Hey guys, I have a dead battery pack I want to replace. It would be easy to just use the same BMS and same batteries, however I would like to modify it in 2 ways (1. increase capacity, 2. Make a powered plug in input capable of using the light and charge battery pack simultaneously).

Information: it's a 4s2p 18650 battery pack 14.4V, 4.8ah, (8 batteries total with 2400ma capacity each). See images.

The battery doesn't state the discharge rate (how many amps or C's). However the draw to the light when measured is between 4.5 and 5 amps (stated battery life is 1.3 hours for light).

Question 1: If I increase each battery capacity to 3500ma would that change the amperage to the light? Or would that not even matter since the light will only draw what is needed? and how would/does the BMS play a role in that or would a BMS not change the rate of draw from the light?

I have this battery in mind as a replacement https://www.imrbatteries.com/samsung-35e-18650-3500mah-10a-flat-top-battery/ (even though it states 3.6V, which is technically 14.4V in series vs 14.8v a 3.7v would have, would that voltage differential even make a difference?) Also do you guys think the 8A max continuous draw should be plenty safe margin for the required draw? Would a draw of any amp higher than required work?




I will move on to the plug in part later on as to not put too many questions and information. However I will state that the normal power supply DC output is 16.8V 2A max. I purchased a 16V 4A max power supply and bypassed the battery, directly to the circuit for the light, and ran the light for 10 hours stress test no problem.


Thanks in advance for your guys help,
Alex

 

Your load only draws what it needs, putting more cells in parallel increases the current drain, then you have the problem of charging them up, which takes longer.

The Bms pcb prevents over/under voltages for the cells when charging or discharging.

Any cells in series the battery is governed by the weakest cell.

 

Thanks for the reply Dodgy,

If the light pulls 4.5-5amps, would any battery with a 5+ continuous discharge rate be fine?

-Alex

 

If you're looking at 5aH rate, i would go for 7aH for safety.

 

Ok, so the 8A max continuous battery I mentioned above should be plenty safety margin? Just for information, even a 20A max continuous discharge rate would still work fine?


Now, if I get a 16.8V 5A power supply, to supply enough amps for the light and at the same time for charging battery pack, would the power supply push all 5A to the battery pack if the light is turned off? Would the BMS prevent that from occuring or would the power supply (if Constant voltage) prevent overcharging from occuring?

-Alex

 

The bms controls the battery charging not the psu.