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happysteve 14th December 2016 01:40 PM

18650 battery management modules
Iím not sure if this is the right section for battery power supplies but here goes.

Iím looking to power a small boombox using several 18650 battery cells, probably about 5 or 6 in series depending on the exact voltage requirements (which I will find out later after testing various amp modules). I want to make a battery pack by connecting several batteries in series and using one of the cheap Chinese made BMS modules available on eBay to safely control charging, discharging and balance between the cells. I will then use a laptop style power adapter to charge the pack via and external socket on the boombox (nice and easy).

Batteries Iím thinking of using are Panasonic NCR18650B. Here are examples of the BMS modules I am looking at:

5S Lithium 18650 Li-ion Battery Packs BMS 18.5V 15A Protection PCB Circuit Board | eBay

6S BMS PCB Protection Board 22.2V Li-ion Lithium 18650 Battery 6 Cell 10A 25.2V | eBay

15A BMS Protection PCB Board For 5 Packs 18650 Li-ion Lithium Battery Cell 5S | eBay

Has anyone had any experience of using these type of BMS modules? Are they reliable?

basreflex 17th December 2016 10:12 AM

these BMS circuits consist of a per cell voltage detector that switches in a resistive load when the voltage exceeds 4.2V.
plus a circuit that limits the excessicve charge and discharge currents and adds undervoltage protection , probably only acting on one cell.

some precautions:
only use new identical cells of same make and lot.
the BMS does not function as a charge controller, and the laptop supplies are no real charge controllers, just supplies.
there not much difference between brands. they mostly use seiko or ricoh chips.

happysteve 17th December 2016 06:27 PM


Originally Posted by basreflex (
the BMS does not function as a charge controller, and the laptop supplies are no real charge controllers, just supplies.

What would I need to do to safley charge the battery pack?

happysteve 18th December 2016 06:46 PM

Maybe I should put a voltage regulator between the power supply and the BMS so that I can control the exact charge voltage going into the BMS and buffer it from any ripple or spikes from cheap power supplies?

Somthing like this maybe:

DC-DC Step-down Power Supply Constant Voltage Current Converter Regulator 6A 36V | eBay

Would that work?

AndrewT 19th December 2016 10:34 AM

If you are charging small batteries where the maximum charge current is around 500mA, then it is easy to transform, rectify and smooth the mains to an approximate DC.

Then add on a current limiter set to your maximum current for the battery. An lm317 does this very well for lower current chargers.

Follow that with a voltage regulator set to the maximum voltage of the charging battery. Again an lm317 does this.

This works well for lead/acid and Nicad.

For any of the modern technologies the above works, but needs add ons.
Temperature monitoring, individual cell voltage monitoring, timed charging after reach some set point.

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