I'm trying to identify the issue with my portable monitor. While testing it I noticed a weird (at least for me) thing that I can't understand.

I set voltage on my power supply to be exactly 7.2V. When I measure it on the power supply terminals it indeed shows 7.2V. Now when it's measured on the battery connector (where I inject the voltage) it measures only 6.8V.

Does it mean there is a voltage leak to the ground? I'd expect my power supply to show 6.8V on the screen but it shows 7.2V as set.

  • 3
    \$\begingroup\$ Wires all have resistance. If a current is flowing through them, there will be a voltage drop. Do you know the current and the wire gauge? \$\endgroup\$
    – Justin
    Oct 6, 2020 at 13:37
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    \$\begingroup\$ Voltage doesn't leak. Current does. \$\endgroup\$
    – Transistor
    Oct 6, 2020 at 13:44
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    \$\begingroup\$ You fail to mention what is very important: how much current is flowing? When a current is flowing, a voltage drop will occur across every resistance in the circuit where that current is flowing. Such resistances are always present in cables and in connectors. \$\endgroup\$ Oct 6, 2020 at 13:55
  • \$\begingroup\$ That's indeed a voltage drop across the cables (from V = I R), as others have pointed out. If you are using long and thin cables then the drop can be more significant if the current increases (e.g. you can see the same thing when you charge your smartphone with your wall charger: charger's output is 5.1V at the output jack but your phone's jack sees 4.6V). \$\endgroup\$ Oct 6, 2020 at 13:55
  • \$\begingroup\$ How much current battery is taking? @Maciej \$\endgroup\$
    – Deepak
    Oct 6, 2020 at 14:18

1 Answer 1


Do you measure the 7.2 V on the PS output while the battery is connected? There could be a significant voltage drop across the cables and connectors between your PS and the battery.

  • \$\begingroup\$ Thanks. This is indeed a voltage drop due to wires resistance. \$\endgroup\$ Oct 13, 2020 at 22:13

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