Backup load (LD) and bypass
Hello,
I am trying to understand how the circuit that feeds the backup load (LD) (aka essential load) on the Sunsynk hybrid units works.
Let's assume that I do have a grid connection, PV and a battery, and that I have only essential loads (LD) connected and no HM (home) non-essential loads. Also, no export to the grid is needed.
Question: in normal circumstances, when the grid is up and stable, the sun is present and/or the battery is charged, is LD sitting "behind" the inverter and exclusively fed by its output, or is it exposed to the grid (same as HM would be if I had a HM load)?
Another way of asking this question is to use an analogy with UPS units (see link below): does the Sunsynk unit act similarly to an online UPS or similarly to an offline UPS (or maybe to a line-interactive UPS) with respect to LD?
Or does that maybe depend on which mode is used? Could it be that the unit acts like an online UPS in "zero export + limit to LD" mode and as an offline UPS in "zero export / not limited to LD" mode? Note: in the older firmware, this would be "LD first & zero export" mode and "HM first & zero export" mode.
Once that question is answered, I will have follow-up questions.
Explanation of what "online UPS, offline UPS and line-interactive UPS" are: https://community.fs.com/blog/line-interactive-vs-online-vs-offline-ups.html
1. The essential loads work like this. According to your setup this can be different, but normally your load will be first supply by PV, then if that is not enough from the battery and if the Essential load exceeds the PV and battery power the shortfall will be taken from the grid. So this will then classify it as an interactive power source I think as in this case you actually have 3 sources.
2. If you install only a battery and inverter for backup purposes and the setup is set accordingly the power will always be taken directly from the grid, only the moment the grid falls away the inverter will take over the load and when grid is restored it will load the batteries and wait for the next power failure.
In both cases 1 and 2 the inverter will however monitor the frequency and the voltage to see whether they are out of limits. These limits can be setup in the Grid Setup(Grid Vol High/Low and Grid Hz High/Low). So the moment either the voltage or the frequency go out of these parameters the Inverter will disconnect the grid and take over and will continuously monitor the grid and only switch back when the grid is stable again. So I guess the inverter is inter active in this case. I hope this give you a better idea of the working of the inverter.