Ethernet Shield does not work with external 9V power supply

Hi, I have an Arduino Mega and an Etherned Shield. Both works great together, if I have connected the board to my PC via USB cable.

But if i connect the board to my external 9V power supply just one red LED lights up on the ethernet shield. The shield does not connect to the network :/...

Can you imagine what is wrong with my board / shield?

Thanks!

PS: I noticed that when i use an battery pack of 4x1.5V (AA) it also works. Is it possible that 9V are too much?

does your 9V battery deliver enough current ?

Oh my God. I noticed that the output of the power supply gives me AC :O. I can be happy that the board is not defect I think :/... the current is 400mA. this should be enought? But that it is AC and not DC is a problem I think

Now add 4 diodes and 1000+ uF to get 10…12V DC

rect-bridge.jpg

Thanks for the reply!

So its no problem to insert ac to the arduino board? Or do I have to change the AC to DC before i connect it to the Arduino?

Knut just told you the solution Use 4 diodes and a capacitor to make a recitifier. That turns the AC to DC