I have a Chinese Arduino nano clone, but I don't know if it's possible to connect the Arduino to external (5v) power and have a USB serial connection ongoing. I'm trying to make a PC controlled LED Strip that can also work on its own.

For example: the PC controls the Arduino sets it to a specific mode and I turn off the PC, but the Arduino should still be running even when the PC is turned off.

I'm new to the world of arduinos.

I'm planning to use this to control addressable LED RGB Strips and am planning to use a 4000mA max power supply.

  • Why don't you try to connect it and see for yourself? Commented Sep 12, 2016 at 10:14
  • i am afraid that i will fry my pc or arduino Commented Sep 12, 2016 at 11:00
  • Then you might want to buy genuine parts, or at least parts with a schematic you could analyse for such risks. Commented Sep 12, 2016 at 11:06
  • 5
    @DmitryGrigoryev "Arduino" is an open source hardware and software system. Ones made by other than holders of the now several trademartks are just as genuine as "originals" if they implement the core features. Use of the term "genuine parts" in this manner is against the spririt which the whole concept of "open source" seeks to promote. Commented Sep 12, 2016 at 11:54

4 Answers 4


Having used counterless Arduinos and clones, I can tell you that you can connect both without worrying about any danger. Unless you have a very faulty board, your pc won't be damaged, almost surely neither will the board, as is should select the most powerful source, between your usb or a battery/external PS, while leaving untouched the serial line.

  • 1
    this is the answer i needed thank you very much, but just to be sure have you ever fried something that way? Commented Sep 13, 2016 at 7:28
  • 1
    @TheKayneGame never
    – sassoPera
    Commented Sep 13, 2016 at 8:47
  • If you have solved your problem, please choose one of the answers; so that anyone with a similar problem can read it too
    – sassoPera
    Commented Sep 15, 2016 at 9:23

If you are new to something, you should start with reading manual.

Here's what official Wiki page of arduino nano says: https://www.arduino.cc/en/Main/ArduinoBoardNano


The Arduino Nano can be powered via the Mini-B USB connection, 6-20V unregulated external power supply (pin 30), or 5V regulated external power supply (pin 27). The power source is automatically selected to the highest voltage source.

  • So to be sure i won't fry my arduino or my pc when connecting 5v to pin 27 and connect the arduino to my pc at the same time? Commented Sep 12, 2016 at 10:58
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    For a genuine Arduino Nano you would be fine. For a cheap clone who knows, it depends if they skipped some parts to save money.
    – Andrew
    Commented Sep 12, 2016 at 11:01
  • 2
    Make sure you external power is regulated and connected to the same AC source as you pc. Should be perfectly fine then. Also refer to this thread for additional points regarding safety: arduino.stackexchange.com/questions/11885/…
    – tokky
    Commented Sep 12, 2016 at 11:11

The info about 100/150mA USB capability in PC is incorrect. Any normal (not "low-power embedded") USB host must supply 500mA (for USB2.0 ports) and 900mA for USB3.0 ports. In a typical PC this power comes from standby +5VSB rail from system Power Supply. Power rating for this rail is no less than 2A for AT12 compliant PC. Of course it is not advisable to take all this power from one port, due to contact rating limits, and possible polyswitch overcurrent protection of USB ports.

Therefore, if the attached USB device draws total less than 1-1.5A, the design should work fine even if PC is in standby mode (turned off but still connected to AC outlet).

However it is still preferable to use a stand-alone power for this kind of projects. The Arduino board must be designed in a way that, if connected to external higher-voltage source, it would not backdrive any significant current into USB VBUS pin. Usually it gets accomplished by means of one single Schottky diode between VBUS and internal power rail on Arduino board.

You can check if your Arduino drives anything back: power the Arduino with, say, 12V power supply, and check with a Multimeter if VBUS pin on the (unattached) USB connector has any voltage. You should load the VBUS with 10k-15k resistor, and the voltage should be small, 200mV or less, if I remember correctly.

ADDENDUM1: Just checked with Arduino-nano schematics. Yes, there is a "auto selecting" Schottky diode, so there will be no backvoltage on VBUS. However, the Arduino design violates another USB requirement - no signal on any connector pin when VBUS is inactive (low). In the Arduino-nano the VBUS does not control the state of FT232 bridge, so it will always pull-up D+ (USBDP) line as soon as 5V is applied, which is in violation of specs. The side effect of this back-driving is that your PC might not re-connect with the Arduino after waking-up, although it is a rare case these days.


You can connect the Arduino nano to recommended external power supply i.e 5V when it acts as a standalone device with other circuitry. As it is connected to PC it starts drawing power from PC(as PC is acting as a host here) and at the same time serial communication goes on. Now if you want to simultaneously connect the nano to PC or any other host say tablet and external power supply it is recommended that you go for an OTG cable cum power splitter y-cable.

But do not rely on power from PC if you have many sensors or components interfaced to aduino nano as PC is capable of giving max current 100mA in USB 2.0 and approx 150mA in USB 3.0

  • I was not planning to use PC power alone, and the current draw will be around 3 to 4 Ampère. Commented Sep 12, 2016 at 18:22

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