I bought a 2 brand new pcb protected 18650 cells (UR18650RX) about 4 months ago that I had planned to use in a build. Before I got going I measured their voltages and both we're on 3.58v, not ideal (below 3.6 empty voltage) but I'd thought I'd charge them up; left them about 4 hours on charge and when I got back I noticed they had not charged at all (they stil measured 3.58v). The charger I used is the HX-2S-01 BMS configured in the following manner:

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I measured the voltage on the P+ and P- tabs and they are getting the required 8.4v.

I checked out a few articles and videos and most mentioned to take a good, charged 18650 cell, connect it in parralel to the "sleeping" cell and keep it there until the dead cell measures ideally 3.6+ then put in on nomral charge. I do not have a good 18650 cell with me, and so I came about an bloke that mentioed I can use a quick 3-5 seconds jolt from a 9V battery to "wake" the cell. Is this safe?

I have a varibale 3-12V 1A DC adapter, maybe I can try and wake it with that instead?

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    \$\begingroup\$ No, it is not safe. You can overcharge the cell, and destroy the protection IC. \$\endgroup\$
    – Lior Bilia
    Commented May 11, 2020 at 12:08
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    \$\begingroup\$ What charger did you use? Sounds like it isn't charging at all. At 3.58V there is no reason it shouldn't charge the cell. Also exactly which 18650 size cells are they? \$\endgroup\$ Commented May 11, 2020 at 12:11
  • \$\begingroup\$ You will need to provide us a link to the cell and its BMS. I would also not recommend to short a 9V and a 18650 cell. You need a proper charger for a 18650 cell. \$\endgroup\$ Commented May 11, 2020 at 12:11
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    \$\begingroup\$ This "waking a cell" scheme works with the very old NiCd cells that could develop a short when discharged too low. Then the cell would have a very low, close to zero voltage. Don't do this to any Lithium based cell. Also there is no need. My guess: your charger is broken or doesn't make good contact. Just don't experiment with Li-Ion cells. Only treat them the proper way. \$\endgroup\$ Commented May 11, 2020 at 12:12
  • \$\begingroup\$ Updated post to include BMS and Battery Specs \$\endgroup\$ Commented May 11, 2020 at 12:26

1 Answer 1

  1. Don't use BMS for charging. BMS can balance cell and protect over charge and over discharge but it not designed for charging. To charge the cell you need constant current while cell bellow 4.2 and then switch to constant voltage. so use proper charger.
  2. 18650 can be get in protect mode when it under voltage or over current and it can reset by normal recharge (also BMS module act the same way)
  3. I see many video about revive under voltage li-po cell some time called dead cell it use constant current to charge it up until it reach chargable voltage and then switch to normal li-po mode with very low current so don't use direct voltage to charge li-po cell we need to limit the charging current.
  • \$\begingroup\$ I see thank you. What constitutes a "proper charger" though? I thought if you are building a 18650 project and need a way to recharge the batteries while they are embedded in the system you need a bms board so they can be safeley charged by an input voltage and safeley discharged by the system when their fully charged and input voltage has been removed. \$\endgroup\$ Commented May 11, 2020 at 14:30
  • \$\begingroup\$ In prototype phase I usually use programmable charger which can adjust voltage and current pretty handy you should have one. in this case you can use CC CV regulator module which can adjust voltage and current to match your cells. \$\endgroup\$
    – M lab
    Commented May 11, 2020 at 15:04

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