I want to use an Arduino Yún as a kind of outdoor weather station. I want to supply the power for the Yún with a 5V USB-Charger. Using a normal USB cable everything works fine. But as the weather station shall be far from the next power socket, I made the USB cable about 10 meters longer. Now the Yún does not power up any more.

Has anybody an idea why?

Should I use a 12 V power supply and a 7805 power converter instead?

  • Dmitry's answer is generally correct but I disagree with the notion that “voltage drop” is the problem, unless you used extremely thin wire in the extension. You don't say how you made the USB cable longer. If your experience with building cables is limited, it's more likely that one or more of the connections is open or wrong than that too much voltage drop is occurring. – James Waldby - jwpat7 Jan 8 '16 at 23:06
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    After failing with a rather thin cable (a former telephone cable soldered into a normal USB cable) I tried a much thicker cable, but the Yun would not start either. As I think I am rather experienced with soldering, I do not think the connections are the problem. Does it make sense to measure the resistance of the cable? So I will try the power converter solution within the next days. – bhneuner Jan 10 '16 at 10:45

The USB specification limits the length of a cable between two devices to 5 meters. When you make a longer cable, you're going out of spec, which means it is not guaranteed to work anymore.

Since you're only supplying power, the issue is (as you have guessed) the voltage drop in the cable. However, the voltage drop will depend on how much current Arduino is consuming at any given moment. Supplying it with a higher voltage without a converter is dangerous, because it will lead to overvoltage you won't be able to control.

I'd suggest trying better cables first: thicker and stiffer cables have thicker wires, and may have less voltage drop. You can also make your own cable (provided you can solder) using only two thick wires for power.

The ultimate solution, like you said yourself, is to deliver higher voltage over the wire (12V would do) and install a power converted (12V to 5V) near your Arduino. That way, the voltage drop in 5V line will be small, and the voltage drop in 10m 12V line will be compensated by the converter. Actually, the intermediate voltage may be higher: you can simply drop a mains line (220V or whatever you have) to your weather station and place the same USB charger near the Arduino.

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    It works now. I replaced a 12 V power supply and added a 12V / 5V DC converter just before the Arduino Yun. The first try with a change of the cables with a higher diameter had no effect. – bhneuner Jan 17 '16 at 22:44
  • @bhneuner I'm glad it worked out, and thanks for taking time to report back! – Dmitry Grigoryev Jan 18 '16 at 10:11

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