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Stray Voltage can damage your 3D Printer

AETEKAETEK Posts: 106๐ŸŒŸ Super Member ๐ŸŒŸ
edited July 2018 in Modifications & Upgrades

JGAurora A5 & A3S USB Printing - Important Information

Quote from Youtube Userย  Rick Fedorowicz:
"Interesting. At one point, while attempting a firmware update, I had some components near the USB connector on the main board burn up. I smelled smoke and pulled out all the cords and power. I replaced the board and the USB jumper lead from the board to the chassis port and the blue USB cord, suspecting a problem with the cords and possibly a potential on the chassis. I did not check any further but I Have not had a problem since."

Quote from Wikipedia:
"Stray voltage is any case of undesirable elevated electrical potential, but more precise terminology gives an indication of the source of the voltage. Neutral to earth voltage (NEV) specifically refers to a difference in potential between a locally grounded object and the grounded return conductor, or neutral, of an electrical system. The neutral is theoretically at 0ย V potential, as any grounded object, but current flows on the neutral back to the source, somewhat elevating the neutral voltage. NEV is the product of current flowing on the neutral and the finite, non-zero impedance of the neutral conductor between a given point and its source, often a distant substation. NEV differs from accidentally energized objects because it is an unavoidable result of normal system operation, not an accident or a fault in materials or design."

the problem is not a poor shielding, which could lead to data loss, but unwanted external voltage that can occur between the computer and 3D printer. The problem occurs more often because of direct grounding with PCs than with notebooks.
I think the "solution" with the new USB cable does not make sense.
The "new" USB cable will have at least one end no connection to the outer shield to avoid ground fault currents.
If you forget this and use a standard USB cable, the danger is immediately present again.
That's why I came up with a different solution.
The goal is to mount the power supply in isolation. This allows the power supply to remain grounded, but it can not feed external power to the computer via ground. For this purpose, I have printed 4 PLA mounting blocks that connect the power supply mechanically but not electrically to the printer housing. Then the problem with the unwanted external voltage will no longer occur.

After the installation, I took a measurement. The computer and the A5 were connected to a multiple mains socket. I could still measure 7 volts AC. Then I measured the short circuit current. Due to the high insulation resistance, however, I could not detect a measurable current flow. The voltage is the prerequisite that current can flow. However, if the resistance to be overcome is large, then only a very tiny current can flow. This current was so small that I could not measure it. Such small currents also do not cause any damage to the hardware.

Post edited by AETEK on


  • Samuel PinchesSamuel Pinches Posts: 2,997Administrator
    edited June 2018
    I think for metal chassis devices, the metal chassis should definitely be grounded. In case a live wire is damaged or comes loose and makes the case live, then your GFCI will cut power automatically. If power is flowing through the board backwards from the USB then perhaps a USB isolator is a better option:ย https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com.au%2Fulk%2Fitm%2F282630553997

    most USB devices are better designed. The MKS products are all designed to be dirt cheap, but have very few board protections, which makes them very vulnerable to damage from this kind of thing.
    Post edited by Samuel Pinches on
  • AETEKAETEK Posts: 106๐ŸŒŸ Super Member ๐ŸŒŸ
    edited July 2018
    In a German review of the A5, the author has measured the connection of the ground between the power supply and the printer's metal case. He found out that the black paint is sometimes so thick that it acts like an insulator and the printer housing is not grounded. In other cases, however, the grounding may be connected if the paint is damaged / thin. That may be the reason why some users have problems with it and others do not.

    Every solution has its advantages and disadvantages. That's why I designed the isolators very stable. The power supply itself remains grounded. To prevent the live wire from coming loose and getting in contact with the printer metal housing, there are mechanical precautions (e.g., securing with cable ties).

    I do not think that the MKS products are badly secured. The mainboard is used universally. Other motherboards for 3D printers also have no USB isolation, as far as I know. It depends on how the 3D printer is supplied with power. My old Velleman K8200 3D printer had an external power supply (like the notebook) with a plastic case. This power supply did not need grounding because the case can not conduct electricity (is isolated). The printer is made of metal, without grounding. I never had any problems with it. Now I have replaced the Velleman's power supply with a more powerful one. You can either place the power supply externally in its own plastic case or mount it isolated from the printer's metal chassis.
    For me, this is the best solution because I do not have to think about it when I connect 3D printers and PC / notebooks. The problem is that if you notice (it smokes), then a device is already broken. No matter which device it gets (3D printer or computer) it is very annoying. Which solution one prefers can decide each oneself.
    I prefer simple solutions.
    Set it and forget it.

