3D Printer: Power and Electronics

Holiday and MozCamp have delayed the project a little, and I’m a touch behind on the blogging…

Every RepRap needs power and control. There are various electronics packages available for running a RepRap, designed by different people and optimized for different things. The electronics package I have is a RAMPS v1.4, bought ready-built off eBay from China. (In order to finish this project in 2012, I decided not to solder it myself from scratch…) Amazingly, it arrived before several parts sourced at the same time from the UK! It’s based on an Arduino, with a shield to contain the specialist electronics for running the motors etc. This means that it uses standard Arduino tools, and I can probably learn how to hack the firmware without too much trouble.

The PSU is a standard modern ATX PC PSU, modded as explained on the RepRap wiki. It turns out that PC power supplies are required, presumably for legacy reasons, to provide 3.3V, 5V, -12V and +12V power and, on some, -5V as well. Fortunately, all the wire colours are standardized. RAMPS just needs 12V.

The Mendel90 design had holes for a different electronics package and also had no mounting holes for the PSU, because they aren’t standard. So I had to plan and drill all these holes myself. I ended up mounting the PSU below, and the electronics above – with the power input cord and on switch on the bottom side, but the power wires coming out near the electronics. I needed to leave room at one end of the electronics to add the optional SD card reader without it sticking out in a way that means it could get knocked or damaged.

You can see from this internal view of the PSU that I have:

  • Added a power resistor (bolted to fan holes, lower left) to the 5V bus (red) to create a small load (some PSUs won’t start without it)
  • Wired the brown 3.3V sense wire to the 3.3V bus (orange; lower right)
  • Cut away most of the remaining wires (top right, behind the yellow and black ones; a standard PC power supply seems to have 40-50 wires coming out of it with various connectors)
  • Left behind 3 12V wires (yellow), 2 on one of the 12V buses (for the heated bed) and one on the other (for everything else), plus matching ground wires
  • The green wire is apparently some auto-on switch; it has to be connected to ground. Until I figure that out, I kept it full length and wired it into a ground terminal

2 thoughts on “3D Printer: Power and Electronics

  1. On a modern PC, the power-switch on the front of the case connects to the motherboard; the PSU also connects to the motherboard. The motherboard shorts the green wire to ground to control whether the computer is turned on – perhaps you hit the power switch on the front of the case, perhaps you picked your OS’s “Turn computer off” menu item, perhaps you have the BIOS configured to turn your computer on at a given time each day, that kind of thing.

    • Sure. I wasn’t clear; thing is, some boards (including my RAMPS) allow you to connect it to a pin so the electronics can turn on the PSU. This seems chicken-and-egg, but presumably you can do it when the Arduino part is powered from an alternative source, like the USB connection. I’m not sure if I want to use that feature, but I’m leaving my options open.