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jdw avatar image
jdw asked

SMA Sunny Island 6048 + Victron Autotransformer

Hi all,

Got a question for either a Victron tech or anyone who has experience with Victron Autotransformers.

I'm currently building an off-grid AC coupled system between a Sunny Island 6048 and a Sunny Boy 6000US. The Sunny Island is 120V ~48A max continuous output and the Sunny Boy is 240V 25A max continuous output.

In this AC Coupled configuration, which Autotransformer would be the correct choice here? During the first part of the day, I'm looking at around 48-50A on the 120V L1 leg as the Sunny Island is charging the batteries provided by the 25A 240V from the Sunny Boy.

Midnite's 6000W Autotransformer manual has this diagram:

Is a similar configuration achievable with either the 32A or 100A autotransformer?

My intuition based on current flow in autotransformers is that either one would work fine however I could be wrong. Still coming up to speed on how to do the calculations.

Thanks in advance for any insight.

Autotransformer
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1 Answer
ben avatar image
ben answered ·

I'm not familiar with all of those products, but I do know the various ways you can wire up the autotransformer. Maybe I can state some assumptions about what happens in the morning, when the sun comes up, and then try to answer your question:

1) You have a PV array and your "SB6000US" takes that and outputs 240VAC at up to 25A.

2) You have a battery that will be charged by an "SI6048." It takes 120VAC in and can charge at roughly 6kW.

Ignoring any other power flows that happen at other points in your day and night, you cannot use a single Victron AT to do this.

The Victron AT can source or sink a maximum of 32A on the neutral for 30 minutes, or 28A continuously at 100F. The neutral is where you will tap off your 120V feed to your charger.

Basically, a single Victron AT is good for stepping down or up about 3300KVA continuously.

You may be able to put two of them in parallel for double the capacity. Or you could find a larger, single transformer.

As a point of clarity, the 32A and 100A models are different only in the amount of current the 240V rail can handle. The toroid has the same transforming capacity in both models.

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