Again - ESP32- POE getting to hot?

[kr0815]

we do a Project with many ESP32-POE - found out now it get´s to hot when installed in a an eclosure and powered by POE
We have some Boards with Revision G - more with Revision I - both have the same Heat problem

we are thinking now about installing a fan

What is this miracle with the 2 resistors that are responsilbe for a minimum POE Load?
As we understand they transform about 6W in heat?
I ee these resitors only in revision G - but revision H makes the same problems?
In circuit diagram of revision I POE part - - something is written - i guess it´s bulgarian - what does it mean?

Thanks

[LubOlimex]

ESP32-POE and ESP32-POE-ISO had always been relatively hot boards when powered from PoE. These are relatively small boards that have to convert 50V to 3.3V, there is no way to do it without some heat dissipation.

However, revision I of ESP32-POE changes the design from 2-layer PCB to 4-layer PCB. This is huge upgrade and should lower the overall temperatures and allow for better current draw.

The notice in Bulgarian is a mistake. It is about R33 but you can ignore it, it is left over note to the manufacturing department but it is left over from previous revision and no longer applies for revision I.

[kr0815]

thanks for your answer

we found out that biggest problem is the 4.7K resistor R42 that assures the 10mA min Power for POE - it burns 0,5W - which is much for such a small board - especially when put in a enclosure

we are thinking about removing it - since we draw incl. the ESP32 about 18mA minimum without this resistor

We don´t have much experience with POE - safest way would be to add a relais that keeps this resistor inline untill the boot process is over - do you think this is neccessary?

As it is a project with over 200 ESP32-POE - we have to be sure it works 100%

[LubOlimex]

You can't remove R42. Doing so will probably break the PoE connectivity since there is minimum power signature of 10 mA in IEEE 802.3af/at.

If you are looking to make 200-units, I'd recommend to also test the ESP32-POE-ISO, if you haven't already. It might behave better for your project.

[kr0815]

R42 draws about 0,5W - Do you think we get Problems if our attached Hardware already consumes 1W?

We were thinking abouz the ISO-Version - but it doesn´t have enough current for the project and it´s to large :-(

[LubOlimex]

1W total is fine. Drawing up to 3W (excluding 1W for board needs) in total when powering via PoE is fine. I've written this in the FAQ section:

The PoE circuit can safely provide up to 4W, i.e. 800mA @ 5V. Part of this wattage is used to power the ESP32 module, the battery charger, and other circuits part of the board design; the remaining wattage is available for additional circuits (up to around 600mA).