Main Page - PhongTPham/Solar-Panel-Project GitHub Wiki
Welcome to the Solar-Panel-Project wiki
The intended purpose of this project was to design, create and test a Solar Powered USB charger. It is meant to be an inexpensive and simple project that could be used for personal use.
QUICK LINKS:
INTRODUCTION
The inspiration for the design of this project came from this project: https://www.instructables.com/id/DIY-Solar-Battery-Charger-1/
The main components I chose to use are:
- A battery charger IC
- A 5V booster
- an SPDT switch to turn charging on and off
- a 1N4007 diode to protect against reverse current
- a 18650 Battery Holder
- a 18650 Battery
- a USB port
- Samsung 5V/2A wireless charger
However, the battery charger and booster are custom made rather than using prebuilt boards. The ICs chosen for this project was somewhat limited as this was a project for a class and it was preferred to keep the parts to Digikey. To avoid going over the Digikey purchase limit, some parts were ordered off of Amazon instead. The rest of wiki will go into the hardware, design, assembly testing, results and future considerations of this project.
HARDWARE
Wireless Charger
Any charger will do, I just had this one hand and decided to use it.
Solar Panel
A 2.5W Solar panel that was supplied to us by our professor. Pretty cheap and common as it is easily found on Amazon. Pretty much made for DIY use.
Battery Charger
The battery charger design was based off of the TP4056 Battery Charger IC. However the IC used was the LTC4052 as that was what was available on Digikey. I chose the LTC4052 because it's functional design is very similar to the TP4056 and also features overcurrent protection. Overall it seemed like a very effective battery charger.
Voltage Booster
The voltage booster design was based off of the LTC3440 5V boost converter. The LTC3440 is a highly efficient DC to DC converter and provides up to 96% efficiency and up to 600mA of output current. Overall a very good voltage booster. The LTC3440 was available on Digkey so we were able to actually use this one.
Battery Charge Protection
My LTC4052 IC has overcurrent protection but the LTC3440 requires protection against conditions like overvolt, undervoltage, overcharge and overcurrent. It's dangerous for a lithium battery to overcharge, over-discharge and discharge too quickly. I was recommended to use a S-8261 paired with a dual package DMG6968 to provide protection to my battery. The MOSFETs of the DMG6968 would disengage and disconnect the battery from the shared ground causing the battery to longer be connected to the boost converter.
Design
I followed the circuit designs I showcased earlier for my battery charger and voltage booster. The simple path I designed can be seen in the block diagram below:
However, I made a mistake with my design of the schematic. I somehow forgot to add in a second USB port to add another charging option for the device aside from the solar panel.
Schematic of the Circuit
PCB Layout of the Circuit
Assembly
Once all my parts that were ordered by our professor arrived I was able to start building right away even though my parts from Amazon got delayed. The resistors, capacitors, inductors and ICs were picked and placed, and then baked within a soldering oven. Any through hole parts were just hand soldered after the PCB was done baking. I then soldered wires from the solar panel to the PCB and just plugged in the wireless charger.
When the parts I ordered from Amazon got delayed and when they did arrive, they didn't include the battery I needed which was a 18650 Battery that I needed. To remedy this a classmate suggested I order an Anker PowerCore 5000 Portable Charger since it would arrive in a short amount of time. While the Anker was being shipped and delivered, I hand soldered my LEDs onto my PCB. Once the Anker came in I took it apart, removed the battery and connected to the pins on my battery holder.
Now the assembly of the device was entirely done.
Link for the Anker PowerCore 5000 Portable Charger
TESTING
After I finished assembling my board I started off simply be seeing if charger worked and it did not; my LEDs for present AC and present charging were also not lit. So this meant I had to do some testing and examining. I noticed there was some solder overflow between the Vin and GND pins of my LTC4052 battery charger IC. I removed this and thankfully the LTC4052 did not fry.
I checked the voltage reading of the solar panel and it read as roughly 0.5V (I was in my room at night with a head lamp so there wasn't much "sun" out). I checked the Vin pin of the LTC4052 IC and it also read roughly 0.5V so this connection worked. I read the voltage of the Anker battery and it was 0.995V and comparing it to the battery pin of the LTC4052 it was roughly around the same at 0.993V. The wireless charger still wasn't charging anything and when I read the Vout and GND of the USB it read as 0 but the charging LED came on now so the solar panel was able to charge the LTC4052 now.
At this point I started to examine the test points 1 and 2 of my PCB, both which read as 0. These test points are connected to the Vin of my LTC3440 voltage booster and my USB out respectively. All of the pins of the LTC3440 read as 0 for current and voltage. I decided to see if the circuit leading up the booster was fine. I checked the voltage readings of my switch and it read 0.865V. The switch follows from the battery and the battery pin of the LTC4052 so this makes sense. However this meant my LTC3440 was not working at all. I checked all the pins and didn't see any bridging. This probably meant that my LTC3440 IC was fried or perhaps was bridging where I could not see it.
To make sure my battery charger IC was working as intended I connected a wire from the pin 1 of the SPDT switch to the power input pin of the USB. Well sure enough the charger did start charging. Just really slowly. The USB power in voltage read the same as the battery which was roughly 1V. So half of this board works but it's kind of pointless without booster to make the charging efficient.
RESULTS
The LTC3440 booster is entirely defunct and as a result any part of the circuit that leads from the LTC3440 is dead. The LTC4052 battery charger functions as intended and can easily be wired straight to the USB to work, but then it loses out on efficiency as it is not being boosted by the LTC3440.
Essentially I have half of a PCB board that works without the voltage booster which is inefficient due to the nature of solar power panels. It's either not sunny enough or the panel is partially obscured. I will probably try this again with some future improvements.
FUTURE CONSIDERATIONS
For future iterations for the project I think these considerations would improve the project:
- The 1N4007 diode is actually not needed since the LTC4052 IC feature reverse current protection
- Add a USB port for the PCB to charge from an outside source such as a wall outlet. Extra functionality is never a bad thing.
- Adding two PCB screw terminal blocks would not be a bad idea as it removes some frustration threading wires through the PCB.
- Order spare parts to substitute fried ICs or defective parts. Since future iterations will be for personal use the only limit is a personal budget limit.
- Making an enclosure to hold all the parts would keep organization neat and offer a more portable way to store the project to use outside of the lab.
I ordered 0805 LEDs off of Amazon because of fast shipping and low cost.
Future iterations of KICAD schematic and PCB will be added below once done .