I have USB charger battery pack with two output ports (Fremo C510). One is marked as 5 volts 1 amp, and the other as 5 volts 2 amps.

I'm building a toy robot and would like to run the UNO off of one of those ports, and the motors off of the other.

Can I safely do that? I have two main concerns:

  • Can I safely power the arduino with that current?
  • If I power both the motors and the arduino from that source (two usb ports connected to the same battery), will I still have to worry about spikes from switching the motors on and off? I don't know how those ports are wired to the actual battery inside.
  • I don't know how those ports are wired to the actual battery inside. -- Neither do we.
    – Majenko
    Feb 16, 2017 at 16:30

1 Answer 1


You can power the Arduino from either side, since it will only draw what it needs, and most arduinos are powered from a .5 amp USB port. But you'll want to reserve the higher current side for the motors.

Make sure your motors' total draw (including starting current) doesn't exceed the 2 amps available.

Unless you can find out for sure that the two power ports are isolated from one another, you're better off to assume they are not and provide motor spike damping yourself.

  • Sometimes the small-print in these chargers says that they can supply a max of 2.1A in total - you might want to check that.
    – Mark Smith
    Feb 16, 2017 at 17:18
  • Even if that is the case with this charger, the Arduino very likely won't draw even half an amp, leaving well over 1 amp out of the of the total for the motors. They would require the 2 amp port to take full advantage of it. In that case the motors will have to use less than the full capacity by however much the Arduino needs to function.
    – JRobert
    Feb 17, 2017 at 18:07

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