Now that you are done, or close to being done, with you 3D printer, you need to get it some power! You can do this buy either purchasing a power supply that is agnostic to what it powers, like a switching power supply that just has screw terminals to attach whatever you need to or you can hack up a power supply to repurpose it for your 3D printer. The latter is usually much less expensive, especially if you have something sitting around already and sometimes they can be more reliable.

If you choose to repurpose a power supply, you can salvage them from anything from computers to video game consoles. These power supplies either come in the form of an ATX power supply, which is what you typically find in the big towers of computers, or “power bricks”, which are exactly what they sound like, a big blocky thing that supplies power. We picked the power brick because they typically have a connector that has everything in it already that we need to make operate; power and sensing lines. So, they’re very easy to work with!

The Dell power supply we picked usually comes with the Dell Optiplex series desktop and supply quite a bit of power. If we check out the label on this guy, it says, right next to output 12V and 18A. This means that the maximum output of this supply is 12v @ 18 Amps, which is plenty and is a total of 218 Watts.

IMG_20121219_162802Now to take this thing apart and make it a power supply we can use!

So the top down view of this thing; theres the body and the cable running out with the connector at the end. That’s what has all of the wires that we want to get at.IMG_20121219_160652The first thing we want tot do is snip off the connecter as close to the base as possible, this will give us plenty of wire to play with.IMG_20121219_160848



Now that we have the connecter off, we want to take off the jacket, the rubbery thing covering all of the wires, down to the big choke that’s on the cable. You should look like this when you’re done.IMG_20121219_161015Now, you should see 3 White wires, a blue wire, a red wire, 3 black wires, and a wire that doesn’t have any jacket on it at all. They are….

  • White – 12V+
  • Black – 0V (GND)
  • Blue and Red – Sensing
  • Un-jacketed  – 0V (GND)

The white 12V rails are the wires that you will be putting into the terminals we marked “+” and the black 0V rails will be going into the terminals we marked “-“. DO NOT FLIP THE POLARITY!! VERY BAD THINGS WILL HAPPEN. I recommend tying all of the white wires together and the black wires together so that your connections will be clean. I’ll show you what I mean in a minute.

So, now what do we do with the wires besides the white and black? The red and blue wires are used to turn the power supply on by connecting them to 0V, we will use the un-jacketed wire. Right now if you were to plug in your power supply, the indicator light on top would be glowing kind of orange/yellow. This means your power supply is in standby and not supplying any power.IMG_20121219_161054

Now, strip off some of the jacket on the red and blue wires. If you have an alligator clip, connect them together and then to the un-jacketed wire, like so. If you don’t have an alligator clip, just twist all three of the wires together so you have a connection. NOTE: This is never ok to do in practice, we’re just checking things out right now. You should ALWAYS make secure and insulated connections. IMG_20121219_161141

After connecting the blue and red wires to the un-jacketed wire, check out the light on top of the power supply. It should be glowing green! That means we have power! Now, wasn’t that easy? If we take a multimeter and check the voltage across the white and black rails. We should have about 12V with no load.

Look at that! 12.4 Volts!

Now, we want to tie and solder all of the rails together into a single wire. Once, we do this, we can then make a short “jumper” wire that will connect into both the terminals for   “+” and “-“. First we’ll tie and solder the rails. For your other wire (the one you’re soldering to the rails from the power supply and the jumper) use a either 16 AWG or 18 AWG wire. These are a little bit bigger (thicker) wires that can handle more current without a drop in voltage.

Before you solder the rails to your wire, make sure you get a good physical connection as well. A good wrap like this will be plenty. It may not meet many standards or regulations for splicing, but for our application it will be plenty.


Put a nice insulator around your new splice. You don’t want that shorting out on something. Sparks are bad.

Do this again for the 0V rails (the black ones).  After this, you should all three white 12V spliced together to a single wire and all three black 0V rails spliced together to a single wire.

