At first I am sorry for my bad English.

I am making robot which can do a lot of things...

If I connect arduino on my robot with PC via USB, the robot works properly. If I use external power supply (9V battery) the robot is doing almost nothing.. The diodes are little bit blinking and sometimes dc motors make motion... And thats all. Batteries are charged. Where's the problem?

Everything I want is make into motion dc motors.. With 5V USB it works. With external power supply not (9V battery).

  • 2
    9V batteries are crap for anything that needs any real amount of current. Nov 17, 2014 at 0:41
  • Does it really show you 9V? If it is written on side it doesn't mean it's 9V
    – Martynas
    Nov 17, 2014 at 6:01
  • Yes, It really has 9V. I have 2 same 9V batteries. One for DC motors and one for arduino. DC motors are working properly with this battery but arduino is not.
    – Mr. Robot
    Nov 17, 2014 at 9:15
  • probably you were right. If I disconnect all sensors from arduino, the DC motors are making some motion... they're really slow but they are moving.
    – Mr. Robot
    Nov 17, 2014 at 9:33
  • what I should use instead this 9V battery?
    – Mr. Robot
    Nov 17, 2014 at 9:41

1 Answer 1


I got a fresh 9 V out of a packet and measured it.

 9.58 volts

Now with a load of 500 mA (which you quite likely would get with a robot) it dropped to:

 7.4 volts

With a load of 750 mA the voltage dropped to 6.6 V which is below what you are supposed to supply via the power jack.

And that was with a fresh battery, testing for a few seconds.

Those 9 V batteries are just not designed to drive motors.

I suggest a somewhat heavier-duty battery, like 5 x AA batteries, at least for the robot part.

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