A highly efficient solar powered Li-ion charger with two regulated outputsDesigned by Jasper Sikken in Netherlands
After the Hackaday post about my Solar Harvesting into Lithium Ion Capacitors board I quickly sold out. I expect new stock End of May 2022.
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 fe…Read More…
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 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.
What you get
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.
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).
|Solar panel||indoor 500 lux||outdoor shadow||outdoor 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.
Solar cells I have used
Batteries I have used
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Please choose wisely between envelope and package. The PCB can be shipped in a bubbles envelope but non-flat items like a capacitor will be crushed in the mail and should be shipped in a package.
Matias | Aug. 13, 2021
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