Scenario:
a) MP2 and MPPTs --- Lynx --- Smart Shunt --- MCCB --- Battery
Or
b) MP2 and MPPTs --- Lynx --- MCCB --- Smart Shunt --- Battery
The smart Shunt should act as a battery monitor on Cerbo GX. The MCCB is used to break the line manually or if certain real bad circumstances occur.
Should the smart shunt be before the mccb or after?
I would have it right by the battery before the disconnect. And ideally it needs to be closer to the battery for accuracy you can get volt drop through a disconnect.
It can be installed after the mccb there is a setting where it keeps it's last SOC on power up.
It has its own fuse. So would be safe before the disconnect and is not a high draw item.
I wonder what happen, if the shunt is between Battery and MCCB and if the MCCB disconnects. The shunt is still able to measure the Volts of the battery and would tell MP2/MPPT via the Cerbo the current Volt. Would MP2/MPPT try to load the battery or get power from the battery which would technically not be possible as the MCCB has disconnected? Does MP2/MPPT detect this failure or take damage?
The shunt will remain powered on.
The MP will switch off unless on mains or possibly the solar keeps it alive.
If in the event the mccb trips, the inverter and mppt remain on, and a larger load switches on then you will likely see DC ripple. Prolonged DC ripple will mean damage.
Just FYI I have seen systems (with lithiums' whose battery contactors disconnect the battery and still send 'battery voltage' information to the GX and the system remains powered on but mainly because there is mains voltage or huge solar.
So the scenario you described is not unlikely or unheard of.
If you prefer a different set of information, run the shunt the other side just check the voltage though on the battery terminals vs the shunt ( under load and charge) to be sure you are not going to be in the situation of undercharged/over discharged batteries.
Actually, if I have a look at my Cerbo which displays Volts/Current of Multiplus, Shunt and BMS, there are nearly the same. Just 0,07 diff and I'm loading the 18s LiFePo4s 'just' to 3.45V. I guess, in this case placing the shunt between Lynx and MCCB is a little bit better because then the shunt can detect if the MCCB has disconnected and provide this information to Cerbo. In such a situation with 0 Volts on the line because of the disconnect the Multiplus2 and MPPT would hopefully turn off, throw an error which is what I would expect.
Does this make sense?
No, it's not making sense. The Shunt itself doesn't measure Voltage, this comes from it's separate power supply cable, which can be located wherever you want (usually right on the battery +). The Shunt itself is always positioned on the negative battery connection, not the positive.
The positioning of the Shunt relative to the MCCB is only relevant if you're using a double-pole MCCB, switching both +ve and -ve. Perhaps you're not?
If only switching +ve (which is very common), then whether the Shunt comes 'before or after' the MCCB doesn't apply. They're on separate cables.
This needs to be clarified to ensure you're getting the right advice..
The MCCB connects/disconnect both (+ve and -ve)
The shunt could be between MCCB and Battery (the -ve) and the plus cable (+ve) could be between MCCB and Lynx. Or another 'don't do that'?
Ok, 2 pole. The Shunt can go anywhere on the batt -ve. It's little power-suppy/V-probe is optional in the sense that it will power down if it sees no V. You wouldn't actually see batt V at the Lynx, but might see short spikes if something is still offering charge, then the charger would control to the non-battery V (but not charge).
Up to you, but I think I'd rather see the shunt not power down. So the probe on the battery. Mightn't suit you or your system though.
