T1 Terry wrote: ↑Tue Jun 27, 2017 1:31 pm
As I said previously, just because you don't see it doesn't mean it's not happening. You really don't know if you have a cell run away as the 14v cut off is reached, nor do you know if the cells actually reached fully charged because you don't see how far the voltage drops when the charging stops. As the graph shows, there are 2 cells way out of balance to the other 6, yet all are within 0.02v of each other at the 5 hr mark when the sun stopped creating much charge at all. The few steps after that would be inverter load from the fridge cycling and possibly Brian cooking dinner with the induction cook top, the inverter runs 24/7.
T1 Terry
That makes no logical sense at all, of course you will know if a cell is running away, by simply checking cell voltages and what you describe and along with your graph, may happen in your type of system, but not in mine and if my flux 117 can't ascertain the true voltage of a cell, how can you. Been down the road of switching relays and active/passive BMS many years ago and the associated frustration and never ending system watching. Now have a simple 2 component system, that does the job better than anything else we tried, is yet to fail and works extremely well.
If you don't have a good active energy transfer balancing system, of course you may spend your time trying to balance your cells. Previous balancing systems I've used bleed cells down, which doesn't really work and wastes energy, But a balancing system that moves energy from cell to cell, is not wasteful but efficient, as it doesn't effect anything or have loses and seems to smooth things out much better.
Switching on and off charge may slowly balance your cells, but using a constant balancing system you never have those problems unless you have a failing cell. It's the same with using a single stage bulk charge controller, compared to using a modified but still lead acid charger, L/A all have tapered charging and lifepo4 don't handle tapered charging very well when they are reaching their capacity. On the other hand lifepo4 handle full charge until full very well and seem to perform much better under those conditions.
There are no failed cells in any of my systems and after spending a couple of years constantly watching them many times a day, the charging system and regime works, 9 years is a pretty good time line for usage understanding. To me in my technical ignorance, switching on and off charge, even if it is rapid, replicates a lead acid charge regime, especially when you read they use 14.4v as the upper charge cutoff for lithium and float to that. That seems like they think every lithium cell is no different to lead acid and li-ion parameters are the standard, lifepo4 and other lithium chemistries, have different charge regimes and voltage capacities.
The first time I used this system, was very nervous and watched 300amp coming into my system thinking I may end up with a load of junk after this, much to my mates delight. When the chargers switch off and the pack settled, which took just a couple of minutes the cells all sat at 3.45v and the pack voltage 13.8v. Every day since it has been the same, when we get back from travelling the first thing I do is check all cell voltages and they are all balanced. You can't ask for better than that for an outcome.
I would have thought that they would had started more like they finished.
