In the AC300 user manual it is “forbidden” to charge either AC300 unit via included wall charger while in Split Phase mode (big bold lettering on page 34). While the Fusion Box Pro is attached. You must buy the optional Fusion AC Input Cable.
So, my question is, Can I charge using solar panels while the Fusion Box Pro is attached??
I have the same setup (see my other posts), and the AC300 instructions are not clear (I plan to write up a new version later). The warning in the manual is that you cannot safely charge both AC300/EB500 and B300 setups on the same line (single phase) when using the Fusion Box Pro. The correct way is to either plug the supplied 120 VAC plug cable and Aviation Connector (for each AC300) in two separated outlets that are on the opposite phase halves (L1 and L2), or use a special (unavailable from Bluetti) Fusion AC Input Cable to supply 240 VAC L14-30P to two different Aviation Connectors , assigning L1 to the Master AC300 and L2 to the Slave AC300. I have installed a new 240 VAC L14-30R outlet with a 40 A circuit breaker near my setup (planning for that special cable), and instead use a special splitter (from my Firman generator) that divides the L14-30P to two outlet boxes to charge the two AC300 with their original 120 VAC cables. But if Bluetti will not supply that special cable, I will build my own, ordering the two 3-pin 30 A Aviation Connectors from Amazon, and the rest of the materials from a local hardware store such as Home Depot or Lowe’s.
As for solar charging, yes you can use up to two sets of panels on each AC300 even if they are attached to the Fusion Box Pro because they are DC inputs that do not affect the AC output. So go ahead and be successful.
I forgot to add that the B300 batteries can accept DC power independently from the AC300 so you can have two series in the AC300 and one in the B300 at the same time. The only drawback is that the AC300 does not monitor the power input in the B300. But it allows faster charging.