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alaskannoob avatar image
alaskannoob asked

How many Victron Autotransformers can be connected to a single Multiplus II?

If I have a single Multiplus II 230V supplying single phase power to several different locations on my property, how many Autotransformers can I have at each location to split the power into individual breakers given that a relay is required from inverter to Autotransformer? Can other relays from the Cerbo GX or MPPT RS in the system provide the relay to the Ground Relay of additional Victron AutoTransformers?

Autotransformer
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Mike Dorsett avatar image
Mike Dorsett answered ·

you could use one slave relay driven by the Multi, to control the other Autotransformer relays.

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alaskannoob avatar image alaskannoob commented ·
That would be great. From what I understand, somehow, the inverter through the relay to the AutoTransformer shuts off power to that Autotransformer when it overheats or has a fault or something. So using the slave relay, when the Multi senses a fault with one Autotransformer, it would just stop supplying power to both Autotransformers I suppose. It also does something with grounding/bonding to solve the issue with 230V single phase power, but I don't think that's an issue for an off grid installation so perhaps it doesn't matter for our case.


Thanks for the info.

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klim8skeptic avatar image klim8skeptic ♦ commented ·
@Mike Dorsett It's probably best you know that the AT will be 700' from the multi.
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Mike Dorsett avatar image Mike Dorsett klim8skeptic ♦ commented ·
OK, So to avoid extra wiring, it would be possible to ignore the relay.

This obviously depends on what earthing / PE scheme you are using, also on whether the 240V is used, or just there for distribution.

1) If the 240V is just for distribution, you can configure the multi to disable the internal ground relay. This will result in a 'floating' 240v system, and the Neutral point of all of the auto transformers can be hard wired to ground.

2) If the 240v is also used to supply consumers, it is best left with the ground relay enabled in the inverter, in which case, all of the 'neutral' outputs from the auto transformers will be ~120V with respect to ground / PE. If this is likely to cause a hazard, then an isolating transformer should be used rather than an auto-transformer.


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alaskannoob avatar image alaskannoob Mike Dorsett commented ·

We are planning on using the 230V for several 230V appliances, and splitting it into 110 for outlets that way as well.


We haven't figured out how we're going to ground the system yet. We're off grid, so I think we have options. I just don't know anything about it yet.

You wrote, "If this is likely to cause a hazard, then an isolating transformer should be used rather than an auto-transformer." How would we know if it would be likely to cause a hazard?

I am planning on adding to the 700' trench a 10 AWG cable to connect the inverter to the Ground Relay of the AT. I am guessing this will work, I can't find any info on how much voltage/amperage is required to the relay for it to function properly but the printed manual that came with it says it's a 12V signal sent from the inverter. I would imagine even with the voltage drop that would probably work, I don't know. I suppose I can test that before I fill in the trench and just get a different wire worst case.


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