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I have 8 cells (samsung icr18650-26f), and I want to build a battery pack 4s 14.8v (4x3.7v) to power an LCD Controller Board that requires a 12v4amp input

I have an idea of the design of this battery pack, but I'm not sure

I would also like to know if a 4s2p battery pack could do this?

Or this

I'm thinking of using this bms https://es.aliexpress.com/item/4-strings-of-lithium-battery-protection-board-30A-high-current-four-strings-without-activation-of-automatic/32764959684.html or this https://es.aliexpress.com/store/product/4A-5A-PCB-BMS-Protection-Board-for-4-Packs-18650-Li-ion-lithium-Battery-Cell-4S/3100001_32827571864.html

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Your second drawing would be OK for 4s2p connection.

Second BMS has maximum current better suited for your application. The one with 30A limit won't provide necessary protection.

Couple warnings:

  • If you want to charge battery pack with output regulator connected then better option would be to use embedded charger with power path technology. Regular charger cannot tell the difference between current consumed by the load and current charging the battery.

  • If you OK with not using the output while charging then you can wire the input to the charging jack with internal switch. The idea is to disconnect output regulator when you plug in the charger.

  • before assembling your battery pack run each cell individually through charge/discharge cycle. Select only closely matched cells for your application. Then fully charge all cells again, let them cool down, measure voltage and connect parallel pairs only with identical voltage. After that you can connect pairs into 4S string and attach BMS.

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