I would like to reach zero potential difference between me and my laptop (to avoid ESD) before opening the back cover.

I'll connect my wrist strap to a common ground point, thru a resistorized coil cord.

I'm considering to connect the ground of the DC-jack to the same point. Luckily, i have a spare power cable, which i can cut thru.

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  1. Is this a good plan?
  2. Is it a good idea to also connect V+ (from DC-jack, not from adapter) to the common ground point?

You are over-thinking this. If you want a handy ground reference to your laptop. you can clip onto the ground/shell of a USB or HDMI (etc.) cable plugged into the laptop. No need to sacrifice a perfectly good cable.

If you really want to make a dedicated cable, use some old USB cable or something easily replaceable.

In reality, as soon as you touch the screwdriver to the screws holding the laptop together, you have ipso-facto "grounded" yourself to the laptop.

  • 1
    \$\begingroup\$ Note that it's not a given that a USB connector shell, especially one at the far end of a cable, will actually have a conductive path to the device's ground. Perhaps it should but that doesn't mean that with any random piece of gear in someone's possession (especially the cable) that it will. \$\endgroup\$ – Chris Stratton Nov 22 '16 at 16:40
  • \$\begingroup\$ The USB spec says that the overall shield must be firmly bonded to the connector shells. But it is easy enough to test with a meter. \$\endgroup\$ – Richard Crowley Nov 22 '16 at 16:54
  • \$\begingroup\$ Yes, i already sacrified an old mouse to get myself an USB-cable. But then i thought the GND terminal of the DC-jack would be perfect, because internal GNDs lead to that point, right? \$\endgroup\$ – Marty Nov 22 '16 at 17:01
  • \$\begingroup\$ @RichardCrowley, should the connection between USB_GND and common ground point with or without a resistor in between? \$\endgroup\$ – Marty Nov 22 '16 at 17:02
  • \$\begingroup\$ All the grounds are connected together. For the purposes of static dissipation, they are identical. It is much less expensive to sacrifice a USB cable than a power cable, at least IME. \$\endgroup\$ – Richard Crowley Nov 22 '16 at 17:03

By grounding yourself you are preventing the introduction of an external source of power to your laptop (ESD). Grounding the DC jack will only discharge any residual power in the laptop which isn't necessary.

Make sure you have removed the laptop's battery before opening the back cover. This will prevent the risk of shocking yourself and shorting out components on the motherboard.

  • \$\begingroup\$ The goal: to be at the same potential as the internals on the inside of the laptop, in order to avoid ESD, which is caused by a potential difference. My guess would be that grounding the GND from the DC-jack to a common point ground, is in fact: bonding to the ground-plane of the laptop's motherboard. \$\endgroup\$ – Marty Nov 22 '16 at 14:32
  • \$\begingroup\$ Yes you would be setting the laptop at a common ground potential as yourself and therefore you will theoretically have zero potential difference. Connecting the positive DC terminal will be unnecessary but since the battery is removed and it is connected to no source, shorting it to ground should not harm anything. You can see this by measuring the voltage between the V- and V+ of the DC jack. I would avoid shorting things unnecessarily tho. \$\endgroup\$ – Steve771 Nov 22 '16 at 14:46
  • \$\begingroup\$ My thinking behind "connecting the positive DC terminal to the common ground point" is: when the laptop is at a lower potential than my body's potential, then it can be charged a little bit via a wire to the positive DC terminal, in order to reach my body's potential. So, my idea: 2 separate wires between DC-jack and common ground point. (V+ to that point and GND to that point.) But i'm still wondering if it's a good idea. \$\endgroup\$ – Marty Nov 22 '16 at 14:56
  • \$\begingroup\$ Note: the wrist strap keeps my body at earth potential. So, i could also say: when the laptop is at a lower potential than earth potential, then it can be charged a little bit via a separate wire to the positive DC terminal, in order to reach earth potential. At least, if it's a good idea to connect both V+ and GND (of the DC-jack) to a common ground point. I'm curious. \$\endgroup\$ – Marty Nov 22 '16 at 15:05
  • \$\begingroup\$ Yes but if the V+ has a closed circuit to the V- that you want to ground, any charge at the V+ will be made common to V- as there is no source supplying more potential to the V+. \$\endgroup\$ – Steve771 Nov 22 '16 at 15:09

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