This AEMLION is a 0.8x0.6 inch (20x15mm) PCB with the AEM10941 Solar Harvesting IC from E-peas. It efficiently converts solar 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 into other projects because of small size, castellated via's, and when soldered onto 0.1" pitch header it fits in a breadboard.

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

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 the most power out of the solar cells by doing MPPT maximum power point tracking every 5 seconds.

Specifications

• PCB 2 layers (0.8x0.6inch/20x15mm)
• 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

What you get

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

Warning

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.

Pinout

• SRC - solar panel positive terminal, input to the harvesting IC
• GND - ground
• STATUS - status output pin, open drain output with 1M pull up to 3.3V, active low. When battery voltage falls below 3.6V it goes low 600ms before the 3.3V and 1.8V outputs are disabled. Can be used to warn the host MCU to gracefully terminate writing to EEPROM/flash and prepare for power outage. Voltage level 0/3.3V.
• BAT - connects to Li-Ion battery positive terminal
• 3V3 - regulated output voltage
• 1V8 - regulated output voltage

Adjustable output voltage

The 3.3V output can be lowered to 2.5V. At the same time the battery can be used down to 3.01V in stead of 3.6V. This means you can have a longer battery life! You need to remove R3 and put on the position of R4.

Does it support LiFePo4 batteries?

Officially not, this board is designed for Li-ion, but LiFePo4 is more voltage tolerant, which means it does not get damaged when used between 2.5 and 4.2V. But you need to lower the output voltage to 2.5V. This output is enabled for battery voltages between 3.0V and 4.12V. You need to remove R3 and put on the position of R4.

What is the expected battery charge current?

I have measured AEMLION battery charge current using three different solar panels in indoor light (500 lux), outdoors in the shadow, and in full sun (~500W/m^2).

Indoors (~500 lux) and with the smallest solar cell the battery 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 battery from indoor light but indoor light is really only suitable for very low power applications.

Compatible solar panels

• 1V/80mA 30x25mm
• 2V/160mA 50x50mm
• 4V/140mA 70x70mm

Batteries I have used

• 3.7V 120mAh 4x15x25mm polymer Li-ion Note: Most batteries have a protection circuit that draws 2-4uA.

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.

Testimonials

• Andreas Spies has compared several energy harvesting boards with the AEMLION in this video blog and he is very positive about the AEMLION because it integrates MPPT, a boost converter, battery reverse voltage protection, an LDO/buck converter, and a low energy warning/cutoff.
• Matias Meier from Switzerland wrote blog post about AEMLION. Check it out here.
• SteamIQ was impressed about the AEMLION and tweeted about it here and here.