Hello,
My question is quite simple but I haven't found the answer in the datasheet provided for the Arduino Mega, which is the max amperage supported in DC input ? For a project I need to feed the electronics with 1.4 ampere, will it damage the card if I plug-in a 9V / 1.5A (or 2A) adaptator in the Arduino Mega Board ?
Thanks for your answer,
Thomas
you dont feed current, your circuit draws it, whether you components can handle it or not
if your just plugging in 1.5 amp wall warts the mega + everything connected to it, will consume whatever it needs, nothing on the mega is designed to handle that much current, the avr chip plays by the same rules (40ma max on a pin, total package 250mA and even those are going to seriously strain it) and the voltage regulator is only good for a couple few hundred ma
so if your going to need a 1.4 amp draw, your going to need to come up with a pretty beefy way to drop 9 volts to 5 volts while being able to provide that current, and your going to have to buffer the outputs of the mega so whatever it is your doing doesn't source the current though the arduino (though IC's or transistors)
more information is needed
Thanks for your answer ! I was guessing that the Arduino board just take its 250mA to function correctly and the other amperes goes directly to my electronic composant (it's a thermal printer) and not damage the board.
So if I understood well, I need to give current to my thermal printer externaly by plugging it directly to my DC 9V adaptator and my Arduino to the USB ?
(To be totally honest, I don't understand very well because there's plenty of examples on the Internet where users plug directly their printer to the VIN and draw the amperes they need)
The seriese protection diode is only rated at 1A.
(To be totally honest, I don't understand very well because there's plenty of examples on the Internet where users plug directly their printer to the VIN and draw the amperes they need)
There is a lot of rubbish on the net.
Thanks for your confirmation. So in my case, I must keep in mind that the Arduino board can take 1A max!
Yes. 
Grumpy_Mike:
There is a lot of rubbish on the net.
Yeah, try YouTube.
Particularly when the comments start saying: "uh oh, I've wandered onto that part of YouTube".
LOL
I figured out that in fact I can use any amperage to power the whole thing, because my DC 9V 2A is plugged into a breadboard, my other components and my Arduino board takes the current from it so each circuit draw only the current it needs !
Taahl:
I figured out that in fact I can use any amperage to power the whole thing, because my DC 9V 2A is plugged into a breadboard, my other components and my Arduino board takes the current from it so each circuit draw only the current it needs !
Exactly. I am surprised by how many people are confused by this concept.
Yeah in fact it's not obvious when you are a beginner ! 
I wasn't sure that I could power my breadboard with my 9V DC 2A and plug both Arduino board and other components to the same alimentation because Arduino support only 1A but if it takes just 500mA there's no problem anymore, but it's tricky to understand ah ah.
So that means, I can connect the 4A adaptor to the rails on the bread board and connect the + back to VIN on the arduino and all is good then !