Solar harvesting into Lithium Ion Capacitor

A tiny board with AEM10941 solar harvesting IC charging a Lithium Ion Capacitor

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jaspersikken has 392 orders / 15reviews
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I designed this board because of a recent price drop in Lithium Ion Capacitors (LICs) and I believe LICs combine many advantages of Li-ion and supercapacitors making it a perfect choice for batteryless IoT applications. On April 26th 2021 I started selling on Tindie.

This is a 15*20mm board with the AEM10941 Solar Harvesting IC from E-peas. It efficiently converts solar panel energy into LIC charge, it even works with indoor light. It has a regulated 2.2V output that is enabled when the LIC has sufficient charge, and a low voltage warning that informs the user of impending shutdown when the LIC runs low. Compared to Li-ion LICs are non-toxic, don't need protection circuits, they don't have shipping restrictions and can be disposed with normal electronics. Compared to supercapacitors LICs have much higher energy density. Let's get rid off batteries.

Solar harvesting into Lithium Ion Capacitor

This board is similar to my Solar Harvesting into Li-ion and Solar Harvesting into Supercapacitors board, but this one is designed to store its energy in a Lithium Ion Capacitor. 

I have ordered this 30F and this 100F 3.8V Lithium Ion Capacitor from manufacturer Vinatech. In qty100 the price is 3.06 and 5.08 USD respectively.  The usable voltage range is 2.5 to 3.8V. 

On the PCB the AEM10941 is configured to keep the LIC voltage between 2.5V and 3.8V, using resistors R1 to R4, see below. 

The LDO output voltage was set to 2.2V (2.5-0.3V voltage drop for de LDO) using resistors R5 and R6.

When the voltage exceeds 2.6V (Vchrdy) the output LDO is enabled and when the voltage falls below 2.5V (Vovdis) it is disabled. The 2.2V regulated voltage is suitable for many low power chips. Many LoRa and BLE chips work on voltages between 1.8V and 3.6V.

The resistor values were selected using the E-peas configuration tool

This is the full schematic off the board. 

For the prototype bare PCBs were ordered from JLCPCB

I have assembled the board using hot air gun

After that I have soldered the board to 0.1" pitch male header connectors, sticked it into a small bread board, connected a 50x50mm solar panel and a 30F 3.8V Vinatech Lithium Ion Capacitor

And it worked, it charged the LIC and after a while the 2.2V LDO output was enabled. I have verified all voltage levels. After this test I waited few days before ordering a batch 100 PCBAs from Elecrow.


Bill of Materials, PCB specification, placement file, assembly drawing

sheet - 60.53 kB - 04/15/2021 at 15:03



Eagle schematic design file

sch - 151.63 kB - 04/15/2021 at 14:59



Eagle layout design file

brd - 63.52 kB - 04/15/2021 at 14:59


x-zip-compressed - 22.41 kB - 04/15/2021 at 14:58


  • Just received the first batch of 100

    Jasper Sikken04/26/2021 at 19:44 0 comments

    Today I have received a box with 100 PCB assemblies from Elecrow from China. 

    I have functionally tested 10 pieces and all works well. 

    And now I have put it for sale on Tindie. It is still waiting approval. 

  • PCB assembly is in progress

    Jasper Sikken04/15/2021 at 19:33 0 comments

    The Chinese PCB assembler Elecrow has recently shared with me the pictures of the panel and of the first assembled board, for my approval. 

    I see some solder mask issues between the pads of the IC but Elecrow assured with me there is no problem and that there will be no short circuits. 

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Kevin Stuart wrote 09/17/2021 at 21:03 point

Excellent writeup!  (I've already ordered my board from your site.)

If I could ask, why did you set the MPPT to 70%?  With the first solar cell (1V/80mA), I see that Vmp = 1V with Voc = 1.2V, so I would have thought that you'd set MPPT to 75% or 85% (out of the 70, 75, 85, 90% options) since Vmp/Voc = ~83%.

Did you actually measure a different Voc than the stated value?  (I see on the 2nd solar cell (2V/160mA) that they measure Voc = 2.3V but spec Voc = 2V it would appear.)

  Are you sure? yes | no

Jasper Sikken wrote 10/17/2021 at 07:04 point

Hi Kevin, sorry for the late reply. Theoretically 80% is better, but I set mppt to 70% because during a real life test I learned battery charge current was highest at 70%.

  Are you sure? yes | no

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