After testing the charge mode for almost 3 hours, eveything is fine (relay heating up a little but nothing abnormal, no heating at all on the wires), so I am charging the whole day today
To spread the battery power, each grid tie inverter DC side is connected to its neighbor with a 2.5mm² solid core cupper wire and I may need to double it for the first ones
Also an heavy gauge black cable has been connected from the negative battery pack terminal to the negative DC terminal of the grid tie inverter in the middle of the stack
Testing the inverter mode: I thought everything was going fine, until being under 0W, pushing power outside my home grid, Wattson glowing green and showing - 150W, the grid tie inverters should start to shut off one after the other; But here, nothing for several minutes !? Something was wrong ...
I thought the Blue/Red/Green signal coming from Wattson was affected by the proximity of other live wires and started to move the voltmeter, etc... but nothing changed
It made me think of my Arduino power supply problem 2 weeks ago: Supplying 12V from the battery pack through a ebike.ca 72V to 12V DC-DC converter, I had the same problem
Here I was using a 12V/24V to 5V DC-DC converter (from a car lighter socket USB converter) to power the Arduino board and it looks like it was the source of my problem:
I then disconnected the USB cable from this USB DC-DC converter, and used the 220V USB hub power supply instead, and everything was back to normal ! Interesting ...
Conclusion: It looks like the Arduino board does not like any DC-DC converter with the battery pack as a power source !