Good day,
I have the following setup.
4 x Multiplus2 5000 inverters (split phase setup, 2 on L1, 2 on L2)
CerboGX
5x SOK 48v 100ah batteries with comms. to Cerbo
24kw Marathon/Kubota Generator
24x Canadian Solar 400w panels, roof mounted ~30° tilt, south facing.
450/200 charge controller (2 strings 10 panels, 1 string of 4)
Tigo TS4-A-S Modules, per panel.
I initially was running on 2 inverters without any issue, decided to add 2 more for redundancy, and additional charging capacity. All wiring (DC and AC) for the inverters are the same length with a tolerance of 1/2" or so. The problem I’m having is what seems like partial comms between the second set of inverters and the rest of the system. When disconnecting the generator, the first set of inverters, I call them 1.1 and 1.2 will disconnect and wait for the generator cooldown/wait condition to be satisfied. The second set (2.1 and 2.2) will disconnect, but not wait for the timers to expire, sense the AC from the generator on ACin 1 and reconnect as chargers, causing 1.1 and 1.2 to do the same until the frequency falls, from the generator physically stopping causing them to disconnect. Sometimes 1.1 and 1.2 will take lead, putting 2.1 and 2.2 in standby and the cerbo will show “Inverting” as it should. Other times, 2.1 and 2.2 will take lead, and the cerbo will show “unknown” for inverter status, but everything functionally is working. I’ve replaced all the Ethernet cabling between them with factory made patch cables to rule out a bad crimp- no change. All 4 inverters show up in the cerbo as I would expect. I have configured them all the same and updated firmware through the MK3 device.
I’ve attempted to troubleshoot this with my vendor through VRM and don’t seem to be getting anywhere. Has anyone run into this? Could it be a VEbus comms issue in 2.1 or 2.2?
Update 1:
I just tried a load test to hopefully get the second set of inverters to go online. They did not- the lights indicated standby, but no issues with pulling 13kw for a few minutes, which is a bit above the expected ~10kw rating of the primary set of inverters. Load was mostly resistive- oven and dryer, so the power factor should have been pretty close to 1.0.
Update 2:
Had the need to run the generator today. Did some testing while running with interesting results:
The generator feed comes into a sub-panel (MCB) and is distributed to the MP2s with 2x 2pole 70A breakers (1 for L1/L2 on inverters 1.1 and 1.2 respectively) and one 70A 2pole breaker for 2.1 and 2.2 respectively. The generator started, the chargers came online and the Cerbo was showing ~250A charging- about what it normally does. I got the ammeter out and checked flow. 1.1 had ~60A on ACin, and 30A on ACout. DC amperage at 1.1 was ~62A.
Here’s where it gets weird, on 2.1, ACin was showing 0A (verified meter was on AC), ~30A on ACout, and ~62A on the DC side.
This leads me to believe that it is pulling power from the A/C side of the system and using that to charge. I verified that both in and out are showing 120V LtoN.
I have unchecked the ground relay box on inverters 1.2,2.1, and 2.2.
When the run timer is up on the generator, the Cerbo indicates a stop, and it goes through a cooldown cycle (90s) followed by the cooldown cycle (180s). Shortly after the inverter contactors release from the generator, 2.1 and 2.2 pull back in (indicated by bulk charge lights and green inverting lights) causing charging to resume with 1.1 and 1.2 indicating standby, but cerbo (smart shunt) indicating 250A of charging. Amperage on ACin of 2.2 is now at 65A. Again, with 2.1/2.2 in lead, the cerbo indicates “Unknown” status on the inverter. The inverters again release the A/C in contactors when one of the low limits are reached as the generator shuts down, presumably frequency, but possibly undervoltage.
Thanks for taking the time to read, and thanks in advance for your insight.
Edit: Add equipment/details.
