Thanks for the input. I’ve attached an updated diagram with some equipment I purposefully left out to make things simpler.
The inverter is a pure-sine wave 1500w UL certified Go Power 24v and you are right, it will automatically shut off under certain conditions, one being low input voltage of 20v. The problem is that once off it wont turn back on with me having to manually cycle it. Hence my need for an automated solution.
As for the logic: I was actually thinking of using 3 variables: low_DC_voltage, high_DC_voltage, timer
So I figure that given the solar system is configured as primary source supplying a steady AC load on the AC transfer switch, in the event that over time the load draw depletes the battery array to the point that its voltage drops to 20v or less, the arduino will:
- Turn off the inverter, (causing the AC transfer switch to automatically fail-over to the secondary grid power source).
- Wait until the following condition are met before turning the inverter back on:
a. The DC battery voltage rises to say… 26v, AND
b. say…30 minutes have passed
- The inverter now back on will cause the AC transfer switch to automatically switch back to the primary solar power source
Yes this inverter is able to be turned on or off via the serial rs232 connection. Go power sells a simple cable remote with push button that toggles the inverter on/off, so I know it’s just a matter of shorting 2 of the 3 active pins in the 9-pin port. I’m still waiting to hear back from them which 2 pins to use so that I can wire the arduino relay accordingly.
As for the 24v 26v discrepancy, my mistake. I meant 26v although this might even be higher (like 28v).
I take the batteries off line every so often to desulfinate/charge them so I think they’re ok, but I really like your suggestion about monitoring things at the cell level. I just wouldn’t know how to do that at all
Also I have no idea what, in addition to the mega board and relays, I need to accomplish all this. I’ve seen some arduino voltage sensors on the internet but don’t know if they are purposed for this project. Plus there’s the whole thing about splitting the DC (24v) voltage down to under 5v so the arduino won’t blow up. Lastly the code, which I’d need some serious help with.
As for the question about the charge controller, yes it does have a load output, but it’s DC and limited to only a few amps and only on at certain times of the day/night (i think). The charge controller’s charging output is also DC but in a 24v DC system like mine will output as much as 1000W (assuming my solar panels can supply this which they cant as I have only two 225W panels in series).