Understood, if you have a large number of cells in a box that you can't open. Balancing is a very good idea.
However, is it fair to say that sometimes the need or degree of balancing can lead to a band aid approach?
My situation is a DIY project.
I have watched some DIY battery building where thin, nickel buses are happily spot welded by hand, to the cells and there was a lot of cells, a lot. They could not use aluminum or copper on account the welder was not hot enough but given a powerful enough welder I think I saw some success with copper. Cost wise there is a wide range of small spot welders in the market but it's not wise to skimp.
Given the number of welds I can probably say that overall the quality of the welds will not be consistent. If the welds are not exactly the same distance apart there will be lack of continuity. Miner and perhaps not so minor factors over time. There was also talk about cell temperature and cell swelling, which perhaps is more of a design problem. Like so many things in today's world maybe there is a certain amount of hype concerning BMS that needs to be considered.
My situation will be a bit different, I won't be welding. I will be screwing aluminum busses to the cells and I am using the mill to drill the 10 mm holes center to center in the 1/8th inch busses. Also the cells have a 22AH capacity so there aren't so many and each cell will be open to check .
I downloaded an open source 3D cad program, which is very helpful to see how a certain run of cells will look and how they can be bussed and connect to other runs.
Over time I will most likely use balancing but when I do I want to know what and why but within reason. Perhaps some times it is simply a need to clean up a connection to bring the cell back into sync.
Recently I have been looking at a old computer power supply to aid in balancing these cells. Two of the various voltages available are 3.3 and 5 volts The states on them indicate a fairly high amp but not so much, I found if you let them output full amps they will blow. Perhaps Five volts with variable resistance can be a way to balance?
If I use the formula above, (22 / 2 * .1) I get a BMS charge current of 1.1 amp. That seems high to me and like Bruce said shouldn't it be related to the time and charge rate of your LifePo charger? This little so called LifePo charger I have puts out a steady four amps for the entire duration (several hours) of it's charge cycle and powers down at 13.8 or so voltage. The cells seem to like it, there is still 12.8 or so volts left after a test. You can't compare lead acid to LifePo.
I have been spending a lot of time looking at inverters. There is some pretty fancy stuff out there. The surge in lithium cells has apparently caught some of the older inverters off guard, but most are now making room for lithium including BMS capability but the advised conditions for lithium varies from inverter to inverter. Usually there is (some times vague) user settings available to set the inverter to your Lithium not necessarily LifePo battery and not necessarily over/under cutoffs appropriate to the batteries . There will be a lot of note taking before a proper inverter pops up.
Off shore companies are turning out inverters, it's a buyer beware situation.
As I recall both Bruce and Ade are off grid I appreciate your feedback on inverters and other.
