arduino uno external power supply

Question

I have an arduino uno which is powered by batteries. I have 6 AA-Batteries (1,5V each) connected to Vin and GND.

Thats cool because I don't have any cables and works pretty good. The reason I need 6 AA batteries is, that I have a SIM900-module connected to my arduino uno. My USB Port (5V and 500mA) and my standard external power supply (9V and 1A) doesn't deliver enough current for the SIM900. But with the batteries the SIM900 gets enough power (current).

But there is the problem, that the batteries get sucked empty pretty fast and i don't want to exchange them every day. :-)

I searched for an power supply which can deliver 3A with 9V and found one. But i'm not sure if the arduino uno can handle that input via the on-board power-jack? The reason I want a 3A power supply is, that some users on the internet say that the sim900 sometimes uses more than the maximum current written in the documentation (which is 2A).

I'm an electronic noob.

So is there a risk if I try to use the 9V-3A power supply? Does the arduino only pull the power it needs? So when it needs only 900mA, it only takes 900mA even if the power supply can deliver 3A? As far as I know, it should work, because the batteries deliver as much current as the arduino (ad sim900) needs. So the batteries don't have an ampere limit, right?

Answer 1

The Arduino itself has a limit of about 800mA. That is imposed by the voltage regulator that converts the incoming voltage to 5V.

If you need more than 800mA then you need to provide your own regulated 5V power source and feed it in to the 5V pin (not VIN).

Suitable power sources are mobile phone chargers (modern USB ones). They generally come in multiples of amps.

And to answer your theory question - the current is the maximum that the supply can provide. It's the voltage that is fixed and the current varies depending on the load.