P3Steel Build Log (#16) – Power Supply and Core Wiring

By ChunkySteveo,

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The 3D Printer Power Supply (PSU)

Now that we have all the stepper motors in place, we’re slowly getting there! If you’re following along this build log – you may be wondering when I’m going to get to the hotend assembly. Well – that was a huge job and the write up is going to be even bigger. So I may or may now have followed these steps in order when building, but it doesn’t matter too much! On to the power house, the power supply unit, or PSU.

I wanted a beefy supply which was capable of supplying enough amps for two extruders if and when I may or may not upgrade my machine. So a 12V 30A supply was bought. I also went with the classic “thin” style PSU which are commonly used for LED lighting, rather than an ATX style computer PSU. The link to the actual supply is here – http://s.click.aliexpress.com/e/uBQ7qz3, but it’s no longer available. The seller Geek World comes highly recommended though, and they have an alternative listing for a 360W PSU here – 3D Printer 12V 30A 360W PSU.

The PSU has three 12V rails to attach to, and comes in a standard (for 3D printing and LEDS!) form factor. What you don’t want though is a PSU left lying around with mains voltage hanging out of it, and 12V connectors easy to reach with fingers, screwdrivers, metal, tongues…. 😝 etc. I also wanted to be able to switch the printer supply on and off with a convenient switch, and for the mains power to be connected safely, securely and consistently – with a common IEC 3 pin power connector.

Behold the finished PSU and PSU cover, printed in my standard orange. I would show you the 3D timelapse, but it looked so bad, it looked like it was filmed in the Bat Cave!

IMG_7148 IMG_7150

So the PSU cover prints wih two holes, one for a standard IEC C14 male plug 3 pin connector (http://s.click.aliexpress.com/e/ni2ZBiu) and a beefy power rocker switch with illuminated LED (http://s.click.aliexpress.com/e/NnAmyZj) so I can see it’s powered up night or day. The rocker switch just snaps in, and the IEC 3 pin connector screws in with a couple of M3 bolts. The bolt threads just screw into the PLA plastic and secure it really well. If you have other requirements, or fancy using an integrated 3 pin plug connector, fuse and switch – there’s lots of options on Thingiverse for you to print out.

Wiring up The PSU

I will not go into detail here, as it all depends on what hardware you are going to use as per above – switches, plug connectors, inline fuses etc. I would have liked an additional fuse, but couldn’t find space for it. All I will say though is take this step extra slow – read up on LOTS of tutorials, guides, videos and advise as you are now working with MAINS AC connections. Shoddy wiring, incorrect wiring and bad connections WILL lead to faults, shorts, fires and possibly DEATH! ☠️ Do not mess around at this point of cut corners!

The path I went down to wire up my PSU was to use an unused power cable, strip it down and use the existing live, neutral and earth wires to wire up the IEC 3 pin plug connector, to the switch, and then to the L, N, E connectors on the PSU. I used spade connectors rated for the gauge of wire and shrink wrapped all connections with heatshrink wrapping.


The reason for the warning above is that if your solder joint is weak or you have insufficient solder to deal with the amps pusing thorugh it will heat up and possibly de-solder. A de-soldered joint will short, spark and potentially cause a fire risk or electrical shock. With connectors that are crimped to the wire and connected using spade connectors, there is no chance of them melting or coming loose. You can sleep safe(r) at night knowing the PSU will not short out, catch fire or cause you a shock.

Rant over, see my wiring attempt below: (left is the plug connector, middle is the rocker switch, which then sends the power up to the PSU).


Test your PSU with a suitable 12V device, such as a strip of 12V LEDs or a multimeter on one of the 12v rails. They (LEDs) should light up, the rocker switch should isolate the supply, and if your PSU has a fan on it, it should get louder with the increased load. Once you are happy, you can test fit it to the frame. For the P3Steel, this is usually fitted to the other triangle frame upright, in whatever best solution you can find that fits your PSU and it’s mounting holes. You will want to have easy access to the plug connector, and with my design I used, the power cables which will go to the printer will come out the bottom as per the example image above – which will be nice and safe and out of finger (tongue) reach.


Lets assume you you have gone for a PSU like above, or purchased the one in the link further above. They tend to have some mounting screw holes which will accept M3 bolts. It’s a case of lining up the PSU with the frame and seeing where these mounting holes line up with the holes within the frame. I was able to line up a lower and upper mounting hole with two of the “circular-rectangle” holes in the frame. To secure the PSU to the frame I used a couple of oversized washers to cover the holes, and screwed in some M3 bolts. I do plan to make some plastic parts for this job, but all in good time!


The Core Wiring For the P3Steel 3D Printer

Now that you are happy with the placement and fastening of the PSU to the frame – take it off(!) We now need to wire up the main core wiring which will power our printer. This is the core power feed from the PSU to the RAMPS board and will power the entire printer. Power supplies to the motors, heated bed, extruders and Arduino etc all come from this main feed. And RAMPS is designed (not very well – heated bed!) to take in two power sources and distribute them throughout the 3D printer. You will see on a RAMPS board a four way green connector, or two x two connectors. The lower connector (if looking at the board with the green power connector at the lower left) is for main board power and for motors etc and this takes up to 5A. The upper connector is for the heated bed, and can take up to 11A. Keep an eye on that top connector as the RAMPS boards tend to be built with cheap components which cannot deal with loads upto and over 11A…. and melt!


