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I am trying to build a 2s 7.4V solar charged lithium battery pack to power an arduino UNO and SIM900 GSM shield. I have a 12V, 10W solar panel, BMS protection board and a DC-DC CC CV buck converter like the one in the link below. Now I know that I can use the CC CV converter to control the output voltage (7.4V) and current to the battery.

Question: Is it necessary to use a BMS protection board to stop current flow to the battery once the battery is fully charged i.e. reaches the output voltage of the converter? Does a BMS protection board cut the current supply to the battery completely?

Please help me in understanding the a battery charge controler vs combination of DC-DC CC CV converter and BMS protection board.

https://www.ebay.com/itm/LM2596-DC-DC-Step-down-Adjustable-CC-CV-Power-Supply-Module-Converter-LED-driver/191673918658?hash=item2ca0a7e4c2:g:4H4AAOSwMmBVo4rQ&frcectupt=true

https://www.ebay.com/itm/2S-5A-BMS-Charger-PCB-Protection-Board-For-2-Packs-18650-Li-ion-lithium-Battery/153094998246?hash=item23a52c48e6:g:-PkAAOSwvjdZSKBX&frcectupt=true

Using CC CV converters to charge batteries

PWM lithium battery charge controller schematic

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  • \$\begingroup\$ Yes, lithium batteries need charge control. So, add a diagram to your question showing how you will put these components together, then people can answer. \$\endgroup\$ – Solar Mike Mar 18 at 6:47
  • \$\begingroup\$ The BMS is there as redundant protection in case the charge circuit fails. You should not rely on the BMS to perform normal charge functions. The difference between a CC/CV controller and a charger is that the charger detects when the battery is full, and then it disconnects (stops charging). A CC/CV controller maintains the CV voltage indefinitely after the battery is fully charged. Obviously in your case, since it is a solar setup, the CV voltage will be withdrawn at night. But I would still recommend that you use a charger IC rather than a CC/CV controller. \$\endgroup\$ – mkeith Mar 18 at 8:46
  • \$\begingroup\$ Thanks, I've uploaded two schematics. The first shows what I initially thought doing...using CC CV converters to limit the voltage to the batteries. But I guess it will keep pushing current into it. Is this really so bad for the batteries on such small applications? The second image shows my proposed configuration to charge lithium batteries from a solar panel, using PWM charge controller and then CC CV converter to bring down the voltage and current from 7.4V batteries to arduino and GPRS shield. I would appreciate your comments on the two configurations. Thanks \$\endgroup\$ – Reginald Barry Mar 20 at 2:54
  • \$\begingroup\$ To add to previous comments, what does this controller actually do banggood.com/… \$\endgroup\$ – Reginald Barry Mar 20 at 2:55
  • \$\begingroup\$ Long ago when they first started using Lithium Ion batteries, one of the first things they discovered was that holding them at constant voltage (4.2V per cell) led to failures. It is absolutely not a good idea to hold a fully charged Lithium ion battery at 4.2V (per cell). MAYBE it would be OK at 4.1V per cell, but as far as I know, no cell manufacturer will actually come out and say that it is OK. Chargers detect when battery acceptance drops below some threshold (such as 0.1C) and then drop the charge current to zero until the battery voltage drops below some threshold. \$\endgroup\$ – mkeith Mar 20 at 3:55

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