BMS with charging current limit

[horvat.kamca]

Hi,
since off the shelf BMS don't limit charging current, I've designed simple circuit, that adds such feature.

Current limiting part is taken from https://www.instructables.com/Adding-a-Current-Limit-Feature-to-a-BuckBoost-Conv/. MINI-360 (based on MP2307) has fairly high idle current, about 3mA, therefore I've added low power voltage comparator and p-channel mosfet in front of MINI-360.

I'd appreciate any suggestions/improvements regarding my circuit.

Is it safe to use TS393 with 16V max voltage, or should I opt for TS391 with 36V max voltage? 12V adapter is used to charge the battery.

[beanflying]

Charging Lithium batteries is best NOT done at constant current alone and BMS boards are NOT a good way to terminate that charge they are a safety device. The TP 4056 is a good all in one multislope charger https://dlnmh9ip6v2uc.cloudfront.net/datasheets/Prototyping/TP4056.pdf

Have a read in this thread from a few days ago for some more links and chat. https://www.eevblog.com/forum/beginners/connecting-six-protected-18650-cells-3s2p-for-close-to-12v/msg3539256/#msg3539256

Will have a look at your circuit later but have a bit of a read your end too 

[tunk]

This is a 2S setup, so I don't think a TP4056 would work.
You could look at something like this:
https://www.ebay.com/itm/1S-2S-3-7V-7-4V-Lithium-Li-ion-Lipo-18650-Battery-Charger-Board-Charging-Module/383760467132?_trkparms=ispr%3D1&hash=item5959e804bc:g:6x0AAOSwfDhZgxLf&amdata=enc%3AAQAFAAACcBaobrjLl8XobRIiIML1V4Imu%252Fn%252BzU5L90Z278x5ickkxFtV7J5P58ubuVigtBH%252FexWUJJulHFOZONvhsmi7NeaWptZfIm%252F6vRGytBrs5zdKMM%252BaLol4prezO1o20FULwPTsd5weIspm%252B9iF8IXJ%252BK1kVgc2OBORw0pIC8cAiS%252BJI724KqCdmGrnC%252BUIHyIm3RwuTMKmQDrP1nzZEr07pweqXFIljhc5b6Zv8Un79kop%252B5aumeMMnIuCKk%252BaOpp%252FbsgVRMppGizG3dYOopOLgLlBiXscBgjv1%252FL3dXPe9PKsN%252BT4Dqxh47U3o8TrzRDrWXD3uBNpRXFP%252FFAIZdAsjZIoZ9AdcB6HvS6Gte5uVHEtGcFIHC6zHmSLoaHJFZI332GZ48Xxfjfot%252F134mtCfpAmOHw6Fb4EjrwcvAniRmNkRUY71JPhzR1m3h5KBlBub9WM6Yti7ZXJPctmQO4alcqCgKg08FM5uMS94v70vSI8rGlm8WkTu6i%252BgDTu9uSP1vvsGyCXT1o5sifR0fhsmvkN3e8xvCvCFaBJ2IxW%252BgwKID4cBfdY2i6f2%252BdFaQhsU76D4eJwV%252FjcUwxD0uz7FvZNBkUfQUwITnWofnA4to1PPI2fEuTAYhRZCgJyfF2VheQd3LnXlmqG9VkhuTphFUvyDx1%252BshGwruhQS6YmoNOX6IlgkKjbkzGherk30DmBmA1WpPhPcEVcvXofX77iGbRki8SpmhwoTe4KGaAeUI25akspqEsN5Mcf9RHCIj%252BFkju7wZQeuMl%252BDJOs9oDtcM3pQFLWvpOQTlZGVHMCX2e2lIky15OrElnVJTSphJBrRg%253D%253D%7Ccksum%3A3837604671326ede3d8a1044418496bfaadc9948fb16%7Campid%3APL_CLK%7Cclp%3A2334524

[beanflying]

I have done a workaround in the past for a play with some of the little Mornsun 0505S supplies https://www.mornsun-power.com/html/pdf/B0505S-1WR3.html to isolate the TP4056's. Just a different way to go not really the best but it allows charging multicell packs on a 5V supply as all the 4056's are isolated by the supply.

That board you linked also doesn't balance the batteries it treats them as a single nominal 8.4V cell so if one of them is low on capacity it will possibly overcharge and let the smoke out it will certainly trigger the BMS if fitted in that case. Proper balancing charge chips do exist that manage each cell of a multicell pack.

[horvat.kamca]

beanflying> Using 2xTP4056 with two isolated DC-DC converters seems a little too complicated for my project.
Thanks for noticing missing balancing feature of BMS, I'll slap on balancing board (https://www.ebay.com/itm/4S-16-8V-Li-ion-Lithium-18650-Battery-balance-Board-BMS-Charger-Balance-Circuit/383851475216)

tunk> 2S charging module looks like exactly what I need.

Also, there is an error in my circuit, drain and source of Q1 should be switched

[beanflying]

Not that complicated really  https://www.eevblog.com/forum/projects/multi-cell-lithium-charger-from-a-single-5v-supply/msg1454259/#msg1454259

Working fine since.

[mikerj]

Hi,
since off the shelf BMS don't limit charging current,

It is the job of the charger to limit charging current, NOT the BMS.  BMS is for safety; to detect overcharge or uderdischarge and sometimes cell imbalance.

[horvat.kamca]

I've realized my circuit is completely wrong, because voltages on input of opamp are outside of common-mode voltage range.

The purpose of opamp and mosfet is to turn on power to charging circuit only when 12V DC power supply is connected.

The circuit can be in two states
 - powered from 12V, then charging should be turned on,
 - powered from 2S battery (7V-8.4V), charging should be turned off

Can you point me to the proper way of doing this?