Works great over USB, but not with wall wart!

I am using a mega and a seed ethernet 2.0 shield. When the mege is hooked up to the computer over the USB, everything works great. When I try using a power supply, the mege will not go back online and the square 5200 chip gets very hot. I have tried 3 different power wall warts; a 12V @ 2A, a 9V @ 9mA, and a 5V @ 1A. Any suggestions, am I doing something wrong?

What’s the polarity of your wallwart? Does it match that of the Mega’s input?

The center is positive, is that what you mean?

Yes - should be tip +ve, case (or ring) -ve. Presumably the wallwart powers other devices correctly? What happens if you disconnect the ethernet shield? Are you able to power the Mega from a USB cable plugged directly into a 5v USB charger? IOW let’s try to isolate the root cause - is it the wallwart, the power jack, or something else?

I’m just using the wallwart to power the mega/eithernet shield. Nothing gets hot when I power just the mega. Event when I plug the USB cable into my 5v USB charger, the 5200 still gets very hot and the mege will not go online. The 12v wallwart has the center positive type connector, same with the 9v (I’m going to say the 9v power supply does not have enough power, it only puts out 9mA), and the 5v is a USB charger. By the way , thanks for the help.

I don’t know a whole lot about the ethernet shield, but is it possible it only needs 3.3V? Typically overheating is a symptom of too high a current or voltage, or inadequate power dissipation. When you’re powering from the laptop, it’s likely you’re only supplying 0.5A.

I suspect it’s a ground problem. Usually the PC has a 3-prong plug and it’s USB ground is the real earth ground. Two prong adapters don’t have a ground, so the black wire coming out of the adapter is not equal to the PC ground, and since there is a voltage difference current flows through the USB lines.

It is easy to kill chips like this. If your chip is still working, you are lucky (especially if it got hot - that is a lot of power flowing through it!).

Sometimes you can fix this by using a good USB cable that has a nice ground connection between the two metal shields. But often it’s better to avoid these bad adapters. Often laptop adapters have 3 prongs, and are a little better behaved than simple 2-prong phone charger adapters.

And last, make sure your PC and adapter are plugged into the same socket or power strip. Sometimes a cheap adapter on the same power strip as PC will work, but it’s no guarantee.

Good luck!