I just purchased this new Growatt Infinity 1300 SolGen/Power station. Problem is that Growatt doesn't provide an add-on external battery option. ?
So, I'm going to do a DIY add-on battery by connecting an external LFP battery bank to the Growatt's solar PV input. Of course, the Growatt won't be able to charge those external batteries, so my plan is to use an external MPPT SCC to charge the external battery bank, which in turn will charge the Growatt's internal battery when it's below 100% SOC, and of course charge the external battery bank until it also is at 100%. Fortunately, the Growatt supports a broad range in solar input voltage, from 12-100vdc, at a max 800W charge rate (see the Specs below).
Since the highest standard off-the-shelf LFP batteries are 48v (51.2vdc), I plan on using 48vdc LFP batteries in the external bank to minimize the current flow and reduce power losses and wire size to the Growatt. The external SCC would be putting out close to the 48vdc, which will feed the Growatt's input. I could use 24vdc, but 48vdc is efficient in transferring energy to the Growatt. Here's a simple diagram of what I have in mind...
I think the only tricky part is knowing at what voltage either the battery or the growatt will signal the SCC to stop charging. Since the Growatt's SCC will manage the charging of it's internal battery given a 48v nominal input and stop charging the internal battery at 100%, I figure it's the extternal battery bank's voltage that will trigger the external SCC to stop charging when the preset max charge voltage is reached.
So, have I missed anything here that will smoke something or cause me any problems?
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