USB cable gets hot when plugged into PC and steppers fail

Hey guys, I’ve been working the last 3 days fixing my 3D Printer (cartesian DIY Kit with GT2560 Rev A+) because I plugged the Printer via USB into my PC wich caused some sort of ground loop or different voltage potentials at the 5V rail to let an rather high current flow through the USB cable, making it uncomfortably hot to hold in your hands. I didn’t notice this fast so it was plugged in like 10 minutes which apparently as enough to fry the CH340 USB to serial converter and all the stepper drivers (diddnd harm my PC though). I’m wondering how the steppers could get damaged by this, since they take the 5V, be it 4.8V or 5.1V, for their logic and this is still in their specifications.

Can someone explain why this happened in the first place, and why the steppers got fried?

... with some switching PSU's the "GND"-potential could be up to some ten to hundred volts different, if grounded and connected together or to other PSU's!!

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Quote
VDX
... with some switching PSU's the "GND"-potential could be up to some ten to hundred volts different, if grounded and connected together or to other PSU's!!

Thank You Victor;

I had the same thing happen to my 3D Printer.

Only when I plugged the 3D Printer into the USB port my Computer would short and reboot, I believe this was caused this voltage difference.
Luckily I only lost the 3.5inch Card Reader to this voltage difference shorting in the process, an it was easy an cheap repair job...

I solved my Problem by Adding a Raspberry Pi running OctoPrint to the Equation, I still control the 3D Printers with my Computer.
Although now I control them over a wired network. Could have chosen WI-Fi because of my local WI-Fi traffic, decide to go with a wired gigabit network.

You could use all the fancy features of OctoPrint.

Most used features from OcotPrint.
Ability to send sliced models to Octoprint, and Receive Streaming Web Cam Video as to monitor the 3D Printers.
Emergency Stop Button
Pre-Heat Options
Terminal Control Feature

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Computer Programmer / Electronics Technician

Thanks Viktor for the explanation, I guess I will have to change the power supply of the printer.
That would explain why the steppers died.

I did manage to change the CH340 to a new one I salvaged from a NodeMCU but was unable to get it working.

Would some diodes fix this problem if they are connected right behind the USB GND and VCC?
Don’t want to fry any more GT2560 Boards...

... depends on the inner "design" of the GND-leveling vs. line potential - in the worst scenario you'll get something like 120 Volts difference when connected, what's too much for most filters.

Had a PSU with 48Volts DC and "only" 3-5 Volts difference between this GND and the GND of my old notebooks, what killed the USB-port by melting some of the GND tracks!

With some comercial stepper drivers the vendor explicitely prohibits programming them with notebooks, for potential voltage differences of up to 120 Volts -- what shure will kill the notebook or the driver!!

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

You may find [duet3d.dozuki.com] helpful. Although it's written for Duets, it applies to all electronics except RAMBo and its derivatives.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].