This is not a BQ24193 specific question but more of a general question I’d like to get help from the forum.
What I wish to achieve in the end is to create a circuit that can safetly manage charge/discharging of multiple(to be precise, two for the moment) Li-Po batteries in parallel. I want it to be commercial-grade safe.
The two Li-Po batteries have the same capacity and are both 1S. I originally thought combining the + and - nodes of the batteries and then attaching it to the charging IC(in this case, BQ24193) would be safe enough. (the below figure depicts what I planned to do)
Some google results support this method. Here are some of those:
https://learn.adafruit.com/multi-cell-lipo-charging/simple-balance-charger
http://www.electricrcaircraftguy.com/2013/01/parallel-charging-your-lipo-batteries_22.html
http://ww1.microchip.com/downloads/en/AppNotes/00231a.pdf
especially, the last reference seems to be the most ‘legit’ reference that I can find. Here’s the first paragraph of it that comments about parallel charging.
However, I have received comments from my friends that oppose this view.
According to a friend of mine who is researching battery management systems, says that charging two Li-Po batteries in parallel with one charging IC could lead to problems because of absence of ‘balancing’. The small difference between the two batteries will eventually widen enough after sufficient time where the two batteries will show different indivitual voltage levels. The wider this gap becomes, the more dangerous it is to connect the two batteries in parallel. To counter this problem, my friend suggested either
1) get a circuit that will do the ‘balancing’ or 2) attach a charging circuit for each battery.
for option 1), I have not been able to find a circuit that supports balancing for parallel batteries. I hoped to find something that could allow me to build a circuit something as below.
for option 2), I guess this would be the ‘ultimately’ safe-ensured method but at the same time, I’m doubtful if this is the correct.
To conclude, I’d like to know what is the proper way to implement parallel charging with Li-Po batteries. Can I directly connect a pack of batteries to a single charging IC or adopt a more complex circuit? If so, what would I need to do?
I’d be grateful if users on this forum could provide their insight on this matter based on more reliable, professional expertise. Or, if you have had any experience building a power bank using Li-ion or Li-Po batteries, your comment would be much appreciated.
P.S. These are some tips regarding parallel charging of Li-Po batteries that I’ve gatherd from various google results. Listing them here just to avoid trivial comments.
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if multiple Li-Po batteries are to be connected in parallel, the batteries must have identical cell stacks. i.e., combine 1S with 1S. 2S with 2Ses only.
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Parallel connection of batteries that have output voltage difference more than a certain amount(0.1V is one value that I’ve seen) could cause problems. So for initial parallel connection, try to minimize this voltage gap.
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Assuming two batteries are connected in parallel and one of it dies(effective capacity becomes extremely low than described), charging/discharging this along with the other battery which is in a good state, could be dangerous.
* this third statement is what I’m most afraid of. Is this really true? -
The maximum charging current should match to the lowest charging C-rate among the batteries.