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I have a project that is powered with a 1s battery pack (multiple 18650 in parallel).

I use following module to protect against overcharge/overdischarge : https://aliexpress.com/item/32982853134.html Let's call it my "BMS", eventhough this does not balance anything since my battery pack is 1s1p right now (and become 1s6p later once tests are ok)

The reason I chose this module over the famous TP4056 is because I also use my project to charge some peripherals (earbuds, etc) which draw more than 1A (the TP4056 has overcurrent protection at 1A maximum). I have a DC boost that converts the 2.5V/4.2V of my battery pack to constant 5V output (and can output up to 3A, which is nice).

Here is my problem : my BMS does not limit INPUT current. I choosed this BMS specifically because it has big OUTPUT current (about 15A).

The datasheet of my 18650 cell says I can charge it at 1.7A max. So I need a way to limit the INPUT current to 1.7A today, but 10.2A later (6*1.7A, because of 1s6p). How can I do this?

For now, I am using my bench PSU to charge the battery pack, where I set it at 4.2V output and current controlled at 1.5A max. This is not very convenient. I later want to use my phone's usb charger, that can output up to 60W. But right now that would probably not end very well since it will output 12A (5V*12A=60W) into my 18650 cell (1s1p).

I will provide a hand drawn schematic if necessary.

TL;DR : How to charge 18650 Li-ion with controlled current?

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    \$\begingroup\$ You should probably ask this at eletrical stackexchange. Your question is not about Arduino and would fit better there \$\endgroup\$
    – chrisl
    May 17, 2022 at 22:52
  • \$\begingroup\$ I really do not recommend charging LiIon cells with a bench supply. Use a proper Lithium Ion charge controller (which is not the same as a BMS) to control the charge procedure. You might very well already have severely limited the life of your LiIon cells by using a bench supply, unless you know exactly what you're doing. Your phone's USB charger is NOT A CHARGER, it's just a power supply. You can't connect it to your cells directly. \$\endgroup\$
    – StarCat
    May 18, 2022 at 9:42

1 Answer 1

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A BMS is not a charger. It is a device that protects the pack from overcurrent, overvoltage/overcharge, undervoltage/overdischarge, overtemperature/undertemperature, and similar conditions.

Your phone USB adapter is not a charger either. The USB adapter is a power supply. It cannot be used to charge a battery without a battery charger between power supply and battey. And if it is an USB adapter, it is highly unlikely it can output 12A at 5V.

The TP4056 however is a charger. It can charge a single cell with up to 1A.

BMS and charger are two completely separate contexts, however, the BMS can be often integrated to the battery pack/cell or to the charging circuit.

Also, don't use bench power supply for lithium charging. It is not intended for charging, as it won't terminate charging when battery is full. Lithium batteries get damaged easily under wrong conditions, and damaged batteries are at a risk of bursting into flames or exploding.

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  • \$\begingroup\$ "Also, don't use bench power supply for lithium charging. It is not intended for charging, as it won't terminate charging when battery is full." - it's OK if you watch it and disconnect the battery when current drops, or charge to a lower voltage (eg. 4.1V) so it can 'float' safely. \$\endgroup\$ May 19, 2022 at 16:30
  • \$\begingroup\$ This does not answer my question. It's OK to charge with a bench PSU as I set it at 1.5A CC and 4.2V CV. The USB adapter is a GaN "charger" with Power Delivery. I can set it to output up to 20V if I negociate it accordingly with the data pins. I can then have the buck output 5V at 12A if I wish. \$\endgroup\$
    – Musa
    May 19, 2022 at 21:53
  • \$\begingroup\$ @Musa But it does answer your question. You need a lithium battery charging circuit between the battery and USB adapter. It will take power from the supply and charge the battery with CC/CV profile how lithiums need to be charged. \$\endgroup\$
    – Justme
    May 19, 2022 at 22:15

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