I have a 5KW Multi with 5KW of AC coupled solar (oversized arrays, PV inverters rate limited as per the 1:1 rule) as well as a MPPT which on ideal days adds another 1KW of solar power, all connected to a 600Ah 48V Lead Carbon battery bank. I recently enabled DVCC with SVS and STS and a current limit. The BMV-702 now reports high voltages: 57.8V, which indeed is a bit too high for my liking. The Multi is set to: absorp: 55.0V, float: 53.70V, the MPPT 250/60 is set to absorp: 55.20V, float 53.90V.
Often I see that the MPPT 250/60 has completely derated itself, while the Multi is still pumping ~1KW into batteries that are full. I would expect to see the Multi derate itself first (due to the lower voltages programmed).
I have two questions:
1. What could cause a high voltage situation of almost 3V above the programmed absorp voltages? The only explanation I can come up with is that it's caused by as high load disconnecting while the batteries are full. If this is the case, would this be considered an issue? Note: I have only seen this happening after enabling DVCC and my theory doesn't seem to be supported by the graphs:
2. Why is the Multi not derating before the MPPT is derating?
When the batteries are full, I prefer to derate the large AC coupled arrays first, and leave it to the MPPT to keep the batteries floating. High loads will of course cause the Multi and thus AC coupled PV inverters to rate up again and once those high loads are disconnected, to derate again. When the batteries are full, this happens fairly quickly.