I'm reading about wiring up the electronic components to my Prusa i3 using an Arduino Mega 2650 and Ramps 1.4.

I have step sticks, a heated bed, and a Switching Power Supply 12v Dc 30a 360w (more details on that later when I can add which ones to the post).

I've heard that if you wire it wrong and plug it in, you can do anything from starting a fire to burning out your boards.

What are some tips of things to check before plugging it in? Are there any common mistakes that I can avoid?

  • $\begingroup$ I've actually got this question elsewhere too (arduino.stackexchange.com/questions/18810/…), but I was planning on using a different power supply at that point, so do with it what you will... $\endgroup$
    – leeand00
    Jan 13, 2016 at 16:51
  • $\begingroup$ Not really an answer, but ALWAYS DOUBLE CHECK all wiring before plugging anything in. $\endgroup$ Jan 14, 2016 at 4:48

3 Answers 3

  • Polarity matters, sometimes. Be especially mindful of the wires from your power supply to the board, as getting those the wrong way around will definitely cause damage. Heated beds and extruders are not polarity sensitive, and can go in either way. Fans are polarized, but will probably survive if you get them backwards - they just won't run. Stepper motors don't care about polarity, flipping the connector around just makes them run backwards.

  • Take special care with endstops. The endstop connectors have 3 pins (VCC, 5V and signal), endstops with 2 pins are usually connect to GND and signal. Putting a 2-pin endstop across 5V and GND will destroy the 5V regulator.

  • A common cause of damage is wires not being clamped in their respective terminals properly. The offending wire will arc, melting and destroying the connector. Tighten down screw terminals properly, use proper crimps if you have them. Soldering the ends of wires going into screw terminals is not encouraged, but if you do solder the ends then make sure to check after a while and tighten the screws again.

  • Put the stepper drivers in the right way around.

  • For things like the heated bed and wires going to your power supply, use sufficiently thick wires. Especially with the heated bed, a lot of current flows through the wires and flimsy wires will heat up and melt.

  • $\begingroup$ Good points! Why would soldering wire-ends going into screw terminals not be encourage? I always do that to avoid loose strands that could slip out and short... Though I agree that one should re-tighten. $\endgroup$
    – TextGeek
    Jan 13, 2016 at 17:12
  • 1
    $\begingroup$ reprap.org/wiki/Wire_termination_for_screw_terminals $\endgroup$ Jan 13, 2016 at 17:14
  • 1
    $\begingroup$ @TextGeek use a cable-end sleeve (ferrule) instead. $\endgroup$ Jan 13, 2016 at 17:18
  • $\begingroup$ @TomvanderZanden My endstops for some reason have 4 connectors! 3dprinting.stackexchange.com/questions/1478/… $\endgroup$
    – leeand00
    Jul 7, 2016 at 17:21
  • $\begingroup$ > Putting a 2-pin endstop across 5V and GND will destroy the 5V regulator. I think I've done this... at least I made some magic smoke. Would the regulator be on the arduino or Ramps board? How to test if it is dead? Thanks. $\endgroup$
    – Lemmy
    Dec 15, 2018 at 18:47

I'd say polarity and voltage are the biggest things -- about all you can do is double- and triple-check everything; then check again....

Be very careful about where you feed in 12V power (mainly for heaters and fans), vs. 5v (for the Arduino).

In many cases I found it unclear which way +/- went going out from the board (the inputs on my boards were at least marked clearly!). I found that if I plug in a limit switch connector backwards, that connects 5v straight to ground, which will probably make your power supply cut out (assuming it's properly protected -- otherwise it could potentially catch fire). Stepper motors, on the other hand, just run the wrong direction if you plug them onto RAMPS backwards (good design!).

Another thing to watch for only comes up if you're powering the Arduino via USB (I do that a lot, since I'm plugged in anyway to send files and such). A short can try to draw too much power from USB. In that case my Mac shuts down USB and gives a message; I don't know what would happen with other hardware.

I have heard that plugging a stepper-driver board onto RAMPS backwards is likely to fry a board, and that plugging or unplugging a stepper motor while powered is also risky. But I haven't messed those up yet, so I don't now for sure. :)

I may be overly cautious, but I never leave the power supply plugged in when I'm not around.

Best wishes!



Adding to the other answers:

  • ALWAYS power-off the printer completely and make sure it is not receiving any power from any source (could be receiving power from USB after you turned the power supply off).
  • Avoid loose wires, and before powering the printer on make sure every wire is connected in the right place. Loose wires can cause damage even if not powered if they get under the PCBs, where they can cause shorts. I fried an Arduino Mega this way.
  • Never mix between 12v and 5v supply/output wires. Connecting an output wire of the wrong voltage will usually cause damage only to the part receiving power, while connecting a supply wire of the wrong voltage can cause severe damage to many components at once.
  • Keep all wires organised. That will help you understand which wire is connected to what quickly, and will help you do what is mentioned in #2 and #3.

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