What is charging time for Li-ion battery: Li-ion 18650 3,7V 1800 mAh
AC/DC adapter Charger: 4,2V 500mA
No built-in protections against overcharging, over-discharging.
As per my calculation, I get ~ 5 hours 24 min.
Show your work. That seems way too long.
a7
1800/500 = 3.6 hours IF we (unrealistically) ASSUME 100% efficiency and constant 500mA.
The battery MIGHT has a thermal fuse or other built-in protection so it doesn't catch fire.
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This should help a lot: https://www.digikey.com/en/articles/a-designer-guide-fast-lithium-ion-battery-charging
I used this formula:
charge time = rated capacity/charge current x factor. The factor is usually set 1.5
So, for 1800mAh battery, approximate 5.4-hour charge time with 500mA charger (1800÷500×1.5).
Some sources advise just to add 0.5-1 hours at the end:
nominal capacity / charging current + 1h.
A factor is useful. In this case using 1.5 is very conservative, so you've calculated what might be a very generous allowance for charging.
But as @DVDdoug reminds us, theory is one thing, factor or no. The only way to know with a certainty you might want to rely on is to test the actual cell or battery with the charger you are going to use.
a7
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There is no rule of thumb, it depends on the charger.
The best answer will come from the manufacturer. Most have a service department that will help you. They know there product better then most.
Why not just buy good batteries from a reliable source . Perform well, last a long time , good capacity , safe etc , won’t leak .
Saves you trying to work out capacity , which I guess you want to do because you don’t trust your purchase .
Good batteries are not expensive.
Indeet the tecnical data from battery manufaturer should help.
My experience with Li batteries is, that the factor is less then 1.1. And this plus something like an hour depends heavily of the inner resistans of the battery, which normally (new or good taken care for) should be very low and then not really adds needed time. Plus 10 minutes might be already more then enough.
Best is, to observe the voltage during the charging. Then you see the point, where the battery is fully charged, because the voltage suddenly rises from 3.x V to over 4.0 V. When 4.2 V is reached it´s better switched off. Any more time just adds stess and wear to the battery.
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