The wires you should have left over are the blue, red, and the un-jacketed wire. These we are going to use these wires to turn on and off the power supply. By tying the red and blue wires to 0V the power supply comes on. Later, we’re going to connect these to a single-pole-single-throw switch (this is the switch that came in the kit we provided you). To get ready for this, we will splice the red & blue together to another wire like below. Make sure the wire you’re splicing to the red & blue wire is long enough so that you can position your switch where ever you want later. Don’t forget to insulate the joint with something after you solder it.

Make sure you get a good physical connection before you solder the joint.

Do the same for the un-jacketed wire with roughly the same length of wire that you spliced together. Make sure one you finish with the splice that you insulate the full length of the un-jacketed wire. It’s never good to have an exposed wire.

Now, you should have the red & blue wire spliced into a single wire, the un-jacketed wire spliced to wire of the same length as the one spliced to the red & blue wires, and wires spliced to the black & white rails. Now, if you have switch (like we mentioned earlier) we’re going to solder that up. If you don’t, you can get by using alligator clips or something to connect the un-jacketed wire to the red and blue wires.

If you do have a switch that is single-pole-single-throw switch, there should only be two terminals on the switch and only two postions the switch can be in. It should look something like the photo below. Yours may not look exactly like this one…

A single-pole-single-throw switch should only have two terminals and only two positions or states that the switch can be in. Those two positions either make a short between the two terminals or has them unconnected.

We are now going to connect the two wires from the red & blue wires and the un-jacketed wire to the two terminals on the switch. The wires should look something like this before you solder them. If you have too much exposed wire hanging off the terminals (like I do here) you may need to trim some off. It’s a good idea to cover any exposed wire or terminal with heat shrink or electrical tape.

The two wires connected to the terminals of the switch will either be connected or unconnected depending on the position of the the switch.

Lastly, we need to wire up the terminal connector for the RAMPS board. It is extremely important that this part is done correctly. If you wire up the polarity wrong, you will destroy your board. Bad news. We’re going the put a jumper across to make each “+” and “-” terminal common to each other. To do this, we need to make two jumpers.

Start by taking two shorter pieces of wire (thicker ones) and stripping off the jacket on both ends. Just like below.


These two jumpers will be used to join all of the “+” terminals and “-” terminals together, respectively.

To keep the ends of these stranded wires from coming apart, we are going to “tin” the ends. “Tinning” the ends of the wires means that we are going to put some solder onto them. They should look like the photo below when you’re done.

Tinning both ends of this stranded wire help keep the ends from falling apart and the individual strands of wire from breaking.

Now, put it all together in the terminal connector. Make sure to get the right polarity in the right terminals. Shown below is how to connect the main wire from the power supply and the jumper going across. Do the same for the 0V wire in the correct terminals.

IMG_20121220_232150 (1)
Insert the wire from the power supply and one end of the jumper into one of the terminals. MAKE SURE IT’S THE CORRECT POLARITY! Then connect the other end of the the jumper wire to other appropriate terminal of the same polarity. Do the same shown here for the 0V rails.

There you go! You should be ready with power. Just flip the switch and you should have 12V!



6 Responses

  1. Great instructions.
    I need to buy the female terminal block, right now I’m using an short piece of wire with some extra crimps from the psu.
    Also I found the connector did not fit a standard computer molex adapter.

    About how much current does the printer use when printing? I know the heater uses around 1.4 amps, but how much do the stepper motors consume?

    1. If you purchased a full RAMPS kit from somewhere, the terminal block going into the RAMPS should be a two piece pluggable terminal block. Ultimachine sells them here

      What connector do you mean? The one that we remove? The connector we remove is a proprietary design for only Dell computers. You may be able to find a female connector for it, but I doubt Molex manufactures one.

      A better question is how much current will the printer draw when “cold”. Meaning when the heated bed and nozzle is still trying to heat up. If you have a 12V power supply the bed can draw about 8 amps and the nozzle will draw about a little under 2 amps. Your printer will probably be drawing the most current at this time. If you can get a power supply that can put out around 15-20 amps at 12V, you’ll be able to get by.