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Forum: Analog Circuits Li Ion charge only with CV - what happens


Author: vwilde (Guest)
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Hi, my name is Victor. I'm german but try it in english.

I have a solarcell and an TP4056 IC for example. (I know its not good 
setup). The voltage is termined by IC and the max current by resistor. 
Althing work (not fine) but "ok".

My question is what happens with the 1S 18650 cell with that setup? The 
CV ist ok. But there is no possibility for CC.
What changes with the 18650 for example: Lifetime? Capacity? other 
difficulty?

Is a fluctuating current input so significant for e.g. NCR18650B Cell?
Why CC recomend? If you can give me a good link in german or english 
with researches or information from a producer like panasonic/sony/... 
would be great. Or if you have do test and could share would be really 
great.
I couldnt found something like that in web.

Best regards

: Moved by Admin
Author: David W. (harvesthor)
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Here are some specs of your cell:
https://www.batteryspace.com/prod-specs/NCR18650B.pdf

CC is recommended because it has the highest charge speed without 
hitting a critical limit. The NCR18650B has a maximum charging current 
of 1625mA. If you limit this current by a ((4.2V-3V)/1.65A) 750mohm 
resistor, you get a significant lower charging rate. However low 
charging rate is always good for cycle life but with a limiting 
resistor, you still have a higher maximum current compared to a CC with 
the same charge speed, so even if you want to limit current for better 
cycle life you can have better results with CC instead of a resistor.

But in your case, the TP4056 has a CC setting. You can set it over a 
resistor. Also, you can check the maximum current which the solar cell 
can deliver. If this current is not higher than the rated charge 
current, there is no need to limit it afterward.

Author: Li+++ (Guest)
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David W. wrote:
> However low
> charging rate is always good for cycle life

Having a very low charging rate near the cut-off voltage might actually 
decrease the cycle life..

Author: Manfred (Guest)
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vwilde wrote:
> I'm german but try it in english.

Crazy, in a German forum?

To understnd the 4056, please look fr this:
Youtube-Video "Charging a Lithium 18650 Cell using the TP4056"

Der TP4056 startet mit Konstantstrom, wozu sonst hat er wohl den 
Widerstand? Deine Frage ist ziemlich unklar.

Author: onemintyulep (Guest)
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The cell doesn't care if the charge current is variable. The "CC" just 
means limiting the current so that neither the Charger nor the Cell is 
outside of its specification. For the cell that usually means 0.5C to 
get the nominal cycle life.

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