AC Coupling of Radian

Discussion about adding energy storage to grid-dependent inverters using OutBack Power technology
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AC Coupling of Radian

Post by bobnden »

I have a Xantrex SW 5548 that I plan on AC coupling to an Outback Radian GS8048A-01. The Xantrex is fed by my solar array No. 1 (2kw, 48v), through an Epever Tracer charge controller (80A, 48v).

The Outback will be fed by my other 2 solar arrays No.s 2 and 3 (each 3kw, 48v), through a pair of Outback MX 60's (60A and 48v each), and monitored by a Mate 3.

I have 2 independent LiFePO4 battery banks from 2 different manufacturers, both of which are 48v w/BMS, wired independently in parallel, with similar charging specs from each of the manufacturers.

One is a 3-battery bank, (30kwh), which I intend to connect directly with the Outback inverter, while the other is a 2-battery bank (10kwh), which I intend to connect directly to the Xantrex.

I've been led to believe that one should not parallel-connect batteries from 2 different manufacturers, hence the separate wiring scheme for each battery bank to each inverter, with no interaction between the battery banks.

Will this setup have any negative impact on the Outback's AC coupling operation, by having 2 separate battery banks?

If so, should I ignore the warnings, and wire both banks together in parallel to the Outback, such that the Outback sees only one huge battery bank that is fed by 3 solar arrays with a separate charge controller on each array to the common battery bank?
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Re: AC Coupling of Radian

Post by raysun »

...a Xantrex SW 5548 that I plan on AC coupling to an Outback Radian GS8048A-01
How is it envisioned that the two inverters would be "AC coupled"?

I'm not an AC coupled inverter expert by any stretch of the imagination, but I do not believe the outputs from the Xantrex and the Radian can be coupled in any safe manner.

The GS series inverters are 240V split phase units, and can be AC coupled to specialty inverters that are designed to be directly grid-tied. The common denominator here is both are 240V split phase and both are synced to the grid frequency. No grid to sync with and I believe the string inverters generally shut down.

Were the two inverters to drift out of phase sufficiently, internal circuit damage could result.

The 120V single phase Xantrex couldn't, of its own accord, match the 240V split phase Radian. I fear if "AC coupled" means tying their respective outputs together, there would be catastrophic failure in one or both units.

Its correct that the two dissimilar batteries can not be combined in parallel as a single unit. The lower capacity battery would surely experience premature failure without extraordinary and impractical precautions. It will be best keeping them associated with their respective inverters and charged independently.

That raises a question. The Xantrex is a trusty, but old war horse. Is it even compatible with the charging and voltage requirements of modern lithium batteries? Hopefully so.

IMO, the bottom line here is these are two independent battery-based inverter systems with solar charging. Its best they remain independent, servicing their own loads, while in operation.
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Re: AC Coupling of Radian

Post by sbrownian » ... p-163.html

"The SW Plus is not designed to sell power back to the grid."

So, it might not sync well, which could let out the magic smoke at the most inappropriate time possible...
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Re: AC Coupling of Radian

Post by bobnden »

Aha. I now see the error in my thinking of AC coupling the single phase120v Xantrex to the 240v split phase Outback. Thank you for pointing that out.

So... on to your recommended Plan B:
I keep both systems independent, and DC couple each to the grid separately. This should be viable, as the Xantrex has an after-market Xantrex GTI interface as well.
I'm just no so sure that the Xantrex GTI meets the latest, greatest updated California GTI standards. If not, it goes on Ebay, and I find another.

As far as using the LFP batteries with the Xantrex, they have a recommended charge voltage of 56.4v, so I should be able to set that in both the inverter and the charge controller from what I've seen.
The recommendations I've seen elsewhere is to simply set the EQ to Zero for Lithium-based batteries.
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