Hi,
saptzae:
Parallel charging is the safer way one can charge an stack of critical cells. And itīs easy to design a highly reliable and dependable charger. There are some, IMO important benefits:
1) You fully respect the characteristics of each cell charging it with the proper current to attain the proper charge. Sensing itīs voltage and temperature during the charging allow us to improve the cell reliability keeping them bellow a safe specified temperature. (Remember the failure rate is correlated to temperature.)
2) You can even "help" a given cell to avoid to be transformed in a load (during heavy discharging) maintaining itīs within a safe voltage. (Something possible from energy of the DC bus itself). A dangerous polarity reversal would be practically impossible.
3) You can detect, register and inform on impending cell failures by a better characterization of the cell, instead of just doing this during the discharging. (Batteries for Av. application should have itīs recording capability)
Parallel charging would require one isolated inverter per cell, capable of the maximum fast charge current + associated heavy wiring. 4V 30-60A x 8. Please consider size, weight, connection, cooling and reliability.
All these factors were seriously considered and weighted before posting. IMO parallel charging is easily justifiable for an improved design.
Electrically, a parallel charge arrangement here would have 1/8th of the efficiency of the current 32V charge arrangement.
No problem with current high efficiency inverters.
Then, these eight chargers must be managed and monitored!
No problem!
Mac
PS
I am here trying to show a way to
increase the safety when using these dangerous cells. I yet adopted this approach in a (cost sensitive) design.
PS2
No thanks, KISS
I love the k.I.S.S. design approach.
When itīs possible. In this case every reasonable feature to save the reliable use of these dangerous cells are being considered. There are big advantages with Lithium batteries. Iīm trying to feel better and more confident when relying (if possible) on her.
PS3
The old approach of charging ("open loop") stacked cells directly from the bus in my mind is being seriously questioned. itīs too simple to be safe with dangerous cells.
PS4
To a better analysis of the 787 Batt/chrgr issue (thread focus) we would go beyond block diagrams (boxes) and must look to schematic diagrams (wiring, etc.)