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[moved] 18650 li-ion charging

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yoosefheidari

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hi
i want to charge 1 cell lithium battery at 2a current because i need faster charging rate.
so i want to parallel 2 tp4056 module.
is that possible?is there any problem?

18650.jpg
 

stenzer

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Hi,

as both TP4056 migth not have the same caracteristics or they differ because of different oparating temperatures you can not expect same "output voltages" during charging process, for the constant voltage period as well as for the constant current period (the voltage drop across the current source might differ). Consequently there might be current flowing from one TP4056 into the output of the other one. To avoid this the use of two diodes might seem to be a "good" choice to protect the individual outputs (anode @ out+, cathode @ bat+). Unfortunately the voltage drop across these diodes will reduce your effective constant current by about ~0.3 V (zener diodes). Ideal diods migth do the job to minimize the voltage drop and to minimize power losses.

BR
 

yoosefheidari

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Hi,

as both TP4056 migth not have the same caracteristics or they differ because of different oparating temperatures you can not expect same "output voltages" during charging process, for the constant voltage period as well as for the constant current period (the voltage drop across the current source might differ). Consequently there might be current flowing from one TP4056 into the output of the other one. To avoid this the use of two diodes might seem to be a "good" choice to protect the individual outputs (anode @ out+, cathode @ bat+). Unfortunately the voltage drop across these diodes will reduce your effective constant current by about ~0.3 V (zener diodes). Ideal diods migth do the job to minimize the voltage drop and to minimize power losses.

BR
from what i realize vary in output voltage is small and it is not harmful for cell at all since maximum current is limited to 2amps and both modules stop charging at 4.2.
the only issue here is current flowing beetwen two modules.am i right?so if two modules connected together works without problem or fails probably there is no need diodes in their output.
 

stenzer

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Hi,

please provide a link to the datasheet of the intended TP4056 to be used, as my websearch results in different manufacturers.

... not harmful for cell at all
that might be true, I do not know which specific cell you are planning to use. Nevertheless, a current-flow from one TP4056 into the other one might result in an undesired behaviour of the "sinking" TP4056. As I do not know the internal structure, not even by means of a functional block diagram, I'm not able to predict how the TP4056 might behave when "supplied" by a current into its output (e.g. applying additional current across a feedback structure).

.... stop charging at 4.2.
This upper limit voltage might even differ between two TP4056 from "start", due to manufacturing prorcess variations. And as already mentioned might even get worse if both TP4056 are operated at different temperatures. You can not guarantee that both will stop charging at the same time instance. So at least you have to connect both standby pins together to stop the charging of both TP4056 at the same time.

BR
 
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