Use of cable with laptop connected to mains

   #1  

mr_mortar

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Hi all,
I read on another source that one should avoid using VCDS on a laptop connected to the mains as this can cause some ‘ground loop’ issue.
My laptop has a good battery so haven’t had a need to connect to the mains yet. I seem to recollect using my previous VCDS cable with mains and never had any issues so hoping this comment I read is unfounded.


Thanks
 
   #2  

Quintus Rotam

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Hi all,
I read on another source that one should avoid using VCDS on a laptop connected to the mains as this can cause some ‘ground loop’ issue.
My laptop has a good battery so haven’t had a need to connect to the mains yet. I seem to recollect using my previous VCDS cable with mains and never had any issues so hoping this comment I read is unfounded.


Thanks

While you wait for RT to give a definitive answer, here's what I found:

VCDS requires a computer running Microsoft Windows (the HEX-NET can be used with VCDS-Mobile on other platforms but that use is still in beta testing). A Laptop is most convenient but a desktop PC can also be used.
We recommend a PC running Windows 7, 8.1, or 10 with at least 2GB of RAM (single-core Atom�-class processors are no longer recommended and devices with ARM CPUs are NOT SUPPORTED). Screen resolution of at least 800x600 is recommended.
If you are using a power supply for a laptop, it should be one specifically designed for that purpose, NOT a "universal" adapter.
Systems running Windows in a virtualized environment (for example Virtual PC on a Mac) are not supported. See also Question 1.8.​
If desktop PCs are ok to use, I would assume mains-connected laptops would be too (or there would be clear warnings set forth).
 
   #3  

Uwe

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A computer connected to the mains should never be a problem, no matter how crappy the mains power supply is -- provided you don't also have a battery charger connected to the car's battery and the mains at the same time.

If the car's ground is "floating", you won't get a ground loop, which is what causes problems.

However if you're using a mains-connected computer and a mains-connected battery charger at the same time, then the possibility exists, if both are poorly designed, that car's ground and the computer's ground will be at different potentials, and this can cause destructive currents to flow when you connect the two via a diagnostic cable. This is really quite rare because both the charger and the computer power supply have to be poorly designed. If either one is properly isolated, there won't be a ground-loop.

A far more common cause of ground-loops is a poortly designed 12V supply for a laptop tries to power the laptop from the car. In that case, only one thing has to be poorly designed. Here is an admittedly dated page warning of this problem. The bottom of the page has some tips on how to test for the problem non-destructively. Those tests would be equally applicable if you were using a main-connected PC and a mains-connected battery charger.

And lastly, if anyone is a real worry-wart, they could use a USB Optical Isolator.

-Uwe-
 
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