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I want to charge 3 separate 18650 cells with one charger. Each one of the batteries has their own TP4056 module. So in total there are 3 TP4056's. I know that TP4056 is rated at 1 amp input, though my USB charger only puts out 2 amps. I want to use USB male to 3 Micro USB splitter, to charge each battery equally, and by doing calculation: 2/3=0.666, each battery only gets 0.666 amps. So is 0.666A enough for TP4056 to charge a 18650 battery?

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  • \$\begingroup\$ You can even charge an 18650 cell with 0.1A (100mA) or even 66 mA if you like, it will simply take longer for the cell to charge. Note that you have to change a resistor in the TP4056's circuit to make it charge with a specific current. See the TP4056 datasheet how that's done. \$\endgroup\$ – Bimpelrekkie Jan 13 at 14:19
  • \$\begingroup\$ So without changing resistor it isn't possible? \$\endgroup\$ – Spoods Jan 13 at 14:34
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    \$\begingroup\$ I would not say "not possible" but maybe "asking for trouble". The current taken by a TP4056 depends on the input voltage and the battery voltage. If you do not change the resistors to limit the charging current of the TP4056 to for example 0.6A then there can be a situation where all chargers want 1 A. The USB adapter might 1) just not deliver that and shut off 2) it might reduce the voltage 3) it might overheat. What happens depends on the quality of the USB charger. You should not risk overloading and change the resistors so 0.6A is the highest current. \$\endgroup\$ – Bimpelrekkie Jan 13 at 19:34
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From the TP4056 datasheet:

Programmable Charge Current Up to 1000mA

That means the TP4056 is able to handle charge currents from 0 to 1A (1000 mA). If you're only able to supply it with 2/3A (~666mA), so be it. All that happens is that it will take longer time to charge the cell/s.

Edit: As pointed out by Bimpelrekkie, you have to make sure that the USB charger you have in mind for this application behaves properly when subjected to this heavy current draw. But still, the answer to your question "is 0.666A enough for TP4056 to charge a 18650 battery?" is Yes, you can charge a 18650 cell using less than 1A of supply current.

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    \$\begingroup\$ This is not a good answer as the 3 TP4056 modules and the battery voltages determine the current. If these all want 1 A then 3 A needs to be delivered. The USB charger has a 2 A rating. There is no way to tell what happens when you ask 3A from that charger. Worst case: it overloads and causes fire. Is that risk worth charging a little bit faster? \$\endgroup\$ – Bimpelrekkie Jan 13 at 19:37
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    \$\begingroup\$ This is a matter of determining responsibility. The USB charger is responsible for not catching fire if overloaded. So is the charging circuit, and it does that by limiting its charge current to 1A. As you mentioned, this may result in the USB charger taking some action to protect itself, where one result could be that it limits its current output to 2A. If you would alter the charging circuit to just supply 2/3A, then you also limit future upgrade possibilities, like for instance replacing the 2A charger with a 3A version. \$\endgroup\$ – Eriond Jan 13 at 21:12
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    \$\begingroup\$ This is a matter of determining responsibility. Indeed, as a user you have the responsibility not to use devices outside their ratings. In an ideal world the charger would indeed shut off before overloading. In the real world few chargers have such overload protection. And your "limiting upgrade possibilities" is a moot point, then just change the resistors back to their original value. \$\endgroup\$ – Bimpelrekkie Jan 13 at 21:27
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    \$\begingroup\$ This is the right answer. The charger will deliver up to 2A and the batteries will take up to 1A. They'll share whatever the charger manages to deliver, though without any guarantee of efficiency. Provided the charger has overcurrent protection, everything will survive. If it doesn't, it may fry itself, but the batteries will be fine. \$\endgroup\$ – Heath Raftery Jan 13 at 23:09
  • \$\begingroup\$ One other thing to be mentioned about allowing the batteries to share input in this way, is that there is not remotely a guarantee that they will charge at the same rate, so assuming it works, one battery may complete it's charge cycle before the others. \$\endgroup\$ – K H Jan 14 at 4:26

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