Multiplus 3000W 230V 120A 50 & Generator

Q&A and troubleshooting
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1

Complex AC and bonding system on a yacht; interaction between the PE (Protective Earth) paths, a Isolation Transformer, a Rotary Switch, a MultiPlus, and a Generator

Concern about the Multiplu’s cyclic rejection of generator power and the PE paths during inversion-

1. PE Paths and Bonding System Current Setup,

PE Bar #1 connects:

  • Isolation transformer output (PE IN = PE OUT, 0Ω)

  • MultiPlus input

  • Air conditioners

  • Generator

Bonding Bar #2 connects:

  • Battery negative

  • All metal masses on the boat (isopotential) Before Interconnect PE Bar #1 and Bonding Bar #2, to eliminate potential voltage differences between the AC and DC grounding systems.

Timing and method matter.

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2. MultiPlus Behavior and Generator Rejection

OBSERVATIONS

- Cyclic rejection of generator power only occurs when:

  • The generator is the source.

  • Air conditioners are running.

- No cycling occurs when:

  • The transformer is the source.

  • The generator is the source but air conditioners are off.

  • The generator is the source, the inverter in in “charge only”, snd the Air Conditioners are runing.

POSIBLE CAUSES:

A. PE Path Differences During Inversion**

When the MultiPlus inverts, it disconnects the source PE (from the transformer/generator) and bonds its output PE to neutral.

This creates two separate PE paths:

  • Air conditioners: PE → Generator → PE Bar #1.

  • MultiPlus output**: PE → Bonded to neutral (floating relative to generator PE).

As PE Bar #1 and Bonding Bar #2 are not interconnected yet, this can create a potential difference between the generator PE and the MultiPlus output PE, leading to:

Ground loops

Noise or voltage fluctuations

The Multiplus detecting “poor energy quality” and cycling

B. Generator Power Quality

- Generators (especially AVR types) can have voltage/frequency fluctuations under load.

- The MultiPlus may be sensitive to these fluctuations, especially if the PE reference is unstable due to the split PE paths.

C. Load Imbalance

- Air conditioners are inductive loads and can cause voltage drops or phase shifts.

- If the generator struggles ( not the case it is 12 KVA)with these loads, the MultiPlus may detect instability and switch to inversion.

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Recommended actions?

2

Check the IP log of the multiplus (Using VE configure) to check the reason for disconnection. Could be under voltage / underfrequency. you could be getting very short voltage drops as the Aircons cycle.
The two ground busbars do need to be connected.

This is not likely to be ground loops.

3

I agrre with Mike that its more likely caused by the generators voltage/frequency not being stable enough on load spikes and thus the MP rejects it.

But,

are you sure thats correct?

Usually an isolation transformer also isolates the incoming shore power PE from the rest of the hull. The incoming PE is connected to the core of the transformer, the boats own PE is connected to the transformer housing

Permanently connecting the two can lead to electro-corrosion on the hull or RCDs tripping on the shore side

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