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I want to make a circuit using solar panels. I want to recharge e 11Volt 1200mAh rechargeable battery with my solar circuit. The solar panel I will be using is 5volt, 30mAh. So my question is, how can I construct the solar circuit- how should I use multiple solar cells parallelly and serially to ensure that the circuit generates more than 11 volts. 1) should I just serially connect 3 solar cells to make 15 volts, 30 mAh, should there be any other electrical components? 2)after establishing the circuit, should I just connect the two ends of my solar circuit to the positive and negative of the rechargeable battery? Or should there be any transistor, diode or something else in the middle to ensure the flow? 3)can I use the battery to power an arduino at the same time the battery is getting charged? Or should the charging and discharging be in a different time? 4)If I have to do charging and discharging at the same time, what measures should I take to ensure it? I will highly appreciate if any of you can come forward and help me. And if you have a picture of the said circuit or any link, I will be grateful if you attach it to the replies.

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  • \$\begingroup\$ There are no 11V rechargeable batteries ! :-) :-(. || Tell us the chemistry and number of cells. || 3 x LiIon cells = 3S configuration = 3 x 3.7V = 11.1V NOMINAL / average) but actually 3 x 4.2 = 12.6V FULLY charged and 3 x 3V = 9V fully discharged. | Charging LiIon without a proper LiIon charger will almost always destyroy them very rapidly. || If you have 3S LiIon you want a 3S LiIon charger. | You COULD build one but it's usually better to but one pebuilt. \$\endgroup\$ – Russell McMahon Sep 23 '19 at 6:47
  • \$\begingroup\$ 3s configurion it is. Can you kindly tell me how to use the 3s lion charger with solar cells? and how do i use the solar cells combination as well? please and thank you \$\endgroup\$ – Mainul Hossain Sep 23 '19 at 7:16
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Go read properties of recommended Lithium charge specs. Then compare with all that you have.

11V x 1200mAh = 13.2Wh.
3 x 5v x 30mA = 0.45W @ 15V. (Rated).
- 3x 3V x 30mA = 0.9W @ 9V when Vbat @ 0 % SOC

Understand that the specs for charge profile on Lithium cells are :

a) CC mode until 4.2V/cell

  • this assumes all cells are balanced so if string is 12.6V, no cell >4,2 which degrades MTBF. Then switches from CC to CV mode
  • CV mode @ 4.2V/cell must cutoff charger when Ichg reduces to 3% of 1C or <0.03 x 1200mA<= 36mA which your PV cannot supply
  • There is a time limit spent above resting voltage at 100% SoC or > 3.8V since this also reduces MTBF exponentially with voltage.
    • Normally this time from 3.8V to CV to cutoff is about <<15 minutes at 1A charge rate with no load to to increase capacity est. 80 to 100% SoC. But at 20~30mA charge rate this is only 2~3% of 1.2A = 1C charge rate., so you cannot reach 4.2V in < 15 min. after 3.8V

So with grossly underpowered PV charger. I suggest you limit charge voltage to 3.8V and suffer loss of maH capacity ( est.20% initially , more over time)

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  • \$\begingroup\$ so, can you kindly tell me what are your suggestion? my constraint is that i have to solar cells and have to charge the said battery. Do i need to add any component in the circuit and how so? \$\endgroup\$ – Mainul Hossain Sep 23 '19 at 8:28
  • \$\begingroup\$ For this puny charger, use same circuit as garden lamps with a voltage limiter such as a Series Reverse blocking diode then a shunt Zener on each PV \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Sep 23 '19 at 10:44
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Introduction:

While this answer addresses the specifc case of charging a 3S Lithium battery from multiple small PV panels, the material covered is applicable to many small solar charging applications.

If desired the TP4056 charger IC could be used to make one's own single cell LiIon charger "from scratch" (just as one could make one's own PV panels from sand plus a few other materials :-) ) BUT as the complete modules area available for less that the cost of the components, it makes sense to use them.
If desired, other LiIon charger ICs could be used in this manner.

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I want to recharge a 3S 1200mAh Lithium Ion battery rechargeable battery with my solar circuit.
The solar panel I will be using is 5volt, 30mAh.
How should I use multiple solar cells parallelly and serially to ensure that the circuit

3 x LiIon cells = 3S configuration = 3 x 3.7V = 11.1V NOMINAL / average)
but actually 3 x 4.2 = 12.6V FULLY charged
and 3 x 3V = 9V fully discharged.

Charging LiIon without a proper LiIon charger will almost always destroy them very rapidly. If you have 3S LiIon you want a 3S LiIon charger. You COULD build one but it's usually better to but one prebuilt.


A simple "off the shelf" solution is to use a separate solar charger per cell using TP4056 or TP5100 charging modules. TP4056 allows up to 6V input - 5V is better due to thermal issues. TP5100 allows up to 18V input with a builtin switching regulator.
3 x TP4056 modules would meet your need.

Connect multiple parallel PV cells to TP4056 input.
Connect TP4056 battery output across 1 cell.
Connect 3 x cells in series with 3 x the above arrangement, one per cell. Use as many parallel 5V panels per cell to provide current of choice.

enter image description here

The image shows the use of modules with protection circuitry equipped. In this application modules without protection circuitry are just as good.

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TP4056 charging boards can be obtained in Pakistan from
With onboard output protection here
This version is recommended for single cell use as the output is "protected" against low battery over-discharge. It makes no difference when series connecting cells

or

Without protection circuitry from here

and no doubt elsewhere.

I found no TP5100s advertised in Pakistann - but Ali Express has many eg here

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