A Multiplus II shows negative AC output wattage in a Parallel Split-Phase system when grid on only

DIY
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1

The configuration here is used for an RV. It is split-phase parallel of 4 Multiplus II 48/3000’s. The slave of L2 is showing negative wattage when trouble shot with L1 master and L1 slave to verify the problem. L2 master works fine with L1 master and L1 parallel. If the 4 units are running as a whole as configured, when grid comes on, Cerbo GX shows L2 AC loads drop. The wattage drop varies with the load applied. When the grid is dropped and it stays in Inverter mode, L2 wattage returns to normal.

There is no configuration I’m aware of that would cause this. Ground relay is verified as only on L1 master. Both sides of the AC in and out have identical length and gauge. Here’s the thing. I’m not so much worried about fixing this inverter because I’m pretty positive that it just needs to be repaired. I am more concerned about something in the VE bus monitor. While I was troubleshooting the negative AC thing I found that when it is in inverting mode, it indicates L1 and L2 out of phase. When the grid is turned on, it accepts the connection and VE bus drops the “not in phase” warning. I verified this in every split-phase configuration: L1 and L2 full units, L1 Mast and L2 Mast, L1 Mast and L2 Slave, L1 Slave and L2 Mast, L1 Slave and L2 Slave. When the grid comes on they’re on in phase and inverting is out of phase. All connections were checked and are connected to the right phase.
VE configure 3 is up to date and all units have updated firmware.

Is there a bug in VE configure causing this? Without an oscilloscope I’m not sure of a way to check the phase. The in junction box is identical to the out junction box. I doubt the bad L2 slave inverter is causing this reading. That’s the only thing I have not done is remove the connection from each junction box to see if somehow it’s influencing it. Ideas?

2

Can you show us the VESystemConfigurator main screen, and then click on each inverter to see if it is assigned to the correct phase correctly. You should track each unit by serial number and triple check the ones you’ve configured are what you think they are.

3

UPDATE: So, after taking the inverters back to stand alone mode and then reconfiguring the whole set, the VE bus monitor fixed itself and now indicates correctly being in phase in both invert and grid mode. I was unable to trace the bug or repeat it.

@ Rick In the prior post I had checked each inverter for the correct phase assignment and verified LED blinking in conjunction with wiring, which all checked out. The error might have come from the multiple re-assignments I made while troubleshooting the negative wattage problem.

As a byproduct though I now have multiple device listings that have L1 L2 L3 device numbers listed through the Cerbo’s Inverter → Device → Serial Numbers menu.

Ghost Devices
Ghost Devices1046×516 79.2 KB

I know I’ve seen this before but I can’t remember what the cause was and how I fixed it. The number of multis also was showing correctly.

Ghost Multi 2
Ghost Multi 21046×516 59.5 KB

4

Great!

Is there a “Remove Disconnected Devices” option at the end of the devices list?
I’m running GUI v2, and my memory isn’t very good.

5

Sorry for the late reply. Unfortunately it doesn’t. However, the system seems to have taken care of that automatically because all the false listings are gone. The “number of multi’s” listing is still blank. I’m guessing the VE bus network will take care of it eventually but it must be a slow process. I have used the option to “Re-detect VE bus” and “Restart VE bus” options as well and that didn’t make a difference prior to the system just updating itself. For the most part I’m unconcerned at this point. I’ll just be contatcting my supplier to have them work in the faulty multiplus.