Solar project thoughts.
Hi guys. Midway through installing. I have the panels mounted and working through wiring. Looking for thoughtful comments. Here are a couple pics of install to date.
Forum Discussion
HMS Beagle wrote:
I understand you will not be using a BMS routinely. How often do you think you will need to check the cell voltage, and how often rebalance?
I will check often at first. From what I have read from people using these batteries for some time now I can't find anyone yet that has needed to rebalance unless they are adding cells to their system. Like any battery with multiple cells no two cells will be exactly "balanced" or equal. The important factor is that no cell is outside it's safe usage zone on both the high and low ends. Other than that concern lies with a cell failing and as it dies dragging other cells along with it. On this issue again I haven't found anyone who has experienced this. One long time electric car conversion company who uses these stated they have never seen a cell fail.
When assembled in P/S configuration the voltage in the parallel wired cells are balanced or maybe a better term averaged along the parallel stings. So having 2 batteries configured 3p/4s I will simply be checking the 3 in parallel 4 times per battery to see if the grouped cells voltage is similar to the others. This is all a BMS would be doing as far as monitoring. To monitor cells at an individual level they need to be run in series and a separate BMS required for each string in series. I would need 6 BMS to achieve complete cell level monitoring/balancing. In the configuration I am running the BMS would be monitoring/balancing each parallel string in series, so I would need 2 BMS.
A problem with BMS systems I have seen is their fairly limited shunting capacity. One I studied maxed to 1 amp shunting ability per "cell". Not sure how that would help control a cell being charged at 2-3x that amount, not to mention 3 cells in parallel.
At least for now my solution is to keep charging and discharging levels far away from the cause of all failures I can find to date, over and under voltages. Fortunately some quality chargers and inverters are fully programmable to control charging and discharging cut-offs with exact voltage levels.
There has been much interesting reading chasing this project for a while. The only thing I am sure about is there is much more to learn.
