docnjoj wrote:A good BMS like Cellmans or Pings or the European one agniusm is using will work with a good charger.
Do I understand correctly that a BMS can somehow "disconnect" a cell within a pack if that cell's voltage goes too low during discharge (load)? If so, how does it do this? I thought there was a single wire tied to the top ( +) of each cell that ran to the bms and allows the bms to sink some current in order to drain a cell down a bit during charging in order to balance cells. That makes sense to me, but I read somewhere that it can also keep a low cell from being drawn down during discharge and I don't see how that is possible with only a small wire that can only handle 2-3A...
We have to understand there are a lot of approaches to doing "battery management," many different devices that can be applied. Of course if there is a computer chip and programming in the circuitry, then the management has been delegated. The other approach, the one I'm using for now is to use the power of my own brain. Doing so requires good information. Hence, my choice is to introduce the "Watt's Up" meter:
"Watt's Up" & "Doc Wattson" Watt Meter and Power Analyzer User's Manual. RC Electronics, Inc.
10.5 Balancing Battery Pack Cells. You don't want battery pack cells going below their minimum safe voltages for safety and battery life reasons. A battery pack whose individual cells are all balanced delivers the most energy since all cells are exhausted at the same minimum voltage. If any cell is "out of balance" it may reach the minimum safe voltage before the others and continued pack discharge will damage the cell.
Its the differential uptake of charge during the charging cycle that I feel warrants concern. The Watt's Up meter gives me ongoing real-time performance information, telling me when to turn the battery off during use. But it also tells me the charge status after a full charge. I can use this information to gauge the overall health of the battery. When I see degradation, I can then check each cell individually to see the different voltages of the cells. If there's a low one, I can then apply my 2 amp Voltphreaks charger to just that cell and bring it back up, if it wants to. If a cell persists in dangerously low voltage despite attempts to charge it, it time for replacement.
The beauty of Agniusm's kit, in part, is that it also makes deconstruction easy. That way the individual cells can be pulled out or reordered. I believe the placement of the cells in the pack may influence their relative charge/discharge, so simply changing the order of the cells may improve the battery's overall performance; swapping inside to outside, near the poles, for instance.
Its an ongoing experiment. For now, my pack holds charge beautifully, I have the data I need, and I require nothing more. This state may persist for years, before I need to intervene. I hope so.