Project: Recycling cell phone batteries for solar power
Part 1 video on YouTube | Part 2 video on YouTube
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A second chance for discarded batteries
Some time ago, a friend sent me a box of discarded lithium-ion cell phone batteries he had no use for. They would have ended up in the landfill otherwise. So I started a “side project” in which I intended to experimentally use these batteries for solar power. Normally I use LiFePo4 cells for solar power, the type of Lithium-ion chemistry in cell phones makes me very nervous. But you don’t know if you don’t try.
I spent a few days cracking and ripping the battery cases open using my hands, clamps and a hammer, and getting sore thumbs in the process. The cells inside were difficult to work with, often the bus bars would detach from the spot welds, leaving only an aluminum can – so no hope of soldering to it. I do not own a spot weld machine.
Construction Details
After having a look at the cells inside, I discovered many different form factors but nearly all of them were flat and rectangular. So I used kapton tape, nickel strip and plastic cards to sandwich the batteries in layers.
Each battery had a pair of 5A fuses soldered to them. This ended up being the fastest way to make connections to the cells. The 5A fuses should easily blow if something goes wrong with a particular cell. There is also a main fuse for the entire parallel stack.
Unfortunately, on some of the cells I was forced to solder to the can (metal cell case), heating it up. The trick here is to use high heat, leaded solder (rosin core) and move fast. Note: soldering to cell phone batteries is highly risky and NOT recommended due to the volatility of the chemistry.
The end result was multiple stacks of cells sandwiched together as one 3.7v battery bank. I then took these stacks and placed them inside of empty standard-group-size plastic battery cases. Although these cases are a bit overpriced in my opinion, they look very nice and professional.
The batteries took a charge just fine. I did not use a BMS (battery management system) but will use a Battery Monitoring System. Balancing, if any, will take place outside the battery boxes. No active or electronic components are inside. Keeping it simple makes a safer experiment.
No BMS
You might wonder why I don’t use a BMS. This deserves to be addressed separately. But in short, I have successfully operated large lithium solar power banks with no BMS at all for many years – and I have no desire to use one unless it makes sense. Going without a BMS requires a premium effort when doing the initial battery bank setup, strict operational controls and an understanding of why the battery bahaves as it does. And a willingness to to break free from popular conventional wisdom. Perhaps I will make a video or post about this topic later.
End Result
Bottom line, the batteries work fine and take a charge. They even look nice. So what are these experimental recycled batteries good for? Light duty tasks only – small inverter, security and emergency lighting, cell phone charging etc. I would not use them for heavy work. They are low C-rate cells, perfect for powering a cell phone but not good for high amperage draw.
The best part is these junk batteries will live on as a useful power storage system. If I take good care of them and don’t abuse them, they should last many years of service.
I hope you enjoyed reading this article. If you are curious to see what the batteries look like, check out the videos below. If you have any questions or comments, please feel free to let me know. Thanks and have a good day! -DD
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