# BMS/Charge Controller Question

Unsure if this is the right area to ask. I’m very new to 18650’s.

I have a portable battery bank that uses an IP5568 (link to spec sheet) to manage charging of devices as well as act as a BMS for up to 16, 18650’s in parallel.

I plan to pair the battery bank with 16 brand new 18650’s (2600 to 3200 maH range) that will go through an initial run through an analyzing charger of some sort to ensure similar capacity, charged voltage and IR reading.

The 5568 spec sheet states “”…when the battery voltage is higher than 3V, enters constant current charging stage, the maximum charging current at battery port is 5.0A" on page 11.

Would I be correct in stating that I need to maintain at least 5 cells in the battery bank to ensure that the 5A the IP5568 could potentially put out lands inside the .5C charge rate that the cells are expecting?

If the maximum output for the battery bank is 18w @ 5v I need cells that can at a minimum handle 3A constant discharge, but ideally more for safety margin - is this correct?

Thanks

Thanks for joining the gang, Cardnyl!

That is incorrect.

“.5C” means half the capacity rating. If you’ve got a 2700mAh cell, .5C is 1350mA.

5.0A / 5 = 1.00A per cell. This is .37C of 2700mAh.
5.0A / 4 = 1.25A. This is .46C.
5.0A / 3 = 1.67A. This is .62C.
5.0A / 2 = 2.50A. This is .93C.

You’d be fine with as few as two cells to stay under a 1C charge rate, but three cells is closer to .5C.
A charge rate of .5C is generally recommended for longevity, but a lot of cells are rated for a charge rate of up to 1C, and some are rated for 2C or even 3C maximum charge rates, such as Molicel P30B. Using a P30B, you could use just one cell, and it should handle the 1.67C charge rate just fine without getting too hot.

2 Thanks

Thank you for taking time out to reply. I screwed up the math before posting.