Arduino power via usb and external?

Forum 2005-2010 (read only) General Frequently-Asked Questions
1

Hi there,

I have a general question.
Is it possible to connect the Arduino board both on the usb-port and an external 12V powersupply at the same time? I need more current for an external motor and must have the usb-connection for sending data through usb.

Thanks in advance!

Erik

2

Yes, you can have it hooked up to both external power and USB power. If both are connected the board's auto voltage selector will use the external power rather then USB power. You may gain just a little more current however, as the limit is dependent on the value of voltage from the external power source. Too high a voltage causes higher heat dissipation in the on-board +5vdc regulator. 8 vdc is around the optimum external voltage to use, still I would not expect to be able to draw much more current then around 700ma or so when using the external power source. The USB has a 500ma limit.

Lefty

3

Its probably worth noting that if you're powered from an external supply and reattach the USB lead, or restart the PC, the Arduino will reset.

4

I suppose that you can always power your power-hungry peripherals with a separate power source (i.e. 5V) and let the Arduino be powered by USB. That is probably the better way.

5

Is it possible to connect the Arduino board both on the usb-port and an external 12V powersupply at the same time?

As has been explained, yes, but it might not be the best approach.

I need more current for an external motor and must have the usb-connection for sending data through usb.

Power the Arduino from USB.
There is no need to put the external power source into the Arduino power socket.

Use the external 12V power supply to power the motor.
Unless you isolate driving the motor control from the Arduino (e.g. using an optical coupler) connect the ground connection of the Arduino to the ground connection of the external power supply.

If you only need the motor to turn in one direction, there is no requirement for anything more than a transistor or power MOSFET (or even a relay) to switch power to the motor. Have a google for details of this set up.

HTH
GB