To add storage capacity to my solar system, which is based on ENPHASE microinverters, I installed a MULTIPLUS II-GX inverter and PYLONTECH US 2000C batteries. When reviewing my application, CONSUEL confirmed that the battery side needed to operate as an IT system and that I needed to install an insulation monitoring device (IMD). I chose a DOLD 5881.12/100, which shuts down the inverter in the event of a fault. The diagram of my installation is here: 20261019 - solar installation diagram.pdf (46.5 KB)
I’ve run into a problem since installing it: the IMD is permanently in fault mode. It indicates a leakage fault on the negative pole.
I’ve carried out a series of tests to determine the cause:
Increased the trip threshold: No effect
Checked the insulation between the negative pole of the batteries and the chassis (which is connected to earth): No issues, everything is properly insulated
Checked the IMD with only the battery side connected (disconnected from the inverter): No issues, the IMD responds as expected
Checked the IMD with only the inverter connected (batteries disconnected): Permanent fault
Checked the insulation between the inverter’s negative pole and the chassis: Continuity confirmed, which seems to be causing the fault
Is it normal for there to be continuity between the inverter’s negative pole and the chassis (and therefore earth)? If so, I don’t see how I can connect my IMD. Has anyone encountered this setup before?
Hello, thanks for your help. Could the cause be related to an MP failure? Attached are photos of the connection area. I’ll run the tests over the next few days
Get an electrician to inspect the setup urgently. Those thin little wires at the battery connection aren’t fused, and to make matters worse, they’re routed together through the cable gland!
One chafed wire and the whole thing could go up in flames. The main input fuse won’t trip in this situation if the contact resistance limits the current below the trip threshold!
Hello, these small wires are what allow the CPI to take the measurement. Consuel didn’t raise any issues about this during its inspection. The CPI doesn’t accept a large cross-section on its measurement side (max. 2.5 mm²). But you’re right, adding a fuse in series on the line costs nothing. As for routing it through the same bulkhead grommet, I can indeed route it through the one on the left, which carries signals. Thanks.
Have you tried running the isolation resistance relay with the MP disconnected? For example by connecting it temporarily infront of the 125A MCB and leaving that MCB disconnected? If it still trips, then the issue is on the battery side, if it no longer trips, then the issue is on the MP side. (Its also possible that both sides could leak a small current which only reaches the trip point when both are combined, but that would definitely not be the first thing i would check for). In theory you could also just flip the 125A MCB off, and check if it still trips as is, but the MPs dont like running without a battery. So rather rewire to infront of the MCB.
Your schematic does not show the current installation status. There is a cable connected on AC-out but on your schematic AC-out is left unused.
Have you wired the batteries exactly as drawn? You should connect the main positive on one end of the stack while the main negative is connected on the other end. Not both on the same end as drawn in the schematic.
Lastly, the placement of the ET112 does look wrong in the schematic. Id guess the main load is connected at the bottom right in the main switchboard. So the ET112 cant measure that current. You need to place it at the same location as the Enphase mains CT is, on the mains side.
I guess you want the Victron ESS to charge whatever is left over from PV power minus load. So you set the Enphase system to full feed-in while the Victron ESS is set to keep zero feed-in. With the ET112 at the drawn location the Victron ESS will charge its battery with whatever PV power is produced, regardless of load, and it will not discharge the battery to supply a load when theres no PV.
Did you limit the AC input current according to your 16A MCB infront of the AC-in? Since if not, then its a bit undersized. The MP2 4k5 is rated 4kW for feed-in, which at 230V mains is roughly 17.4A. While charging it should not be an issue, since then the limit is the DC charge current of 55A, which is roughly 3kW on the AC side.
Im not sure about using the external CT for PV production. Possible that this works fine, but i think the external CT replaces the internal one of the MP, so the MP now measures PV production as its own AC-in power
Follow the hint of @M_Lange and use the original Canbus terminators. They contain an end resistor which is crucial for correct Canbus functionality. They are not just fancy blue port covers.
Hello, thanks for your reply and analysis. I’ll try to respond point by point:
-> Yes, I tried both configurations (they were actually among my first tests), with the IMD connected on the battery side and the circuit breaker switched off. No fault was detected by the IMD (I also measured the resistance between each battery negative and the chassis to make sure they were properly isolated; everything was fine, they are isolated). When I did the same test on the MultiPlus side (the original connection) with the circuit breaker switched off, a fault was detected, and when I tested the negative against the casing, there was continuity (I disconnected everything else around it to make sure of what I was testing). I conclude that the problem is indeed on the MP side.
There is indeed a cable connected to AC-Out, but nothing is connected at the other end at the moment; I’ve fitted WAGO connectors (I was planning to install some backup sockets one day, but that’s not on the cards for now. I need to check, but I think I disabled the AC OUT in software).
The batteries are wired as shown in the diagram.
I based it on the diagram provided by my equipment supplier. I did have some trouble configuring it, but I managed to get the system working. It will be difficult to put it next to the Enphase CT, as the panel is already quite full.
I managed to achieve this, although it required rather laborious configuration.
Yes, absolutely. I used the software limit provided by the MP. In any case, the line is protected by the circuit breaker (at worst, it would trip unnecessarily in the event of a software failure).
It was a pain to configure, but I eventually figured it out. In fact, my system was working perfectly during the testing phase, until Consuel asked me to switch the battery side to an IT earthing system and install an IMD (which detected a fault that had been invisible until then). I’m inclined to think there’s an internal fault in the MP, connecting the battery negative to the metal chassis and therefore to earth, which causes the IMD to trip constantly.
I haven’t noticed any problems with the CAN bus operation. I seem to remember reading that impedance matching wasn’t necessary. I put the caps on to keep out the dust. I’ll check this.
It must be terminated on each end, the system shipped with terminators, please make sure you install them and that the battery side is also terminated.
Regarding the connectors, I did find them — I hadn’t spotted them in the kit. I’ve connected them.
Regarding the insulation test between the battery’s negative terminal and the chassis, yes, I disconnected everything to avoid any stray loops, and tested with the device switched off.
