This question is an exact duplicate of:

I have build this UPS battery supply to power a Raspberry Pi using 18650 batteries,using the TP4056 battery charge controller. The circuit as follows:

enter image description here

This is working fine at the moment, but I'm worried: Is the charging and discharging of the battery occurring at the same time? Will this effect the batteries and its life?

And also there is only One battery protection IC for three single batteries,Will this is a suggestible way for protecting multiple batteries,And i'm thinking of replacing the USB/DC charge adapter with Solar panel 6V,14W, will this be able to accomplish the task?


marked as duplicate by Chris Stratton, Dave Tweed Aug 9 '18 at 20:49

This question was marked as an exact duplicate of an existing question.

migrated from raspberrypi.stackexchange.com Jul 14 '18 at 17:09

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  • 1
    \$\begingroup\$ You have already asked about 8 or 9 questions on this same topic. If you have new material, please add it to the original question rather than starting a new one. \$\endgroup\$ – Dave Tweed Aug 9 '18 at 20:51

First obvious question, why do you have three TP4056? They are not designed to be connected in parallel, their outputs will affect feedback and therefore distort proper charging profile.

Second, it does not look like TP4056 is designed to be used with system load connected. You need more advanced BMS to have this functionality. The functionality is called "Power Path".

MCP73871 is an example of charge controller that can do what you need.

And here is AN1149 application note that can answer all your questions. Note that application note uses different controller (MCP73837). The MCP73871 already has most of those external components inside. This is just for the reference, to better understand the potential problems and see how they are resolved.


Using solar panel as external source presents several problems.

First, 7V is absolute maximum for MCP73871, meaning it will survive but not for long. So, you'd need 6V external voltage limiter (e.g. zener-based) for the times when solar panel output is too high.

Second, very often the panel output will be less than 4.5V required for charging, meaning your battery will only be charged in bright light.

Third, peak available power means very little for CC/CV charging profile of the LiPo battery. You either using very little of it, or you can use much more than 2A, depending on the current stage of charging.

The only way I see to solve all these problems is to use MPPT like SM72441 between the panel and BMS.

  • The MPPT can be programmed for fixed 6V output. It will boost the voltage in low light and limit it in bright light with about 99% efficiency.
  • It will keep solar panel at maximum power point. You won't be using "peak available power", you will be using maximum available power at all times.

You can buy ready-made MPPT modules for just a few bucks (no guarantee of quality though) or design your own.

  • \$\begingroup\$ Thanks for the answer, i used few TP4056 IC's, as the current required for charging the batteries stack may not be sufficient. \$\endgroup\$ – Shiv Jul 14 '18 at 17:44
  • \$\begingroup\$ " it does not look like TP4056 is designed to be used with system load connected. You need more advanced BMS to have this functionality." Why I cannot use this TP4056 as the battery management system, could you tell me what are the efficient BMS? \$\endgroup\$ – Shiv Jul 14 '18 at 17:47
  • \$\begingroup\$ As long as charger supplies any current it will be sufficient to charge the battery, it will just take long time. But you are trying to use charge current as system power source simultaneously. It does not work this way. I've updated the answer with an example of proper BMS \$\endgroup\$ – Maple Jul 14 '18 at 17:57
  • \$\begingroup\$ Thanks for the information. I have gone through the link you have sent, it is matching our requirements,But my only question is we need to charge multple cells,instead of a single Li-ion cell, that will be connected in parallel.Doez it support charging parallel Li ion cells of each 2200mAh. \$\endgroup\$ – Shiv Jul 14 '18 at 18:03
  • \$\begingroup\$ With parallel connection BMS does not see separate cells, it sees one big cell, same as your DW01A. Which, by the way, I'd rather replace with 3 individual protection circuits. Also series fuses sometimes added to parallel cells to disconnect a faulty cell from the pack. I suggest looking at this question and links in it. It is almost exactly your project. \$\endgroup\$ – Maple Jul 14 '18 at 20:19

Is the charging and discharging of the battery occurring at the same time? Will this effect the batteries and its life?

When a load is connected while charging, the charger is effectively supply the load and the charge rate is reduced.

You have a setup with Ibat = 1000mA from each Rprog=1.2k thus a curent source of 3A that switches to CV at 4.2V

The uncertainty of performance is that the strongest battery (lowest ESR) will share more than 1/3 of the 3A load , so the ESR's ought to be fairly well matched if you are pushing the charge rate to the recommended limit.

If so, I think it may accelerate aging of the strongest cell, and tend to equalize the ESR to the weakest cell.


So as the mismatch in ESR increases , be more conservative on the charge rate. Charge rate, achieving lifetime charge cycles and %DoD are always user choice tradeoffs. Test the voltage drop with repeated 1A load pulses to estimate ESR.

You will need a large heatsink. > 10W.

  • \$\begingroup\$ If you dont like it explain why. Otherwise I assume you understand nothing, \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 10 '18 at 4:10

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