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Charger goes from 1a down do 0.2a when charging 18650
#1
Hello guys,

This is my 1st post in the forum, so I'm not 100% sure if I'm posting on the right place.

I'm a newbie starting in the Battery Pack 'hobby'. Recently I got a bunch of used laptop batteries which seems to be the best way to harvest 18650s.

In one of the laptop batteries I got 12 BAK 18650C4 which accordingly to the cell database can be charged from 440ma all the way up to 2200ma.

I decided to charge one of these BAK 18650 to get familiar with the workflow processing these 18650s.
The charger I'm using is a MC6C XTAR, which accordingly to the spec can charge 3 cells at 1a, or 6 cells at 0.5a.

But like I said, I'm charging only one. When I put the battery in the charger, the LED display show for 3-4 seconds that the battery is been charged at 1a, after that it drops to 0.5a and in my first attempt to charge it went down to 0.2a. The 18650 didn't get hot or anything weird.

I didn't quite understood what / why it happened. Any ideas?

FIY: I charged many others 18650 (I'm a vaper) and I never saw this behaviour.

Thanks!
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#2
Edit: I'm following up really close, the charger went back to 1a and after a few minutes back down to 0.5a
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#3
Sounds like you hit the CV (Constant Voltage) stage of charging.   This is when a battery gets near its top voltage, a charger should avoid going over the max voltage for that type of battery and instead hold steady voltage but gradually reduce the current until the voltage is at the max and the current going into it is 0.   This would be a 'full charge' situation.    The charger's algorithm may be 'testing' the situation - causing the fluctuation between 1.0a and 0.5a - to see what to do.
ERBR1516 likes this post
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#4
Yes, current should taper towards the end of charge cycle holding CV.
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#5
Thanks man, that does makes a lot of sense...

I was worried with something potentially wrong with the battery.
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#6
You can confirm what OffGridInTheCity is saying by connecting a voltmeter to the cell being charged.
The voltage will climb to the charge end voltage (CV) & hover there pulsing occasionally.
Running off solar, DIY & electronics fan :-)
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