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Solar harvesting into Li-ion battery

This is a 0.8x0.6 inch board with AEM10941 solar harvesting IC charging a Lithium Ion battery

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The AEMLION is a 0.8x0.6 inch board for the AEM10941 Solar Harvesting IC from E-peas. It efficiently converts solar panel energy into Li-ion battery charge, it even works with indoor light. It features 3.3V and 1.8V regulated outputs that are enabled when the battery has useful charge, and a low battery warning that informs the user of impending shutdown when the battery runs low. It easily integrates in other projects because of the castelllated via's, and when soldered onto 0.1' pitch header it fits in a bread board. I plan to sell this board on Tindie. This project is related to https://hackaday.io/project/159139-tiny-solar-energy-module-tsem and https://hackaday.io/project/160470-solar-harvesting-into-supercapacitors

I designed it because I took part in the HackadayPrize2018 Power Harvesting challenge with a 1x1 inch Tiny Solar Energy Module and found a lot of interest in selling it. However since most projects have different power demands and people want to choose their own solar panel, I decided to remove the onboard solar cells.

This board is special because it integrates maximum power tracking, Li-ion battery 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.

Specifications

  • PCB 2 layers (0.8 x 0.6 inch)
  • 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% (adjustable)
  • Battery: connect your 3.7V Li-Ion battery
  • 3.3V/80mA and 1.8V/20mA regulated outputs. These are enabled when battery voltage is between 3.60V and 4.12V (max charge voltage)
  • battery reverse voltage protection
  • 3.3V status output pin that warns the host MCU if battery voltage drops below 3.60V

  • I have build a simple test rig

    Jasper Sikken09/11/2018 at 20:40 0 comments

    Recently I ordered 50x PCB assemblies from Elecrow that i want to sell on tindie,  but I need a testrig for it. I quickly made one with prototype board, 0.1" headers, a battery, a capacitor, some leds and resistors.

    I just press the board-under-test between the two rows of angled male headers, and then the solar input gets 1.5V from the battery and the LEDs indicate the 3.3 and 1.8V outputs work. Basic functionality checked!

  • I have assembled revision 2 PCBs

    Jasper Sikken09/05/2018 at 19:59 0 comments

    I have received R2 PCBs and assembled one and guess what, it works.

    I have ordered 50x PCB assemblies from Elecrow, it will take 3 week to ship. Now I need to prepare the Tindie page where I will be selling these. 


  • Revision 2 design

    Jasper Sikken08/24/2018 at 19:32 1 comment

    I have received design review comments on revision 1 from E-peas, the harvesting IC manufacturer. They said that the IC signal BUCK should not be accessible to the user because it's an internal voltage that should not be so dirty. In addition I had brought out the SELMPP0 and SELMMP1 signals to the connector that could be connected to BUCK signal.

    I started a new design. I removed BUCK, SELMPP0 and SELMPP1 from the connector. SELMPP0 and SELMPP1 can not be changed externally anymore, they are set to a fixed vallue on board, if you want to change you need the cut a trace on the board and make a solder jumper. I wanted to make the design smaller and cheaper to produce and so I removed the battery voltage measurement divider, if people want it they can add it externally. The circuit already has an output to warn the user of an impeding 3.3V shutdown (STATUS pin) in case the battery runs low.  

    I could shrink the board from 1.0x0.6inch to 0.8x0.6inch.

    I have also added pin names to the silkscreen so the board is easier to use. I have ordered a new set of PCBs from Elecrow for prototyping before I make them assemble a batch of 50 that I want to sell on Tindie,

  • Three boards are assembled and tested

    Jasper Sikken08/21/2018 at 19:12 0 comments

    I have soldered the components onto 3 boards using a solder paste stencil and a hot air gun. 

    They also solder well on to 0.1" header pins for use in a breadboard. 

    Then hardware verification could start. 

    I connected a 20x25mm Li-Ion battery and 1V/100mA 30x25mm solar panel. I measured the 1.8V and 3.3V on the outputs. which only happens when the circuit is able to charge. The solar panel voltage was close to the expected 75% of the open circuit voltage. The battery voltage divider with 4.7M and 10M resistors worked as expected. As well as the mosfet with the status output pin. 

  • I have received revision 1 PCBs

    Jasper Sikken08/20/2018 at 20:13 0 comments

    Today I have received revision 1 PCBs from Elecrow. They look good. I like the black color. I received 13 while I ordered 10.

    In coming days I will solder and test a few. And if all is good I want Elecrow to produce a small batch that I can sell on Tindie. 

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Discussions

Kurt Van Kelst wrote 08/21/2018 at 20:04 point

where do u buy the chips? ....cant find em online

  Are you sure? yes | no

Boris Bershadsky wrote 09/08/2018 at 12:26 point

Kurt, he hasn't made the tindie product page yet...

Jasper, please expedite! I have a bunch of 5V solar cells begging for these chips :)

  Are you sure? yes | no

Jasper Sikken wrote 09/08/2018 at 12:39 point

Hi Boris, thank for liking and following my project. The chips are not available at the large distributors. Here you can buy them from a few distributors. https://e-peas.com/where-to-buy/ I bought them directly from E-pease.

The chip can handle up to 5V, please make sure your solar panel open circuit voltage is below that

  Are you sure? yes | no

Jasper Sikken wrote 09/08/2018 at 12:34 point

These chips are not available at the large distributors. I bought them directly from E-peas, but you can also buy them at distributors listed here. https://e-peas.com/where-to-buy/

  Are you sure? yes | no

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