The CAN bus itself does not specify a power supply. CAN Bus is just about the two wires with differential data lines.
The heatpump provides the 16-18V power supply for the WPMi (that control display on the pump device itself) and additonaly for the external control panel “FEK”.
I am investigating more… If I connect the power of my CAN device at run-time (not recommended! ) it works. If I make a cold reboot of the heatpump by triggering the RCD, it does not work.
Maybe it just needs some slow-start stuff (activate the WLAN after 3min in case of a cold boot or sth. like this)
@ mkai What a coincidence, I wrote under another post, virtually exactly the same idea and am also working on my own board, but specifically tailored to the problem Stiebel and FEK.
The software / proof of concept WPM3 and FEK run error-free for a week although I change the data on the bus. The problem with the power supply I had with the WPM13 also. More than the FEK and it breaks down immediately. Therefore the idea was POE, external 12-48 volts or 230V to use. To use directly the supply voltage of the controller would be best, because thus everything runs through a fuse and starts at the same time.
It seems that quite a few people are actually addressing the problem. Perhaps one should bundle the resources or connect the posts. My background would be a master in computer science, so the programming work would not be a problem. With the PCB design I am not so experienced.
Why do you suggest POE? I currently run the PCB with 5V and it is very stable
I had many thoughts on implementing POE stuff on PCBs, but altough there are many open source arduino PCB examples, the effort to get all the parts assembled from a PCB manufacturer like Jlcpcb was to high. Pricing more than 200€ / 5 Pcbs.
Btw. I created a discord channel for this project, maybe a good place to directly exchange ideas on PCB design
I stumbled accross your PCB because I search one for my project.
I will install a modern car multimedia head unit in an old camper which has only legacy 12V signaling. I wrote an ESP application which will control the head unit via CAN.
I need at leat four 12V capable GPIO inputs to have no extra wiring. They should be protected with for example TVS diodes to avoid damage through voltage spikes during cranking.
Is it possible to include these in your new PCB design?
) it works. If I make a cold reboot of the heatpump by triggering the RCD, it does not work.