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What would happen if I connected a fan as shown in the following picture:

Fan connected to +12V of the power supply and GND of the arduino

  • +12V is supplied by the power supply that also powers the Arduino.
  • GND, however, is connected to a GND pin of the Arduino instead of the power supply.

I guess that would not work? Or are GND from the Arduino and GND from the power supply identical in this case?


If you read the accepted answer, please also note the comments below. The power consumption of the consumer (fan) is important.

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    why are you not connecting it to the power supply ground?
    – jsotola
    Nov 28 '20 at 21:36
  • The fan, together with other parts, is connected to the Arduino via a connector with a limited number of pins. GND from the Arduino is already connected there. I would save contacts if I could reuse this GND instead of also connecting GND of the power supply.
    – xoric
    Nov 28 '20 at 21:56
  • it is a good idea to avoid connecting external device grounds to the arduino ... the current that is drawn by the external device can create a voltage drop between the arduino ground and the power supply ground ... that would lower the voltage between the power pins at the arduino
    – jsotola
    Nov 28 '20 at 22:05
  • Thank you @jstola. Could I just connect all consumers (no matter if they are powered by +12V of the power supply or +5V of the Arduino) to GND of the power supply (and not use the GND pin of the Arduino at all)?
    – xoric
    Nov 28 '20 at 22:19
  • yes, you definitely could do that ... anything that has a motor or a solenoid and things like LED strips should be grounded at the power supply ... sensors would be ok to ground at the arduino, unless they draw many tens of mA
    – jsotola
    Nov 28 '20 at 22:30
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"Ground" is just a lump of metal and each ground "pin" is connected to it. That includes the ground connection in the barrel jack. It's all one thing.

Wherever you connect your fan's ground to it's all ground. That is, as long as all grounds external to the Arduino are connected, ultimately, to the Arudino.

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    To add to the above: Because wires and PCB traces are not perfect conductors, that is have resistance, there are practical differences between between different labeled "GND" points. So it does matter where your current is traveling within the network of conductors that are labeled "GND". High currents traveling on the ground must travel through GND conductors (traces, wires) capable of handling those currents.
    – timemage
    Nov 28 '20 at 21:44
  • Indeed, but given that the current limit of the headers is only 1A you won't be passing that much through the Arduino's ground pins...
    – Majenko
    Nov 28 '20 at 21:48
  • Thank you for your comments. The fan is actually very powerful (originally intended for cooling server PCs - it draws 1A). In this case, in consideration of your remarks, it would probably be better to connect GND of the fan directly to the power supply?
    – xoric
    Nov 28 '20 at 21:51
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    @xoric For that kind of current, yes, connect it to the power supply's ground for the lowest impedance and highest current handling.
    – Majenko
    Nov 28 '20 at 21:54
  • Thank you @Majenko, your explanation was very helpful.
    – xoric
    Nov 28 '20 at 21:59

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