I plan to build a 4S2P battery pack and have chosen to use a 30A BMS. My understanding is that the BMS will stop the individual cells from charging beyond 4.2V.

In such an environment, can I charge my battery pack using my 20V 4.5A laptop power adapter, or do I specifically need a 16.8V 1-2A charger?

The measured capacity of the cells are 1500 mAh or 3AH in the finished battery pack.


This is the BMS and charger I bought, respectively:



I am going to use two 4x18650 battery holders. I will connect the cells to the BMS as mentioned in the diagram and will connect the P+/P- to a 5.5x2.1mm female power jack.

I can then plug in my charger into that or plug in my motor or other electronics into that. Does this sound good?

  • \$\begingroup\$ Your BMS should have some kind of datasheet or manual with current and voltage ratings. \$\endgroup\$ – Dmitry Grigoryev Mar 16 '17 at 16:40
  • \$\begingroup\$ The ad says it's a protection board, not a charging circuit. You'll need a proper charger for that type of battery - or keep the Fire Brigade on speed dial. \$\endgroup\$ – Brian Drummond Mar 16 '17 at 21:15
  • \$\begingroup\$ No. You need a charger to charge your battery pack. You cannot charge lithium ion battery packs with fixed voltage supplies. You need CC/CV, and you need to detect end of charge, at which point the charging must cease. \$\endgroup\$ – mkeith Mar 16 '17 at 23:46
  • \$\begingroup\$ @mkeith and BrianDrummond Can you see the updated question and post as solution. \$\endgroup\$ – Shahid Thaika Mar 17 '17 at 6:36
  • \$\begingroup\$ You still need a charger. There are no detailed specifications listed for that power supply. It may or may not be a real charger. For example, does it have any method of detecting end of charge? Or does it float at 16.8V forever? How accurate is the 16.8V? I might suggest you go in a different direction. Instead of building a permanent pack, and charging as a pack, maybe you can use individual 18650 cells, and charge them with an off-the-shelf charger (for example, chargers made by NiteCore). \$\endgroup\$ – mkeith Mar 17 '17 at 6:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.