problem with DC adapter

Hi everyone,

When I power my Arduino NG with an DC adapter many times the script does not start. The power led is ON but the program does not start running. I have to try many times until (usually) it works. That does not happens when powered through USB.

I've try the following adaptors and they all have the same problem: - 9V 1200mA 15W - 12V 1200mA 15W - 12V 2A ?W

Any idea of what can cause the problem? To many mA??

Thanks a lot in advance.



  • 12V 2A ?W

Wattage = Voltage x Amperage

12V 2A = 24W theoretically.

That doesn't particularly help with the problem, but just thought I'd clear that up.

To many mA??

No you can't have too many. It is the capacity of your supply, that is what it CAN supply not what it DOES supply.

As to your problem, have you tried pressing the reset button if it fails to start. It could be due to the rise time of your PSU.


Thanks everyone for the quick answers.... and the corrections ;-)

Mike, I do not know what you mean by "rise time of the PSU".


sometimes power supplies take a moment to get up to spec when you first kick it on, eventho its almost instant to us, its an eternity for a cpu

That's right. You still haven't answered my question:-

have you tried pressing the reset button if it fails to start?

Hi Mike,

Sorry. No, reseting does not work either.

Taking together all your suggestions it looks to me that I need a "better" power supply which produces a more constant power right from the begining (??) Any suggestion about its specs.?


PD. Right now I have it powered through USB and i works perfectly. What about these AC-DC adaptors which have a USB output (for charghing mobile phones)?

If pressing the reset don't work then it is not likely to be an issue with the power supply itself so you can rule out all those extra capacitor and better supply solutions. It looks like it might be the noise on the serial input line problem.

You see on of the disadvantage of posting in two places is that people don't have access to the full discussion.