Electrical discharge in USB port

Hello everyone,

Recently, I got a generic Ethernet shield for my arduino Uno.

The shield - as you know- comes with a Wiznet W5100 whose tends to heat in normal use; However, I realized that it was too hot -in my opinion- , so I started to look for answers and I noticed that the laptop charger that I was using had only 2 prong so I tried with a 3 prong and it seemed to get the Wiznet a little bit cooler...

However, while I was doing experiments, my left cheek touched the arduino´s usb port ( the one next to reset button) and I felt a small electrical discharge, then I thought of using a 3 prong charger and the discharge disappear.

I have 2 questions:

  1. ¿Do you guys think that the electrical and heat problem was because of a lack of ground?
  2. Due to the fact that sometimes I do not have a pc at hand to power the arduino, ¿ could I use an Iphone 5 charger (output 5V & 1 A)?

I´m concern about amps cuz I have heard that what´s important in chargers is the voltage and that I the charger gives you more amps that the load needs it does not matter because the load will use only the amps needed...

Any thoughts ?

Thanks in advance,

:grin:

This could be one of two things:

Capacitive leakage from the switch-mode supply causing a small AC current which you can feel - not unknown and is a consequence of unpolarised 2 wire mains connectors on the switch-mode input. You can try reversing the 2-pin plug.

Or it could be a faulty and dangerous unit.

Using 3-pin plug would be advisable I reckon.

The temperature of the Wiznet chip is a red-herring, it will be hot it takes something like 150mA as its driving ethernet which is power hungry. Check the USB 5V rail with a multimeter if you like.

03ed: The shield - as you know- comes with a Wiznet W5100 whose tends to heat in normal use; However, I realized that it was too hot -in my opinion- , so I started to look for answers and I noticed that the laptop charger that I was using had only 2 prong so I tried with a 3 prong and it seemed to get the Wiznet a little bit cooler...

Did you measure it with a thermometer? I think the "cooling" was probably in your imagination.

03ed: 1. ¿Do you guys think that the heat problem was because of a lack of ground?

No.

03ed: 2. Due to the fact that sometimes I do not have a pc at hand to power the arduino, ¿ could I use an Iphone 5 charger (output 5V & 1 A)?

Yes.

03ed: I have heard that what´s important in chargers is the voltage and that I the charger gives you more amps that the load needs it does not matter because the load will use only the amps needed...

Correct.

03ed: Any thoughts ?

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