Ethernet with WIZNet 5100 / ENC28J modules freezing


I am connecting Arduino Mega to network for communication with MQTT broker.

I tried two different ethernet modules (both small board, not a whole shield) - WizNet5100 (funduino) and a ENC28J module.
I have 2 pieces of each module and 3 Arduino Mega compatible boards (tried different combinations).

On one of the 3 Arduino mega board it works OK with ENC28J. On other two boards that I have and have tried I have the same problem with both WizNet & ENC modules.

If Arduino is connected to USB (To computer or USB Power Adapter) it works OK
If Arduino is connected to 12V power supply (tried two different switching PS) trough jack socket, then after a minute the connection crashes.

I found out that the voltage on the 5V pin of Arduino slowly drops under 4V even to 3.5V and that's why everything crashes.

Furthermore the voltage regulator on the Arduino (near to jack socket) gets very hot (I cannot hold the finger on) - so I suppose this is the problem.

After I have installed the heatsink on the regulator, the connection is quite stable and doesn't crash. But this doesn't feel to be a stable solution for a long-live system.

Is this normal? Do this modules draw so much current? I only one DS2018 to measure temperature and send it to MQTT - NO other peripherials connected to Arduino. The behaviour is the same even if I do not connect the network cable.

Do I have to power this modules separately? Any suggestions?



You proved that the problem is the voltage regulator dissipates too much heat.

Two solutions:

  • Use 7v to 9V not 12V for the external power
  • Power the ethernet module separately from separate 5V supply

See this page about voltage regulator issues:

Thank you for your answer.

Yes, I proved the problem, but I wondered if also somebody else has similar problems with this modules and voltage regulation. As I read on the link I see that there are indeed issues with regulator.

I bought only 12V and 5V power supplyes :(, and it is a bit messy to have more power supplyes for one device. Mybe I have to add a switching step-down circuit to my project and from there power the eth modules.

In case of using 12V PS to power Arduino and 5V PS to power modules, do I have to connect grounds together?

What about powering Arduino from 5V power supply - directly to 5V pin, is this a good idea?


What about powering Arduino from 5V power supply - directly to 5V pin, is this a good idea?

From posts here on the forum, it is not a good idea. It has been known to brick the usb port.

use a 9 V power supply for Arduino and power the module from 5 V pin of Arduino.

I took 12V PS on purpose, because I have also a 16CH Relay module that needs 12V.

So I have to figure out now the least messy solution.

Thank you.

I took 12V PS on purpose, because I have also a 16CH Relay module that needs 12V.

So I have to figure out now the least messy solution.

Thank you.

is it really 12 V? 12 V shouldn't be a problem, but if it is a little more, it can be to much for the ragulator

Exactly 12V, after cable loss it gets 11,98 to Arduino... I can set a little less (finetuning).

What I always do and recommend is to not power anything from the 3.3V or 5V connections from the arduino.
I've blown up several arduino up due to the internal power regulator melting. Plus I found the 5 and 3.3V connections of the Arduino to be not all that stable, it is a very small not cooled regulator on there.

It is ok to power some small senors through the Arduino, but still get a multimeter out and measure the overall current consumption on the 5 or 3.3V connection. I found out that anything over 50mA for several seconds will overheat your Arduino. Ethernet modules typically consume up to 250mA.

What I do is to get a 7 to 12V DC adaptor, because they are cheap and readely available, to power the Arduino and use a DC-DC step down regulator powered by that same adaptor to create a seperate 5 or 3.3V supply line. Or 2 step down regulators if you need both voltages. Don't forget to tie all your ground connections together or you can get strange results.

Anyhow, my 2 cents on how I experienced the best way to power an Arduino project and keep everything nice and cool.

3.3 V pin has 50 mA max in the standard Uno specs. 5 V pin power depends on Vin and regulator.

Hi, There is another perhaps easier solution: A UNO derivative that has advanced power supply regulators:

This has:

  • Advanced Power for your designs with new onboard 5.0V and 3.3V power supplies.
  • Earlier Arduino versions had only 50 mA of current available at 3.3V but now RoboRED provides up to 500 mA at 3.3V
  • An advanced 5.0V switch-mode power supply onboard the RoboRED provides MUCH more 5V power than the original: up to 2 Amps (2000 mA) to power many servos or Relay Boards or powerful LEDs, etc. And the Input Voltage rating is higher at 7-23V


More info HERE

DISCLAIMER: Mentioned stuff from my own shop...