Sid Genetry Solar Posted February 12, 2021 Share Posted February 12, 2021 This is undoubtedly a very sensitive topic for some, especially those who may have heard about "making yourself a large battery for very cheap." Please note that we at Genetry Solar do not condone or recommend these types of projects, largely in part due to the severe potential risks that could result in burning your entire house down. (Sid) I have personally made a "DIY powerwall" myself out of recycled laptop batteries. 14S, 26P or something like that--over 360 cells. Made a nice 50Ah battery for an eBike. However, in the process of making the battery bank, I did discover that there are a wide range of cell problems amongst 18650 Li-Ion batteries: "Dead" cells (< 2.0v) can sometimes be "rejuvenated" by low charging current. Sometimes these cells end up with good capacity. Sometimes they will be a dead short...other times they'll have a significant self-discharge rate. "Heaters" are cells with extremely high self-discharge rates, and they are literally ticking time bombs before they overheat and explode burning lithium all over the place, catching any nearby items on fire. One cell I encountered charged perfectly fine up to 4.1v (2.2Ah capacity, too--it was a good one!) but any attempt to take it above 4.1v resulted in the cell getting hot to the touch. Unknowingly mixing a cell like this into a bank that is then charged to 4.2v is literally asking for a fire. Cells with a lower self-discharge rate are already "sick", and likely will only get worse as time goes on. "Cell level fuses" provide absolutely no protection against "heater" cells, as their self-discharge current is often less than the 1C rating (i.e. 2.2A current for a 2.2Ah cell). They only protect against cells that instantly fail to a dead short...which I have never experienced. In the end, I ended up "parking" the eBike (got a car, haha!) Two years later, my DIY "powerwall" bank had 3 completely dead strings resulting from excessive self-discharge of "iffy" cells that had tested >2.0Ah in capacity checks. A house fire is nothing funny. Not worth saving a few bucks to "make it yourself." If you're set on making a DIY 18650 powerwall...all the more power to you, but please note that we will not provide help for projects of this sort. We're here to try to help people realize their off-grid dreams safely...not lose our shirt due to liability. Personally, I recommend Lithium Iron Phosphate batteries (also referred to as LiFePo4, LFP). They are a much safer technology, with somewhat lower energy density...but the safety is worth it. My DIY 32650 12kwh LiFePo4 bank on my off-grid system has been an absolute dream--zero maintenance, no issues whatsoever. (Made with new old stock cells.) It helps to price shop around, as most commercial solutions are prohibitively expensive. But that's a topic for another thread. 2 Quote Link to comment Share on other sites More sharing options...
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