Anyhow, enough scaremongering. First we need to get the power from the PSU to the RAMPS board. As one line will be bringing over 10A we need some beefy cables – again, this is where you should not be cheap, and get some thick quality cable which is capable of taking the load. A rough suggestion for you is it use 14AWG wire – which is capable of taking upto 15A at a distance of 45 feet. We will need less than about 1 meter of cable, so this will be more than enough. You could go smaller (and hence a higher AWG number), but it’s cheap enough and will last the test of time. I got two 3m lengths of 14 gauge AWG wire on AliExpress here –  14 gauge awg wire. It’s great stuff and super chunky!

IMG_7241 IMG_7243

Think Ahead – Quick and Safe Isolated Connections to the PSU

This step is optional, but I would highly recommend it.

You can just connect the core wires from the RAMPS board to the PSU terminals, no problems. But you may change the location of the board or PSU some day, or swap out something further down the line, or need to physically isolate and disconnect the power cables from the PSU. To disconnect the wires you would need to remove the PSU from the frame, unscrew and plastic housing and then unscrew the terminal blocks. It would be a lot simpler, quicker and safe if you had a dedicated connector within the wire to just unplug…. right?

XT60 connectors

Image from Sparkfun

To do this you will need a connection sufficient enough to handle the power. You have just clicked on the link above to go buy the 14 gauge AWG wire right – you wouldn’t then use a mini JST connector or a 2 pin dupont connection right?! In steps the XT60 connector – a dedicated connection standard which is designed to be used to connect to batteries and high loaded cabled. They are used a lot in remote control planes/cars etc and are designed to take up to 60 Amps and their connections are suitable up to 10 gauge AWG.

You can get a set of these from the following link, i’d highly recommend them! XT60 connectors.

Once we have the connectors you will need to solder one end of the core wires to them, and then solder on another shorter set which will go from the connector to the PSU terminals. This length I leave up to you – but it need to be long enough to allow the connectors to be visible and accessible outside the PSU cover, but not too far from it. To solder the 14 gauge AWG wire to these connectors you will need A LOT of solder. These chunky gold plated connectors allow for a thick and solid interface between cable and plug. Follow some great tutorials on YouTube which show you how to solder these. But you will need some hleping hands (As they get very hot), tin the wire, prime the connector connections with a lot of solder and then heat them together.

Top Tip is to leave the connector parts together to help dissipate heat away. Another top tip (AND A GOOD ONE) is to use the female connector as the side that will be permenantly connected to the PSU. If you have to leave it disconnected for some time – the positive and negative points will still be live. A stray piece of metal or finger could get into the “male” connector and short this gap – whereas the “female” side are housed in plastic and there is less chance of these two connections bridging accidentally! Think safety, always!

After the short cables are soldered (to the female part) you will need to crimp on two ring type spade connectors to the ends. This is where we will attach them to the PSU terminals, which are screwed in. Don’t forget if you’re using a heated bed you will need two core cables, so as per the image below you will need two of everything. Don’t forget to keep everything neat and tidy and safe with some heat shrink.


You can roughly lay out the cables from the PSU and trace them under the printer to the RAMPS board. This will give you a good idea of length to cut, now that you have the connectors in place. A rough guide would be 1m of 14 gauge AWG wire per cable. This will be more than sufficient and give you room at the end to trim them down. Be more accurate if you have less cable to spare. Now lets solder the other end of the XT60 connector to the newly cut cables. Again – don’t forget to keep it neat with some heat shrink. You should have some cables that look like below. Leave the other end raw for now.


This next step is also optional – but you really should protect and manage your cables from the start. I wrapped my power cables in nylon braided cable cover (https://www.aliexpress.com/item/Free-Shipping-10m-8mm-Dia-General-Wire-Protection-Black-PET-Nylon-Braided-Cable-Sleeve/32431717400.html). I couldn’t find any good looking orange and black style, so went with just black, It grows and contracts to fit your needs, can take up to 10mm in diameter of cable, and can be cut to length. It’s at the limit with two (positive and negative) 14 gauge AWG cables. To stop it from fraying at the ends I always heated it with a flame and then coated it in large black shink wrap, as per below:


Next up is to connect one end to the PSU. So take if off the frame if you haven’t already – it will make you life a lot easier! Then unscrew the plastic cover to reveal the terminals.


You will need to check your PSU wiring to see which are the positive and negative terminals. But usually (as per above image) there are three positives on the left, and three negatives on the right. (Then the earth, neutral and live from the AC mains). I don’t think it matters if the positive and negative match up (i.e in 1 and 4, or 2 and 5 etc) – but to keep it neat and easy to understand, you should keep them matched so the first cable is in terminal 1 and 4, second in 2 and 5 (as looking from above). Once you have securley fastened down the cables to the terminals and screwed back on the plastic cover, you should have something that looks like this:


Routing The Core Power Cables For The P3Steel 3D Printer

Before fastening the PSU back on to the frame – feed in the power cables into the frame via the holes available. You can route this how you like, but ideally you should route it out of the way, and away from any moving parts. Two sets of 14 gauge AWG cable and sleeve just fits through the little holes in the frame. You can see where I routed the cables below.

IMG_7251 IMG_7253 IMG_7254

I will cable tie up the core wires to the frame with the holes available to keep everything neat and secure. Next is to cap off the other end to connect it to the RAMPS board.

Usually the RAMPS board comes with a connector that will come away from the board.We need to connect up the two wires to this connection.


Follow the silkscreen print on the RAMPS board, and see the images below as reference. If looking at it face on – the core wires need to go negative, positive, negative, positive from the bottom up..Butt up the wires to the terminal blocks and screw down the fasteners until the cable is tight and does not come out.

IMG_7256 IMG_7260

Now – if you can – get good end connectors for the cables and crimp them in. Using the bare core is not good practice, and I WILL be upgrading this part!!

Your printer now has POWER!!



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