I am adding a third Smart MPPT charge controller to my teardrop trailer and now need to use DVCC to limit the maximum charging current. I also have a BMV 712 Battery Monitor, a BlueSmart IP65 Charger (shore charging) and an Orion-Tr 12/12-9 DC-DC Converter (charging while towing). My battery is a 100 Ah lithium battery that has a BMS for overcurrent and thermal protection200, but it will not communicate with a Venus OS device.
Any two panels at full power will be under the maximum charging current, but three at full power would be over the maximum charging current.
For cost and physical size issues, I plan to use a Raspberry Pi running Venus OS with four USB to VE.Direct cables.
In most circumstances, I could get away without DVCC, as I only plan to use all three solar panels when it is cloudy/shady, and the panels will only be operating at 10-30% of rated power. I currently have all MPPT controllers configured with VE.Smart. It works great with two panels. I have not tested with three.
There are two cases when I do need DVCC: 1) when the sun comes out and all panels are putting out rated capacity and 2) when it is full sun and I want to plug a Jackery into a 12V outlet in the trailer and charge it inside the locked trailer while we are away.
Since I don't need DVCC at night, I've thought about powering the Venus OS device via one of the solar panels in parallel with one of the Smart MPPT charge controllers. The power draw overnight of the Venus OS device would amount to several percent of the battery capacity which would be a problem for a multi-day stay in cloudy/shady conditions.
I have several questions:
0) Am I over thinking this and should I just never put the panels in a straight line so they never hit full capacity at the same time?
1) Would I have a ground loop/isolation problem with the Raspberry Pi via the power and USB connetions? I assume yes, which is a show-stopper for this configuration.
2) If I used a Cerbo-S-S GX or similar, would I have a ground loop/isolation problem via the power and USB/VE.Direct connections?
3) At sunrise, there could be a race condition where one of the panels reaches sufficient voltage to start operating before the Venus OS device starts operating. If the Venus OS device comes up after two panels, will it take over coordinating charging? I should not have an overcurrent problem because the Venus OS device will start operating at a lower voltage than the parallel MPPT controller.
4) At sunset, there is a similar race condition problem. If the power supply panel and Venus OS device powers down before the other other two panels, will those two MPPT charger controllers just revert to single-controller operation with the possible problem of switching to absorption or float voltages independently? I won't have an over-current concern in this case, because the Venus OS device will stop operating after the parallel MPPT controller shuts down.
5) Assuming I have to connect to the battery for power, are there low-power modes that would make a Victron Venus OS device a better choice than a Raspberry Pi?
6) Assuming I have to connect to the battery for power, is there a way to set the Venus OS device to wake at sunrise (or a set time) and power down at sunset (or a set time)?
7) Is there a difference in power draw of a VE.Direct port on a Cerbo-S GX vs. a USB port?
8) Under Raspian OS it looks like I can disable some interfaces (Ethernet) to reduce power consumption. Is there a similar way to do this in Venus OS?
