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I recently found a dead laptop battery and disassembled it, found 6 batteries of CGR18650. So when I checked with them my multimeter, they had quite bit of voltage. So I decided to charge them, since I didn't want to spend money for a charger, I decided to make one. found This, I made it and now I'm able to charge my batteries. I'm watching charging current using my multimeter. So I found LM339N voltage comparator IC inside a broken power-supply and the IC is working.

Here's the sketch of charging circuit, enter image description here

So how do I modify my charging circuit with LM339N, I'm not an expert in electronics. So my knowledge is limited. Since I don't want my multimeter to be connected with the battery to measure current, I want to make some led bulbs glow when the charging is completed.

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You do not use the voltage of a charging lithium battery to see if it is fully charged, instead you detect when the charging current has dropped low. The voltage shoots up quickly when charging so when the voltage is high then the battery is nowhere near fully charged. You MUST limit the charging voltage to 4.20V or a little less (3.73V is much too low) and limit the charging current to avoid an explosion.

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  • \$\begingroup\$ I see. So I should be monitoring current then? \$\endgroup\$ – Aimkiller Sep 22 '18 at 4:54
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I could achieved this with using a LM358 comparator IC.

using the above circuit I'm able to charge the battery, but the problem was I don't when it fully charges and over-charge. So using LM358 as a comparator, I could solve the problem.

I used a voltage divider using a 5v supply to get a 3.73v. I powered up the above circuit through a relay, so while the battery voltage is below 3.73v the relay will be on. when the battery voltage becomes 3.73v the comparator will turn off the relay and protect the battery from overcharging

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    \$\begingroup\$ Can you please give more explanation. It is nice that you've solved your problem, however, you can improve the answer by adding more information so that if anyone finds this thread can get an informative answer. \$\endgroup\$ – Hazem Jul 1 '18 at 18:27

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