Which is the maximum current Arduino UNO can endure from USB power?

Hello. I know powering Arduino UNO via USB must be done by a regulated 5V supply. But I haven't found any information about which is the maximum current allowed by this kind of supply. My question is caused by the convenience of using this power supply: http://www.adafruit.com/products/1994 (5V/2A) Thanks a lot!!

The 5A/2A CAN supply a maximum of 2A. It can’t “force” more than what the attached load wants to draw.

Hi.

As stated many times before, current is drawn from a supply, not forced into it. If your power supply is able to supply 2 Amperes, it does so if required. Your Arduino isn't capable to draw anything close to 2 Amps, so if it does, it has died already.

If you want to protect your Arduino from dying this horrible death, use either an advanced current limiter, or a simple, rudimentary current limiter by connecting it through a fuse.

The USB supply to the Arduino is protected by a “Polyfuse” as I described here, which is rated at 550 mA. This means that at currents above this, the Polyfuse will eventually open, and how long it takes to do so is inversely proportional to the degree to which you exceed this current limit (as it is a thermal fuse).

It will reset after some time (minutes, possibly an hour or so) after you switch off the supply.

Ok. Maybe I didn't explain myself very well (English is not my native language), sorry. What I wanted to know it's the last response:550mA. But...so...then, this power supply (http://www.adafruit.com/products/501 , 5V/1A) isn't suitable, neither?? Thanks a lot to all for your patience.

But take care, at 550 mA, you've got an important voltage drop and your board isn't operating at 5V anymore!

Osqui: Ok. Maybe I didn't explain myself very well (English is not my native language), sorry. What I wanted to know it's the last response:550mA. But...so...then, this power supply (http://www.adafruit.com/products/501 , 5V/1A) isn't suitable, neither??

A power supply is ABLE TO supply the amount of current it's rated to. If your supply CAN supply 1A but the board CAN only take 0.5A then your supply is fine since it can supply MORE than what you need.

Sacha22: A power supply is ABLE TO supply the amount of current it's rated to. If your supply CAN supply 1A but the board CAN only take 0.5A then your supply is fine since it can supply MORE than what you need.

Ook, thanks! Now I understand!! I've also seen this clear explanation in http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html (for all who needed)

"Every power supply has a rating it describes how much voltage it will give out and how much current IT IS CAPABLE of giving. So don’t think because it says it will supply 3 Amps it will always supply 3 Amps. It will only supply that much if it has a load with a low enough resistance. If the load has an even lower resistance it will want to take more current than the power supply can give, we say it is OVER LOADED. Therefore if your system takes only 1 Amp then you can use any supply that provides anything greater than 1 Amp."

That’s it. These are called voltage supply because they supply a fixed voltage.
If it says 5V supply then under normal operation conditions, the voltage will remain 5V whatever the current is.

In few words : the voltage is constant and the current is determined by the load.

Sacha22: If it says 5V supply then under normal operation conditions, the voltage will remain 5V whatever the current is.

In few words : the voltage is constant and the current is determined by the load.

Only if the supply is regulated - as this one most certainly is.

Unregulated supplies produce wildly excessive voltage when loaded to less than their full nominal capacity.

Thanks a lot. An interesting summary about current limit supported by Arduino UNO is explained here: http://electricrcaircraftguy.blogspot.com.es/2014/02/arduino-power-current-and-voltage.html

Paul__B:
Only if the supply is regulated - as this one most certainly is.

Unregulated supplies produce wildly excessive voltage when loaded to less than their full nominal capacity.

True, thx for adding that :smiley: