I2CEncoder V2.1

I2CEncoder V2.1

Solar Harvesting Into Supercapacitors

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The AEMSUCA is a 15x20mm board for the AEM10941 Solar Harvesting IC from E-peas. It efficiently converts solar panel energy into SUperCApacitor charge, it even works with indoor light. It features two regulated outputs that are enabled when the supercapacitor has sufficient charge, and a low voltage warning that informs the user of impending shutdown when the supercapacitors run low. It easily integrates in other projects because of the castellated via's, and when soldered onto 0.1' pitch header it fits in a bread board.

I am also selling two similar boards. One stores its energy in a Li-ion battery and the other in a Li-ion Capacitor. The bare AEM10941 chip I sell here.

This board is special because it integrates maximum power tracking, supercapacitor charging and two regulates outputs in a tiny and easy to integrate board. There's is no other board with so little passive components.

Ideal for indoor applications

The AEM10941 harvesting IC is very suitable for indoor applications because it has an ultra low power startup. The boost converter starts at a very low 380 mV input voltage and 3 uW input power. The IC gets most power out of the solar cells by doing MPPT maximum power point tracking every 5 seconds.


  • PCB 15*20mm
  • solar input voltage 50mV to 5V
  • ultra low power startup 380mV/3uW
  • solar input current max 110mA
  • MPPT every 5 secs, MPPT set to 70%
  • Storage element: you need to connect 2 supercapacitors in series
  • by default the two regulated outputs VHV and VLV are 3.3V/80mA and 1.8V/20mA and are enabled when the supercapacitors voltage has exceeded 3.92V (enabled threshold) and not fallen below 3.60V (disable threshold). The supercapacitors are charged up to 4.5V.
  • the status output pin warns the host MCU if supercapacitor voltage drops below the disable threshold voltage 600ms before shutting down the regulated outputs
  • using a solder jumper you change VHV from 3.3V to 2.5V, see picture. The two outputs are enabled when the supercapacitors voltage has exceeded 3.67V (enabled threshold) and not fallen below 2.8VV (disable threshold). This way you can use a much larger voltage range of the supercapacitor and have a larger battery lifetime.

What you get

  • A soldered and tested AEMSUCA
  • 2x 5pins 0.1" male headers, you need to solder yourself


  • SRC - solar panel positive terminal, input to the harvesting IC
  • GND - ground
  • STATUS - status output pin, open drain output with 1M pull up to VHV (3.3V), active low. When supercapacitor voltage falls below 3.6V it goes low 600ms before the VHV and VLV outputs are disabled. Can be used to warn the host MCU to gracefully terminate writing to EEPROM/flash and prepare for power outage.
  • "+" - Connection to positive terminal of a dual-cell supercapacitor
  • BAL - Connection to mid-point of a dual-cell supercapacitor
  • GND - Connection to negative terminal of a dual-cell supercapacitor
  • VHV - 3.3V with CFG0=0 (default), and 2.5V with CFG0=1
  • VLV - 1.8V regulated output voltage

What is the expected supercapacitor charge current?

I have measured charge current using three different solar panels in indoor light (500 lux), outdoors in the shadow, and in full sun (~500W/m^2 which is not very powerful for full sunlight).

Solar panel indoor 500 lux outdoor shadow outdoor full sun 500W/m^2

Solar panel indoor 500 lux outdoor shadow outdoor full sun 500W/m^2
1V/80mA 30x25mm 50uA 700uA 5mA
2V/100mA 79x28mm 100uA 1.8mA 10mA
4V/100mA 70x70mm 280uA 4.8mA 20mA

Indoors (~500 lux) and with the smallest solar cell the storage element is charged at 50uA for 10 hours. Then the application must have an average current of (50uA*10hrs/24hrs) 20uA or less. That's enough for a simple Bluetooth Low Energy beacon or a very simple LoRa application. If that is not enough you need to select a larger solar panel.

Outdoors, in shadow current is 10-20 times larger. And in sun 100 times larger.

As you can see the AEM10941 can charge a supercapacitors from indoor light but it is suitable ONLY for very low power applications.

Compatible solar panels


The chip max input voltage is 5V. Please be aware that a 5V nominal solar panel can be 6.5V when unloaded. Alway check the solar panel open circuit voltage, or Voc.

Super-capacitors I have used

AVX SCCS30B106PRB 10F 2.7V

How long can an application run supercapacitors?

Rule of thumb: When a 1F supercapacitor is loaded with 1A the voltage will drop 1V in 1second. The AEMSUCA is designed for two supercapacitors in series. It charges the supercapacitors up to 4.5V and the outputs are enabled down to 3.6V. If you have 10F supercapacitors in series then the total capacitance is 1/C = (1/C1 + 1/C2) then you get 5F in total. If your application draws 80mA from the 3.3V output, then it will run for: 5F*(4.5V-3.6V)/0.08A= 56.25s.

How to solder the pin headers?

Use an old bread board, stick the pin headers in and place the PCB on top, then start soldering.

Q&A about supercapacitors

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Jasper Sikken
As a private person I love to share my passion for solar powered an low power electronics circuits