I want to run two stepper motors using Arduino Mega 2560 and RAMPS 1.4. But, somehow I burned the Arduino while I was connecting the motor and plugging the board to the computer.

Can I plug external power supply and USB connection to the computer at the same time?

Additional info from comments

I am using RAMPS 1.4 with Polulo red stepper drivers and Arduino Mega R3. I am only using two Nema 17 stepper motors and not using any hotbed or anything else other than the two stepper motors for the x and y axes. I am feeding 11.9 V supply to the RAMPS board. When powered on, can I plug the USB to my computer?

Suppose I have connected two motors on the X and Y outputs of the RAMPS, and the external power supply is on, then can I connect my Arduino to my PC using USB? Will it burn my board or not?

My only trouble is that when the board is on load, connecting the USB to computer motors would take power by Arduino pins instead of the RAMPS external supply.

  • $\begingroup$ This question would be better suited for the electrical engineering or arduino sites on stackexchange, as there is really no specifics for it being a "3d printing question". $\endgroup$
    – mac
    Apr 7, 2018 at 0:12
  • $\begingroup$ I think this is an electrical engineering question, but it seems to be an EE question within the context of constructing and troubleshooting a 3D printer. As an EE, there is no specific problem with what you tried, provided that all supplies are properly isolated. Before burning another Arduino, reconnect the parts you have now one at a time, check for unexpected voltages. In particular, check that the ground levels are at zero or near-zero potential difference before connecting. Also, be sure that all grounds are tied together. The motor supply ground must be connected to logic ground. $\endgroup$
    – cmm
    Apr 20, 2018 at 13:27
  • $\begingroup$ <continued> Grounding is a large subject, and someone will justifiably pile onto this answer with concerns about ground loops and noise, but if your grounds are not common, you risk sneak paths and destructive voltages when you interconnect systems. $\endgroup$
    – cmm
    Apr 20, 2018 at 13:29
  • $\begingroup$ From your comment about D1, and looking at the link provided by the Professor, it states D1 should only be installed if the 5A rail is powered by 12V. It can be omitted and the Arduino will be powered from USB. You will want D1 installed if you add components to print without a PC. To reiterate, D1 MUST be omitted if you are powering the 5A rail by more than 12V, or the power is not absolutely clean, otherwise you may damage your ramps. $\endgroup$
    – Greenonline
    Jul 31, 2020 at 5:11

2 Answers 2


I had a similar issue building my Prusa i3 Mk2s clone. I was constantly hooking & unhooking my Arduino from my PC while the printer was plugged into the mains. At some point it had enough & it released some "magic smoke". Later on I found out this was the power regulator on the Arduino.

You shouldn't need to plug in the USB and the external power to the Arduino at the same time, but if you did, it is smart enough to only use one.

That being said, by default the RAMPS passes 12V straight to the Arduino in order to power it (the Vin pin).

  • 1
    $\begingroup$ now i fixed the problem.actually the diode d1 was creating that problem. $\endgroup$ May 8, 2018 at 4:27
  • 2
    $\begingroup$ i removed the diode d1 now everything is working good. $\endgroup$ May 8, 2018 at 4:28
  • $\begingroup$ @sandeepkumar - Hi Sandeep, could you post an answer stating that the problem was solved by fixing the diode D1? To do so, please flag the question for re-opening or leave us a comment - that way we can re-open the question for you to be able to post the actual solution as an answer... It may help someone with the same problem. Many thanks. :-) $\endgroup$
    – Greenonline
    Jul 31, 2020 at 5:06

The answer is, yes you can, but you need to follow guidelines.

Reversing +/- or otherwise incorrectly connecting power can destroy your electronics and cause fire hazard.

From RepRap wiki - RAMPS 1.4

Maximum Input Voltage Power Supply without diode There are three limiting factors to the maximum voltage that you can put into the RAMPS:

The Arduino Mega maximum input voltage Filtering capacitor maximum voltages PTC fuse maximum voltages First, the 1N4004 diode connects the RAMPS input voltage to the Arduino Mega which has a recommended maximum input voltage of 12 volts. If your board does not have this diode soldered in (or if you cut it), you will need to power the Mega through the USB connector or through a separate 5v line, but this allows a higher RAMPS voltage.

Second, most boards use 25v or 35v aluminum electrolytic capactors (C2, C3, C4, C6, C7, C9, and C10). To be safe, you should only go to half of your rated maximum voltage -- thus if your board has 35v capacitors (code VZA) then you should use a maximum input of 17.5v. The absolute maximum voltage is determined by the pololu servo drivers, which themselves are limited to 35V.

Third, the MF-R500 (5A) PTC fuse is rated to 30V and the MF-R1100 (11A) PTC fuse is rated to 16V. They will need to be replaced with real fuses.

Power Supply with diode If your board has a 1N4004 diode soldered in, do not apply more than 12 V to it. Original flavor Arduino Mega are rated to 12 V input. While Arduino Mega 2560 can take 20 V, it is not recommended.

  • $\begingroup$ i am using ramps 1.4 with polulo red stepper driver and arduino mega r3.i am using 2 nema 17 stepper motor only and not using any hotbed or somthig but stepper motors for x and y axis.i am feeding 11.9 volt supply to ramps.when powered on,can i plug the usb to computer? $\endgroup$ Apr 6, 2018 at 10:43
  • $\begingroup$ yes you can connect usb from arduino to pc. $\endgroup$
    – profesor79
    Apr 6, 2018 at 11:33
  • 1
    $\begingroup$ @sandeepkumar If you want to connect motors or switch wiring while the arduino is on and powered with any external DC source you can damage your arduino and also pololu drivers. $\endgroup$ Apr 6, 2018 at 17:41
  • $\begingroup$ @FernandoBaltazar very good hint! $\endgroup$
    – profesor79
    Apr 6, 2018 at 18:28
  • $\begingroup$ suppose i have connected 2 motors on ramps x and y,and external power supply is on,then can i connect my arduino to pc using usb,will it burn my board or not? $\endgroup$ Apr 8, 2018 at 15:46

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