A highly efficient solar powered Li-Ion Capacitor chargerDesigned by Jasper Sikken in Netherlands
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 battery...Read More…
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.
The AEMLIC is a 15x20mm 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 one regulated 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. It easily integrates in other projects because of the castellated via's, and when soldered onto 0.1' pitch headers it fits in a bread board.
This board is ideal for solar powered BLE or LoRa connected sensors because it integrates maximum power tracking, LIC charging, and it has a regulated voltage output in a tiny and easy to integrate board.
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.
What you get
What is the expected 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|
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 from indoor light but it is suitable ONLY for very low power applications like LoRa and BLE. This board is also suitable ONLY for low voltage chips because the regulated output is 2.2V. Many modern microcontrollers, LoRa, and BLE chips have an 1.8-3.6 operationg voltage range. The AEM10941 is NOT suitable for power hungry WiFi/2G/4G applications, because those require minimal 2.5V and 150mA.
Solar cells I have used with this board
Lithium Ion Capacitors I have used
How long can an application run on a fully charged Lithium Ion Capacitor?
Rule of thumb: When a 1F capacitor is loaded with 1A the voltage will drop 1V in 1 second. The AEMLIC charges the capacitor up to 3.78V and the output is enabled down to 2.49V. If your application draws 30mA from the 2.2V output, then it will run for: 30F*(3.78V-2.49V)/0.03A= 1290s = 21.5 mins
Can the LDO be set to 3.3V?
Yes, it is possible to adjust the AEM10941 voltage levels by changing the values of R1 to R6. You need to dive into E-pease AEM10941 datasheet and use their Configuration Tool to calculate the right values and you need to have SMT soldering skills. The disadvantage of increasing the LDO output voltage to 3.3V is that you cannot use the full LIC voltage range (2.5 to 3.8V) and so on 3.3V your application will run 7 times shorter than on 2.2V. : 30F*(3.78V-3.6V)/0.03A= 180 secs = 3 mins
Is is possible adjust the voltage levels?
Yes, by changing the values of R1 to R6. You need to dive into E-pease AEM10941 datasheet and use their Configuration Tool to calculate the right values and you need to have SMT soldering skills. Please also use 1% tolerance resistors.
How does LIC compare to other storage devices?
Compared to Li-ion LICs are non-toxic, don't need protection circuits, they don't have shipping resistictions and can be disposed with normal electronics. Compared to supercapacitors LICs have much higher energy density. Please see one of the images to see a comparison table with Li-ion and supercapacitor.
Solar harvesting into Lithium Ion Capacitor - In the news!
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