Building the C-Bot 3D printer: Part 3 : Power Supply Modification

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For this build, based on the recommendation of Mason, I picked up a Corsair CX 500 PC power supply from newegg.  500 watts of power, can do 38A at 12v (with a single dedicated 12v rail), so should be more than enough power for now, but room to grow.

Simple current calculations based on the biggest offenders:

  • 6x nema 17 steppers @ 1.68A (max) = 10.08A :
    • Core-XY mechanics, x2.  Z-stage. x2, Extruder, x1 (+ 1 extra for dual-strusion later…)
  • 12×12″ heated build plate : 20A
  • + other smaller draws.

After I got it he mentioned: “Oh yah, you’ll need to modify that too”.  Uh, what? :)

He pointed me to this great vid by MakerGeeks (I also like their (US made) filament), which shows you how to do the whole operation.

Highlights are:

  • Ground the green wire to trick the system into thinking there’s always a load.  Otherwise it won’t want to turn on…
  • Strip and plug the 12v wires/ground into your mainboard.

But this power supply has many bundles wires pouring out the side, far more than I’ll need.  I also knew this supply supported three different voltages, so after I hack-grounded the green wire using a paper-clip, I used my multimeter to check different colored wires:

  • Yellow : 12.46v
  • Red : 5.01v
  • Orange: 3.36v

Telling me, cut everything but yellow (and black).

So I got to work:  Opening the case, I isolated the green wire, and soldered it to one of  the grounds.  Heat-shrinked the result, tucked out of the way.

I need two separate lines of power out of the box:  One for the Rumba, and one for the HBP.  There were three bundles running out of the machine with yellow & black wires only:  Removing them from their protective mesh sleeving, I collected/connected (via twist & solder) three yellow/black for my HBP power, and another two yellow/black for the Rumba board power (could probably get away with one, I’m just playing it safe):  While the Rumba can power a HBP, it’s rated at 11A.  Since my monster 12×12″ HBP can draw up to 20A when heating, I need to connect it directly to the power supply (it’s temp will be controlled via a relay).  I choose to use three wires to visually match the gauge of the wires pre-soldered to the HBP.

Finally, everything else got chopped to about 3″ off the mainboard (in case for some reason I need to use them in the future).  I wrapped each end in electrical tape, wrapped the whole bundle in electrical tape, then clamped it down with zip-ties so nothing will come undone if things get hot.

I was very happy than upon reassemble it worked 😉  Next steps would be hooking it to the Rumba (which hasn’t arrived yet) and the heated bed.


Jump to C-Bot blog index to see all the posts.

Building the C-Bot 3D printer: Part 2 : Extruder Assembly
Building the C-Bot 3D printer: Part 4 : Cutting the linear rail
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