    Post edited by AETEK on
  • Samuel PinchesSamuel Pinches Posts: 2,997Administrator
    For the A3S with the external power supply I would not be worried, but for the A5 I would still prefer to improve the quality of the grounding, rather than remove it. I'm no electrician, just need to play it safe with mains voltages.
    Take care, and good luck.
  • AETEKAETEK Posts: 106๐ŸŒŸ Super Member ๐ŸŒŸ
    I have a profession radio and television technician and the technical school for electrical engineering.
    You make, from a technical point of view, from the internal power supply an external.
    Of course you have to prevent the power supply from breaking loose mechanically.
    But even if this happens, the case of the power supply is still grounded. If there is voltage on the outside of the power supply housing due to a defect in the power supply, then the fuse will fly out immediately.
  • grzerygrzery Posts: 1Member

    My experience teaches that this printer (A5) in the field of overvoltage protections is poorly designed!

    I felt the roast of electronics when I put the pendrive into the USB port of the printer. In my opinion, there was a short-circuit of the ungrounded housing (how did the printer get the CE mark?). High voltage between the casing and the "mass" of the pendrive damaged the entire electronics of the printer.


    For those who still have functional devices, I recommend re-engineering the USB ports (both) so that the pedrive can not connect the printer's case and electronics ground.

    It is not excluded (let live modesty) that other similar failures of these printers had exactly the same reason as in my case. The short-circuiting element was not a pendrive in this case. It was a USB cable plug.

    The problem of the occurrence of damaging potentials between device interfaces has been known for a long time.

    He appeared, among others, in the case of connecting the computer and the printer with the Centronics interface. It was known that connecting the printer's interface (cable) to the computer had to be done only with the printer turned off (and even better with the power cable removed).

    It was always necessary to ensure that the computer and the printer were powered from the same power strip with a very good grounding.

    I have just bought a new motherboard and display. I plan that when I receive the package, first of all, I will connect all the metal elements of the printer's case with a thick cable.

    The cable will also be connected to the power supply ground. I will also apply a modification to prevent short circuits when inserting something into USB ports (just in case).

    In the case of printing from a computer, I will take care that the computer is powered from the same good power strip. I remind you that IMHO first connect the USB cable and then turn on the printer.

    The use of the separator suggested by Samuel Pinches also does not seem to be wrong.

    Because in Poland the standards do not specify which cable of the power cable is high and which low application of the two-wire circuit breaker does not seem to be an error (now it is a single-wire system).

    That's all. I apologize for my "Google English".

  • Samuel PinchesSamuel Pinches Posts: 2,997Administrator
    edited July 2018
    @grzery ย I'm sorry to hear of more people having bad experiences with electrical faults on theย A5ย  Thanks for sharing your experience, and your recommendations. I hope you can be up and running again soon.
    Post edited by Samuel Pinches on
  • sanjibukaisanjibukai Posts: 34๐ŸŒŸ Super Member ๐ŸŒŸ
    Hello, I didn't notice that "drawback" but it definitely needs to be fixed (or at least considered)...
    Apart from adding plastic washers (as AETEK) how someone can improve the grounding?
    Is it possible to scrap the paint of the case somewhere and connect the ground?
  • AETEKAETEK Posts: 106๐ŸŒŸ Super Member ๐ŸŒŸ
    So you make the problem worse. :(
    An alternative is a isolating transformer with galvanic isolation of primary and secondary circuits.

    Note: The output has no ground connection:

  • sanjibukaisanjibukai Posts: 34๐ŸŒŸ Super Member ๐ŸŒŸ
    edited July 2018
    ย :* I know one can go really high in best of the best equipment...
    But I mean not every 3d printer needs this..

    Here, I understood that the grounding is not good because of the paint, right?

    Or maybe there are two things:
    • The grounding itself (which is recommended for metal chassis device as stated by @Samuel Pinches
    • The current leak in the USB..
    It seems that, actually, the A5 has "proper" grounding, right? I mean the metal chassis is grounded, right?
    But there is a problem with the USB..

    Using the black cable, solve (in a bit hacky way) the second problem.
    So using the plastic washers... But in that case, the grounding will not exist anymore, right?
    Post edited by sanjibukai on
  • AETEKAETEK Posts: 106๐ŸŒŸ Super Member ๐ŸŒŸ
    the black color effect like my insulator blocks.
    But you can not rely on that. Therefore use the Insulator Blocks.
    The problem is:
    Under certain conditions, electrical power can flow between the ground line and data lines. This can then lead to defects. It is nothing to do with the A5 printer, but can always be a problem when connected to grounded devices. My power supply is grounded, but not the black A5 housing. But I have already explained everything above. It is clear to me that this is not easy for the average user to understand.

    I had defects through this problem years ago. At that time it was an Atari Falcon computer (grounded) and an external HDD drive in the metal housing (grounded).
    At that time, the data transfer chip (SCSI) was destroyed in the computer. The repair was very expensive. After using an isolation transformer, there were no more problems. Due to the galvanic isolation, the connection to earth becomes unnecessary and thus no current can flow in this way.

    For safety reasons, the earth should remain connected to the power supply on the A5.
    If one were to touch the A5 power supply housing with the computer USB plug, then damage could result.
    But this case is very unlikely when the A5 case is closed.

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