Hi
I’ve been using 2 x Victron MPPT 100/50 and a Multiplus II 24/3000 for a few years and it works well. It is controlled / monitored via a Cerbo GX. Power comes from 4 x 400w panels and 2 x 600w panels. All p-type half cut cells.
Previously I was charging a 24V 160Ah LFP battery which only had a Bluetooth BMS, so didn’t integrate with Victron.
I’ve recently purchased a DIY battery case with a JK 200amp BMS (PB2A16S20P), and some EVE LF280Kv3 cells. I originally ran it with 8 cells to match the old 24V LFP battery (which is now disconnected). This was to give me some experience of using a BMS with Victron and this seems to work fine and has been running for about 3 months.
I’m now looking to move to 48V since I want to grow the system, add more panels, and get a larger Inverter (2 x Multiplus II 48/5000), without the current levels going any higher (and the 48V equipment is cheaper).
I originally avoided 48V since I have a LOT of shade in the garden, due to 6 large trees, and so I’ve been running 3 strings of 2 panels each, to reduce the impact of panel shading affecting the other panels. But this means the PV voltage coming into each MPPT is about 60V (2 x 400w half cut panels per string), but in the winter / shade, this sometimes drops to the low 50 volts (perhaps for 10 minutes at a time) which is too low to charge a 51.2V LFP. Admittedly, the battery will charge when there is decent sunlight, but I wanted the system to continue to charge, even in the winter.
Since I have a DIY battery and the BMS handles anything from 8s to 16s, I thought I’d experiment with a 14 cell arrangement since that gives me a lot of additional “difference” between the PV voltage and the battery voltage (since the battery voltage is over 6V less when using 14s). I’ve setup a completely separate system for now, put 14 x EVE LF280Kv3 cells into a separate DIY battery, configured the BMS for 14s and purchased a Victron 150/45 MPPT to connect to some of my 400w panels (which I’ve switched over to the “new / experimental” system).
My existing Victron 100/50 MPPTs are setup as follows:
Absorption voltage: 28V = 3.5V per cell
Float voltage: 27V = 3.375V per cell
I picked these values because I felt that charging at 3.5V per cell would help increase battery life, by not charging too quickly and never going to 100%
I wasn’t too certain about the float voltage, I feel that maybe it could be set lower at 3.35V per cell. Not sure.
For the new 14s system, I simply took these values (per cell) and adapted to a 14 cell arrangement:
Absorption voltage: 49V = 3.5 * 14
Float voltage: 47.25V = 3.375 * 14
So far so good and it appears to work, although it is winter in the UK and so I’m getting some pretty terrible Kwh from the sun, so I need to run this longer to get a better idea of the reliability and if the battery continues to charge when the solar input is low.
I wanted to ask the community their opinion on this setup and the choices I’ve made. I’m aware that I’ve created a custom system and I’m pushing my knowledge of the topic. If I’m going to replace all my MPPTs with 150/45 (they are cheap), I could switch to using 3 panels per string (I couldn’t do that with the 100/50 since the PV voltage would be VERY close to the max at 3 x 32V) and then move to 16s on the DIY battery, but I think that the crazy shading in my garden will cause major problems if I have 3 panels in series. I’ll also have to buy more matching panels before I can have 3 panels per string).