# Max Input current on Arduino Mega

Hello Guys,

I've search the forum here, but didn't found clear answer yet.

I have got an external power supply for which provides 12V and 1.5A output.

The question is if the Arduino Mega 2560 possibly could be damaged because of quiet big output current - max 1.5A?

FYI, I've got Arduino Leonardo and probably it was damaged because of that external power supply. Question 2 - didn't arduino leaonardo have max input current about 1A?

And finally third question, Would it be possible to safetly plug external power supply (12v, 1.5a output) and in the same time have the arduino mega plugged to USB?

I know there is automatic choice of power supply and so on, however before I potentially could damage that I would apperciate your help.

First question: No it will be fine, the 1.5A just means the power supply is able to output that much current. If you don't have a short it won't do that.

Third question: I tested that yesterday with my Mega2560 and it works.

Question 2 - didn't arduino leaonardo have max input current about 1A?

No it didn't.

How do you think you can power a 40W light bulb off a mains supply capable of supplying 30 Amps?

[url=https://en.wikipedia.org/wiki/Ohm%27s_law[/quote]**[u]Ohm's Law[/u]**[/url] describes the relationship between voltage, resistance, and current. Ohm's Law is the 1st thing you learn when you take an electronics class.

Simplified - More voltage = more current More resistance = less current

Now... We don't necessarily know the resistance of the Mega (and it's not a constant value) but we do know that the actual current depends on the effective resistance of whatever is connected to the power supply. (If we know the voltage & current, we can calculate the resistance, under the current conditions, by using Ohm's Law.)

The current rating on a power supply is the maximum current you can get from it safely and reliably.

I can connect an LED & resistor to a little 12V power supply and run the LED at 20mA. If I connect that LED/resistor to a 12V car battery rated for 500 Amps, the LED will still draw 20mA.

If there's nothing connected to the power supply no current flows! (But the voltage is still present.) If there's nothing plugged into your wall outlet, no current flows. If you plug-in too much stuff excess current flows, you blow a circuit breaker and the voltage goes to zero. i