I bought a ethernet sheild and when I connected it to my arduino uno and plug it to my computer i notice the wiznet chip on the ethernet sheild became too hot , what is the problem? is it normal?
Yes, they get quite hot and draw about 200 ma to get there. You're not the first to be concerned.
I quickly disconnected my WIZ810Mj module the first time I fired it up.
I have four Ethernet shields (with POE) that are used outdoors but not in direct sunlight. I would guess the temperature at noon is roughly 35C (95F) or more. The plastic enclosure gets warm to the touch but they seem to be running fine so far.
Three months later... and two of the four Ethernet shields (with POE) have died. I don't know if it's due to the high temperature and humidity, or if it's because ants got into the POE switch. =(
I have found information that indicates that POE voltage has a broad range. I think the voltage can be anywhere from 24 to 56 volts. You can by POE power supplies at many different voltage specifications.
On a side note, Cisco switches with POE put out more voltage than Linksys switches that I have seen.
More voltage = more heat.