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Blog - LiFePO4
FAQ: Connecting battery packs into a single battery bank
Question: I have an „old“ 48V pack made of 16 cells. I wish to add more cells. Can I connect another pack of 16 „new“ cells in parallel to the „old“ pack?
Answer: We do not recommend connecting „old and new“ packs together. Please read this centuries-old wisdom: 16 Nobody sews a patch of un-shrunk cloth upon an old outer garment; for its full strength would pull from the outer garment and the tear would become worse. 17 Neither do people put new wine into old wineskins; but if they do, then the wineskins burst and the wine spills out and the wineskins are ruined. (Matthew 9:16, 17)
We certainly do not recommend connecting two „strings“ together at the high DC level. The LiFePO4 cells have very small internal resistance and connecting cells at high level voltage (e.g. one pack is 53V, the other pack is just 48V) will cause extreme currents that may cause damage to the cells. Also the operation and the performance of the two „string connected“ packs is quite hazardous.
The only option is connecting the cells (of the same capacity) at the single cell level. However for the connection at the cell level the cells should be of the same type, model and capacity. See details here.
Also for the BMS: you still need just one BMS for a pack that will be made of the single cell level interconnected cells.
