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I've designed a BMS based on the HX-2S-JH20. The BMS design itself is clear to me, but as I want to use a 12 V DC plug for charging. The BMS takes 8.3..9 V, the circuit takes 5 V. I wasn't quite sure on how to hook this up.

I'm using 2 linear voltage regulators, both with a max input of 30 V. One outputs 9 V for the BMS to charge the cells, and the other takes the 9 V from voltage regulator 1 or the BMS and converts it to 5 V for the circuit to use (I hope :) )

Do you guys have any input on this? The part of the schematic I'm unsure about is boxed in red.

The 9 V is of course hooked up to ground, something I forgot to draw in the schematic.

Schematic

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    \$\begingroup\$ Where's your actual charging circuit? \$\endgroup\$
    – Finbarr
    Commented Aug 2 at 9:26
  • \$\begingroup\$ Damn, you are right, I kinda thought the BMS would handle that, but it doesn't include charging 🤦🏼‍♂️. Let me update the schematic, because I had another version where I wanted to use a TP5100. \$\endgroup\$
    – Sander Slagman
    Commented Aug 2 at 9:33
  • \$\begingroup\$ You also need to provide proper power path management for powering your load while charging to prevent overcharging. Have a good search, there are literally hundreds of questions on here asking the same thing. \$\endgroup\$
    – Finbarr
    Commented Aug 2 at 10:15
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    \$\begingroup\$ @SanderSlagman - Hi, I see you made a substantial change to the question, after receiving an answer to your original question. That isn't allowed, as it becomes a "chameleon question" i.e. it keeps changing. Answers to question rev X look obsolete/incomplete when it gets changed to rev X+1. This can upset those who write answers & can result in your question being ignored / downvoted / flagged for mod attention (and likely closure). Edits can only be used to clarify or improve a question, not change it. || In this situation, where your original question was answered {...} \$\endgroup\$
    – SamGibson ♦
    Commented Aug 6 at 13:21
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    \$\begingroup\$ {...} the correct etiquette is to consider how that question was answered. Then ask a new question, include a link to this original question in your new question & a short narrative explaining what has changed (to avoid people thinking it's a duplicate of the original one). Make sure the new question is complete & "standalone", even though it should contain a link back to this one. || I have reversed the edit here. You can find the added text & image links in the revision history, for you to use in your new question. TY \$\endgroup\$
    – SamGibson ♦
    Commented Aug 6 at 13:23

1 Answer 1

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A Li-ion battery requires two devices:

  1. A BMS
  2. A Charger

A BMS is not a charger. A charger is not a BMS. A linear voltage regulator is not a charger, nor a BMS.

Both devices are required.

You have one: a BMS. You need the other: a charger.

A Li-ion charger does two things:

  • It limits the charging current during bulk charging
  • It limits the battery voltage at the end of charge

A BMS cannot limit the voltage or the current. A BMS is just an On/Off switch.

A standard voltage regulator doesn't limit the current. It does set the voltage, but yours doesn't set it to the correct voltage.

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    \$\begingroup\$ Thanks for the input! \$\endgroup\$
    – Sander Slagman
    Commented Aug 6 at 13:20

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