Hey guys,
I want to power an arduino ethernet board and I have a AC adapter 12V 2.5A - is it safe to use?
Cheers!
rcoor:
I want to power an arduino ethernet board and I have a AC adapter 12V 2.5A - is it safe to use?
Yes. If is has a barrel plug that fits the Arduino barrel jack you can just plug it in. If that doesn't work the power is probably reversed (don't worry, there is a protection diode that prevents that from hurting the Arduino). The center pin should be Positive and the barrel should be Negative.
Warning: If you use the Vin pin instead of the barrel jack, that bypasses the protection diode! Getting the polarity wrong then can damage the Arduino. Make sure it is the + side connected to Vin and the - side connected to Ground.
First of all, if you have a voltmeter, check that it delivers no more than 12V . I've seen cheap adapters labelled Output 12V DC that gave 17V !!
If it is 12V, it will work, but there will be about 1,5Watt dissipated by arduino's regulator, it will get hot 
The ethernet shield needs between 150 and 180mA itself, if you add the arduino and a few devices (leds, whatever...) , you'll quickly be around 200mA or even more.
(12-5) X 0.2 = 1,4 Watt
I always prefer to put an external 9V regulator between the 12V and arduino socket . You can use linear LM7809 reg. or more efficient switching DC regulators.
This way, if we assume 200mA , the power dissipated by the arduino reg. is (9-5) X 0.2 = 0.8 W
rcoor:
I want to power an arduino ethernet board and I have a AC adapter 12V 2.5A - is it safe to use?
As long as it puts out DC, not AC. If it says "12V AC" it isn't suitable.
rcoor:
I have a AC adapter 12V 2.5A
Remember the current is only what it can provide not what it will provide.