i'm trying to charge a 5Ah single cell li-ion battery using bq24090 charger controller (up to 1A fast charge current) in parallel with a current boosting circuit. Overall controller should supply fast charge current at 0.5C rate(2.5A), theoretically. Which idea does make sense if i try to charge 4 of these li-ion batteries?

option 1: using 4 distinct charger controller as described for each one of the batteries

option 2: using single more advanced charger controller such as bq24600 (up to 10A fast charge current) and supplying 4 parallel batteries from that single output of the controller.

Thank you.


bq24090 http://www.ti.com/lit/ds/symlink/bq24090.pdf

bq24600 http://www.ti.com/lit/ds/symlink/bq24600.pdf


It's not a good idea to charge batteries in parallel, for any battery chemistry. If the batteries (cells) are in different states-of-charge, they may try to charge each other without any current-limiting between them. Better to charge them individually, so that the charger can sense each cell individually.

Cells that are permanently connected in parallel are usually assumed to all have the same state-of-charge.

  • \$\begingroup\$ Not really, you can use shunt resistors and FETs to bleed energy out of cells that reach the charge terminal voltage earlier than others. Obviously a bit of complex circuitry involved here, and each cell needs to be individually monitored, but it works. \$\endgroup\$
    – KyranF
    Nov 6 '14 at 13:33
  • \$\begingroup\$ Actually that may be for series connections only, my bad. I'm sure there is a way using diodes and FETs though. \$\endgroup\$
    – KyranF
    Nov 6 '14 at 13:36
  • \$\begingroup\$ Thanks for your responses. your answer leads to another question in my mind Mr.John. if state of charge of each batteries could be sensed through sense resistors and charge current is controlled by some switch mechanism through uP according to that state-of-charge, is it still not wise to charge batteries in parallel (just asking for brainstorming)? Thanks again \$\endgroup\$ Nov 6 '14 at 15:13
  • \$\begingroup\$ @vilacikovski Yes, if the charger can sense state-of-charge for individual cells, that's OK. But if the cells are truly in parallel (no intervening sense resistors, diodes, etc.) I don't think there's any way to know individual state-of-charge. I was thinking of cells that had been discharged individually and then connected in parallel solely for charging. \$\endgroup\$ Nov 6 '14 at 15:19
  • \$\begingroup\$ I think this is an acceptable answer. You do NOT want to charge in parallel. At minimum, if they are permanently connected in parallel, you would need to add a circuit protection device such as a PTC between individual cells. But that is an issue for the design of lithium battery packs, not about charging per-se. \$\endgroup\$
    – mkeith
    Nov 6 '14 at 19:03

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