Connect printer to PC

Ok so... I'm really quite embarassed to even open this post and ask... but my googling skills have held no result on the matter...
I want to SAFELY connect my Prusa i3 with Ramps 1.4 to my PC, without any shorts, smoke and such things. I know that the PSU powers the ramps, and that (through experience) if you then connect the USB cable to the PC everything will blow up...
The only thing I could find is this: [asensar.com]
that seems to suggest that reversing the order of operation makes the difference.
Problem is: I'm too afraid to try, and would like someone to point me towards the solution (if this doesn't work) without messing the whole thing up once again.
P.s: do you think it will be a problem to have the same board that "blew up" when connected to the PC last time? I'm asking because everything works fine and I haven't substituted it yet...

... seems, your ground potentials of the PC and PSU are different - so high currents flows either trough the GND connection or even through the +12V connection and cause chaos.

Better search a better PSU with proper defined GND potential ...

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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]

So I assume I'm not safe powering everything up, as current will still flow wrong ways...?
The whole point for connecting it to PC was that I need to run PID autotune and check the values. Is there another way that doesn't require the PC?

Actually... what would happen if I took an USB cable and cut off the 5v and/or GND wires? Would that be a viable solution? Or would it interfere with the USB protocol in some ways I can't even imagine?

... you need a good/equal GND potential for the USB communication and it's wired across most electrical connections and plugs too, so cutting the GND wires won't help.

If the potential difference is only capacitive, connecting the different GND's with a thick wire before plugging and switching the electronics will help.

But sometimes it's much more, so currents of some Amperes can flow through the USB cables GND wire and shield - I had two occasions, where the USB cable get too hot to touch!

So better search a good pairing ...

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

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

What is Blow up? Explosive detonation -- and shrapnel,
Star-Trek like arcs. sparks and zaps
or just letting the magic smoke out

What gets warm/hot before blowing up? Wear your bomb suit and welding goggles?
What is melted, welded, or blown up on board? Show photos

A Ramps 1.4 setup is a arduino mega 2560 with a RAMPS expansion card installed on top
Unless you do some special things --- arduino is powered by the USB connection.
If you are using a USB hub --- it should be a powered hub.
Motors and heaters powered by 12/24v external supply

Are drivers (polulus) installed correctly, jumper under them installed correctly?

Probably wired wrong --don't diddle with it with it ON -- you will fry the drivers
you are shorting out something

take RAMPS off
load some test code to arduino ---- blink does the LED blink?

See
[reprap.org]
Check out wiring and supplied voltages and make sure +. - is correct

Re-install RAMPS card

You could load up test code
[reprap.org]
that will turn on heaters and move motors
then load up properly configured Marlin or Repetire
then your set

If you are "too afraid to try" you should NOT be building s 3D printer

To avoid damage when you hook up a 3D printer controller to a PC via USB, you need a good connection between the negative power input terminal of the electronics and the negative power output terminal of the PC. Otherwise the system will try to to complete the circuit through the ground wire of the USB cable. When you turn on the bed heater in particular, this is likely to cause damage.

Power both the PC and the printer PSU from the same mains power distribution block, to avoid ground noise problems.

Another option is to connect a laptop that is running from its battery only, then you don't get a ground loop.

Using Ethernet or WiFi instead to connect the PC to the printer avoids USB ground loop issues, but this isn't available on budget electronics. Some LCD control panels allow you to enter and send any gcode command, but again they are not yet supported by budget electronics.

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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].

Thanks for the replies! After posting the message last night, I started messing with the firmware to see if I could in some way implement a .txt log output for the values found after running the test. Long story short, I found out that adding "U1" at the end of the M303 command on Marlin, the board will save the Kp, Ki, Kd values and you can then find them just by using the printer alone. So this is what I did. Since I was getting some "Thermal runaway" error and I had just purchased the new hotend, I had thought it would be enough just to tune the PID for the extruder. It wasn't. I managed to get everything working in the end by having the fans gradually power up with layers (so no full blast at second layer).

Anyway, I might try to connect the printer to the PC even though I don't need to do it anymore. You say that using a laptop will not make the magic smoke again?

I think I haven't explained myself well enough: I'm now able to print. Everything on the RAMPS and the Arduino works perfectly, except the USB connection. The fried component is on the Mega, and is placed (when looking at the board from above, keeping the USB exit on the top right) to the right of the USB connector. Still have to figure out what that is. If you think you could help me identify it, I can post pictures later in the day (when home).

Again, thanks for the help and the support!