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Hello everyone is it necessary to have the constant voltage (CV) process when charging 18650 li-ion batteries?

What happen if I usually skip the CV? Does the li-ion battery got memory? I know the CV is needed to charge the battery full but it's really time costing. Thanks

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2 Answers 2

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If you use CC until Vcell is ~= 4.2V then.

  • Cell capacity will be about 80% of maximum

  • Charging time will be about 45 minutes.

  • Cell whole of life capacity stored and recovered will be signifixantly higher due to the gentler charging cycle.

4 hours should be very adequate for a full charge at I max = C.ie Imax =~ 3.2A for 3200 mAh cells. The CC stage will last about 45 minutes leaving 4h-45m = 3h-15m for the CV stage.

If you search SE EE for LiIon charging you will find this area is well covered.

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  • \$\begingroup\$ Thank you very much but I got confused with the third point does it means if I usually skip the CV and in one day I wnat to charge it full then I should use lower current to charge? Thanks \$\endgroup\$
    – user186819
    Jun 25, 2018 at 14:50
  • \$\begingroup\$ 3. Using CC only result is as 3 above. If you follow with CV the cell will set what current it draws. For a fullish charge terminate at I = Imax/2. For more charge terminate at Imax/4. For road warrior very charged use Iterminate = Imax/10. As Iteminate is increased battery life is increasingly reduced. \$\endgroup\$
    – Russell McMahon
    Jun 28, 2018 at 8:01
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Some chargers skip the CV phase for a really 'fast charge', and show 'charge complete' once it reaches terminal voltage. However, it's still not fully charged at that point, and can accept a bit more. If you drove in that last bit of charge as quickly as in the CC phase, then you'd damage the cell by over-volting it, the CV phase is to avoid this damage.

The question is, do you want to use a mostly charged battery very quickly, or do you want to use a fully charged battery but wait a bit longer for it? The choice is yours. It's not necessary to do it either way.

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  • \$\begingroup\$ Thank you for your help. I need to use 3-4 3200mah 18650s everyday during my work and the worst situation I back home at 7:30pm and need to sleep at 11:30 therefore only 4 hours are available to charge the batteries. According to your info then I can only charge the CC if time is not enough and I already got approx 80% of the capacity. And this will not affect the battery in long run as li-ion dont have memory 😁😁 \$\endgroup\$
    – user186819
    Jun 24, 2018 at 10:19
  • \$\begingroup\$ @user186819 Two observations. Four hours ought to be more than enough to accomplish both CC and CV phases, mine are usually fully cooked in an hour. \$\endgroup\$
    – Neil_UK
    Jun 24, 2018 at 11:32
  • \$\begingroup\$ @Neil_UK IF you charge at C then 1 hour is too little for CC + CV chaarge except if the CV terminates at a very high current. eg CC at C for about 70-80% of capacity until V reaches ~= 4.2V is 70-80% x 60 minutes = 42 to 48 minutes. That leaves 12 to 18 minutes for the CV tail - which is rather short if Iterminate is say C/10 oir C/4 but MAY be reached if Iterminate is C/2 or higher.. \$\endgroup\$
    – Russell McMahon
    Jun 24, 2018 at 11:56
  • \$\begingroup\$ I'm planning to charge at 1.5A x4 as this is the maximum output of my charger. 3200/1500=2.13 just hope approx 2-3 hours will be finished. 😁 \$\endgroup\$
    – user186819
    Jun 25, 2018 at 14:45

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