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I have two TP4056 modules (with protection circuit), which I am using to charge two batteries respectively, off a single power line. The modules are the ones that have charge output (B+/B-), and another regular output.

I'd like to be able to use both batteries (increased capacity) to power a single load, even while charging. The batteries are rechargeable 3.7V 16340 Li-ions, same make and capacity.

I'm not sure how to do this in a safe manner. I don't know if it would be safe to conjoin the outputs with this module, and I would like to avoid using diodes because of the voltage drop.

The question is: How can I make this work, in order to be able to use the device even while charging, and how can I connect the two batteries safely to the device in the first place?

My use case is described in the image. charging circuit

EDIT: Look to the comments for an answer regarding more than two cells. As the original question was for two cells, I had to choose one of two valid answers.

Mr.M
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2 Answers2

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Don't.

Just use one TP4056 and connect both cells in parallel after balancing them first. Don't connect batteries with more than 0.2V difference in parallel as this can risk fire and explosions (excessive charging current from one to another).

This will work because Lithium cells have a wide voltage range. So when connected in parallel they will self-balance.

the TP4065 module includes over-discharge protection circuitry power should be taken from the out terminals of the TP4056 module, not directly from the battery.

Parallel connection

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Jasen Слава Україні
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  • Although there is a reduction in charge time to be considered (a single TP4056 is limited to 1A), I doubt my cells can benefit from more than 500-700mA per cell. I will likely choose this as the best answer after researching what you said about self-balance, unless someone gives me a scenario where I can use both TP4056 modules. – Mr.M Jan 31 '18 at 10:26
  • yeah, or maybe you can find a stronger charger module – Jasen Слава Україні Jan 31 '18 at 12:30
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    Works fine as long as one cell is not physically damaged, then it becomes a fire hazard unless fused – Tony Stewart EE75 Jan 31 '18 at 13:50
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    Active Protection IC is the smarter way to go. – Tony Stewart EE75 Jan 31 '18 at 16:27
  • @TonyStewart.EEsince'75 fusing does not prevent the damaged cell from catching fire. TP4056 contains a protection circuit, and yes it should be used, I'll add that to my answer – Jasen Слава Україні Feb 01 '18 at 02:48
  • So I am a bit confused - are both answers doing the same thing now, only @TonyStewart.EEsince'75 is using both modules? Because according to the schematic B- and Out- are not completely common as B- goes through the DW01A and the FS8205A. – Mr.M Feb 01 '18 at 10:35
  • This should work fine. The Protection IC switches off Out- to the load and the Charger IC regulates the Battery on B+, so B- does not go to the load. Just confirm Vbat is matched on each before ganging. – Tony Stewart EE75 Feb 01 '18 at 10:54
  • Jasen's image has an obligatory warning and adds **but we do not recommend connecting more than two cells at a time to this module.** https://www.addicore.com/TP4056-Charger-and-Protection-Module-p/ad310.htm – Tony Stewart EE75 Feb 01 '18 at 11:01
  • When you say 'this' you mean Jasen's edit? – Mr.M Feb 01 '18 at 11:02
  • Yes.... Also there may be problems with 1A USB going to 2 dynamic loads . 2.4A chargers preferred, you may switch accepted. – Tony Stewart EE75 Feb 01 '18 at 11:02
  • Yes, of course. Though, is your answer still valid as well for using two of the modules? – Mr.M Feb 01 '18 at 11:07
  • I am thinking about aging and ganging 2 may be appropriate for retaining matched characteristics rather than divergence, with independent charge levels but 20 in parallel is not appropriate – Tony Stewart EE75 Feb 01 '18 at 11:13
  • So ultimately this solution is better for 2 cells, but your solution would be better for more than 2? – Mr.M Feb 01 '18 at 11:14
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    I think so and the folks at addicore agree. But the thermal voltage characteristics are to raise cell voltage and lower ESR with rising self-heating, there might be a problem charging cold batteries with self-shorting. – Tony Stewart EE75 Feb 01 '18 at 11:15
  • http://www.richtek.com/~/media/Richtek/Design%20Support/Technical%20Documentation/AN024/EN/Version1/image002.gif?file=preview.png This means if the batteries were cold like outside today.. then charged like this, If one heated up faster from higher ESR, the circulation currents between two cells may runaway for a short while – Tony Stewart EE75 Feb 01 '18 at 11:21
  • Note: to balance 2 18650 cells, you can use a 10-100ohm resistor between them and wait until their voltage is close (within .2V); or you can simply charge them independently. – Real Nov 12 '19 at 15:08
  • if you start off with them balanced and connect them in parallel they will stay balanced. For balancing a 10 ohm resistor seems excessive because the voltage difference will be less than 1V, so a resistor of 1 ohm or even less should be fine. – Jasen Слава Україні Nov 14 '19 at 02:24
  • Also bear in mind that the 4056 measures the current to determine the cutoff point. if you have 2 or more batteries in parallel the total resistance of the batteries will be reduced and so the cutoff point will be higher than the 100mA threshold the chip is looking for. This could lead to overcharging. – nick fox Jan 24 '20 at 14:31
  • it's impossible to overcharge a lithium ion battery in constant voltage mode, but the current limits can be set by reducing the resistor or pin 5 to get faster charging and earlier termination. – Jasen Слава Україні Jan 24 '20 at 18:45
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Solution

Be able to use both batteries (increased capacity) to power a single load with two TP4056 modules.

dxdev.co.nf
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    It would be much easier to interpret this is you used a proper switch symbol instead of a photograph. Are we supposed to guess the pinout? I can't even tell if your circuit is correct. Moreover, I really don't think the initial poster had a manual switch solution in mind. – dim Mar 03 '19 at 22:06