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Newcomer here and a total noob. Ok so coming to the question i am planning to build a battery bank with 18650 cells. I am opting for a 3s4p configuration as its closer to my operational requirements. I want to install a 3s 10 amp bms board without balancing function. Also i shall install balancing leads in such a way that they can connect to 3 individual TP4056 boards with isolated power supplies. First using a constant current source connected to the bms power leads, i will charge the bank to approximately 12.0 volts. Then when the power supply cuts out i want to finish off the charging process throught the TP4056 modules with the goal of obtaining a balanced charge on all 3 cell groups. Will this work? Have i gone horribly wrong and i stand the risk of the whole contraption blowing up in my face? Kindly help!

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  • \$\begingroup\$ It works when new, but aging is not uniform and any imbalance can overcharge the weakest cell so that it accelerates aging on that cell. So a better balancer extends the life of the weakest cell. \$\endgroup\$ – Sunnyskyguy EE75 May 16 '18 at 19:31
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Using a switching power supply, and adding more batteries than you would otherwise need would keep the voltage from dropping much under heavier load. Also, if you have the option, using larger batteries (higher mAh), in series would be the best option without any doubt. This is a perfect instance where you would REALLY want to use a high efficiency Switch Mode Power Supply, (SMPS). This will give you over 90% efficiency, especially if made well. You will find parallel or series parallel configs very short lived, as batteries are notoriously unequal in voltage, especially under load.

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To begin with, batteries in parallel is almost always bad practice, for reasons I won't go into now. Go with series.

2nd: for even the most simple stuff, it is always best to include a schematic, and a detailed description of what you are trying to accomplish.

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  • \$\begingroup\$ Sorry for the lack of schematics. If i just put it in series, how would i get a higher current rating? \$\endgroup\$ – Chinmoy Sharma May 16 '18 at 19:48
  • \$\begingroup\$ If you are using a switching power supply, especially, adding more batterys than you would otherwise need would keep the voltage from dropping much under heavier load. \$\endgroup\$ – Sara Heart May 17 '18 at 0:57
  • \$\begingroup\$ Series has its own problems. If you have a lower capacity cell in series with a higher capacity cell, then the low capacity cell will discharge first. It will then have current pushed through it from the higher capacity cell. Bad when discussing nicad or nimh, catastrophic when discussing lithium cells. This can happen even with cells that have the same nominal rating. If one is older than the other, then its real capacity will be lower (effects from aging) and will run out sooner. \$\endgroup\$ – JRE May 17 '18 at 4:41

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