one, Model number (Dell) N750P-00. Do you guys think this would work for a Prusa I3?

That will work fine as well as offering plenty of power for expansions later on such as multiple extruders. 700 watts is plenty to run both the 5 amp and 11ish amp circuits on a typical ramps board.

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Prusa i3 Rework - Ramps 1.4 - E3d Lite6 - Full Graphic LCD Controller

Cool Thanks! Yea based on what I had read it seemed like the PSU would work, I just wanted to confirm with some more experienced opinions.

Just make sure you put a load on the 5V and 3.3V lines. ATX supplies can have stability issues if you only load the 12V line.

One string of the four 12V lines can deliver 18Amax.. That would be enough for an average printer. But keep in mind that the cable diameter might be on the thin side. Voltage drop is one reason for problems, when you want fast heatup or reaching temps at all.

-Olaf

The PSU is currently at work, I will check the cable diameter when I get back. I assume I could just bundle two of the 12v rails and grounds (two separate bundles) and have the heavy gage wire coming out of those for the respective ground and 12v connections on the ramps board? That would essentially give me 36 amps to work with at 300 watts. I am a newby at electronics so feel free to tell me if im wrong here.

What would be the best way to put a load on the 3v and 5v lines?

Edited 3 time(s). Last edit at 09/05/2015 04:20PM by wmans.

Yes, that will work. Hooking them up in parallel (the way you described) will add their amperage together.

I have a 750w server power supply that has 5 separate 12v rails as well, as well as a protection circuit that will shut the PS down if you overdraw a rail. I have one rail going to each of the two RAMPS power inputs, and two rails wired to my bed heater (if I only connect one it goes into protection mode, as it pulls 20-25W), and the 5th rail just runs my fans.

As for loading the 3.3v and 5v, maybe LEDs?. Though, if being underutilized is the problem, I don't know if a few LEDs will drawn enough juice. To be honest, I've never really put much thought into that, since I just clipped those connections off my PS, and it hasn't caused me any problems so far. Even if it's bad in the long run, I'm not too worried about it. I have several hot-swappable spares. (That's not an endorsement, just a personal observation. Putting a load on the 3.3v and 5v lines seems like a smart idea.)

LEDs are not the best choice for a load. They require an dedicated inline resistor.
Parallel wiring the rails work, as already mentioned.
Some people use 12V( 20-50W ) halogen light bulbs as load. You have to find a suitable socket and a secure place to mount them.



-Olaf