Offgrid MP2 15000 + Autotransformer 240/120v and can't get MP2 to engage the Ext Gnd Relay

Q&A and troubleshooting
, , ,
1

I have an off-grid setup in the US with a Multiplus-II 15000/230v wired to the Victron Autotransformer (100a) and can’t get the MP2 Ext Gnd Relay wires to engage the N<>G relay at the autotransformer to bond split phase N to G vs the MP2 bonds 240v N to G. In this split phase setup you can’t bond N or L at 240 on the MP2 to ground and the way I have it wired matches https://www.victronenergy.com/upload/documents/Datasheet-Autotransformer-32A-and-100A-EN.pdf Figure 1: Split phase supply for unbalanced load (Ground relay of autotransformer should be used)

Two test scenarios i’ve done, both not working as suppose to…

  • Manually provide 24v to the auto transformer and the yellow light turns on showing N to G/PE its engaged, fluke meter confirms, voltages are good and powers the house just fine, including GFCIs. VE Config / Grid profile is Other:AC Neutral path externally joined (VE Config / Inverter tab shows Ground Relay not checked, which means should be disabled)
  • Setting grid profile to Other: Not compliant to any grid code standard (VE Config / Inverter tab shows Ground Relay enabled) - The MP2’s 240v N is bonded to G and not seeing 24v at the Ext Gnd Relay or even a flicker when wired to the Autotransformer and its on too incase its sensing for continuity for internal/external. (Autotransformer obiously not wired with ground to test to prevent conflicting 240v N to 120v N getting cross/bonded if both relays engage. Apparently the newer MP2s should auto select internal vs external if external is wired? I have no DIP SW1’s internally I can find to turn on/off unless I missed them.

Is there a setting I’ve missed either physically on the MP2 or Autotransformer or in VE Config to enable the use of the external ground relay and disable the internal relay?

2

This isn’t exactly the scenario described, but I too use an MP2 (8kVA 230V) with Autotransformer in N.A. to produce 240V split phase. In my case, N - G bond is in my main load panel, so MP2 ground relay is disabled, as is the Autotransformer ground relay.

External AC is provided by a Honda EU7000is, with the L1 and L2 connected to L and N on the MP2 AC input. The Honda’s Neutral is not connected.

The system works without a hitch.

3

Which grid profile are you using? I assume Other: AC Neutral path externally joined and not using the internal or external relay and also not using the auto transformer relay too, right?

When I do a generator, it only accepts the “grid” when I use Other: Not compliant to any grid code standard which when generator is off, the MP2 bonds N<>G. The externally joined profile switches on/off of the generator like its unacceptable under this profile, which makes 0 sense. Its a GenMax inverter style generator 10.5kw and if its set to full speed or variable speed control, doesn’t make a difference. Only errors I see in my CerboGX is grid lost. Is there a deeper level of logging I can see like not able to sync frequency or ground fault or something else?

Your setup is similar, I’d like to have a generator as backup during summer months and weeks with bad weather… Likely pulling the trigger on 25kw Generac with 250gal diesel belly tank, but thats “phase 2” :slight_smile: That will be grounded once installed, likely similar to my existing problem.