Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,041
Each Sunny Island just makes one 120V phase. Each can pass through up to 56A to its phase, or supply something less inverting from battery.
With 2x SI wires 2s, you get 120/240V split-phase.
Sunny Boy is 240V. Say it delivers 20A (4800W), and you have 4800W load all one phase 1. Half that load is driven by SB (although SB doesn't put any current into neutral, connection may be optional); SB puts 20A into phase 1 and 20A into phase 2.
No loads on phase 2, so the SI on phase 2 sucks down 20A, 2400W to 48V.
On phase 1, loads are 4800W but only 2400W, 20A, coming from SB (on phase 1), so SI on phase 1 draws from 48V and delivers another 2400W, 20A on phase 1.
That behavior is similar to what an auto-transformer would do.
You might get a benefit from connecting an auto-transformer. It would try to balance load on the two phases, and Sunny Island would also try to balance. I don't know how much each would do.
There may be a problem having auto-transformer connected while on-grid. If grid is imbalanced and you receive different load on phase 1 vs. phase 2, the autotransformer would try to balance the grid.
I don't know if SI has an on/off grid signal. I've thought about that for my system.
An isolation transformer, 240V in, 120/240V split-phase out, would perfectly balance loads. It comes at an efficiency cost.
With 2x SI wires 2s, you get 120/240V split-phase.
Sunny Boy is 240V. Say it delivers 20A (4800W), and you have 4800W load all one phase 1. Half that load is driven by SB (although SB doesn't put any current into neutral, connection may be optional); SB puts 20A into phase 1 and 20A into phase 2.
No loads on phase 2, so the SI on phase 2 sucks down 20A, 2400W to 48V.
On phase 1, loads are 4800W but only 2400W, 20A, coming from SB (on phase 1), so SI on phase 1 draws from 48V and delivers another 2400W, 20A on phase 1.
That behavior is similar to what an auto-transformer would do.
You might get a benefit from connecting an auto-transformer. It would try to balance load on the two phases, and Sunny Island would also try to balance. I don't know how much each would do.
There may be a problem having auto-transformer connected while on-grid. If grid is imbalanced and you receive different load on phase 1 vs. phase 2, the autotransformer would try to balance the grid.
I don't know if SI has an on/off grid signal. I've thought about that for my system.
An isolation transformer, 240V in, 120/240V split-phase out, would perfectly balance loads. It comes at an efficiency cost.