This thread is not EV related, but its battery related, so I figured its not entirely out of place.
In my quest to erase Lead Acid technology from my life I am working on upgrade of my home UPSs to LiFePO4 batteries. Brief power blackouts and brownouts are not uncommon in my area, so I try to protect my electronics investment with small UPSs of various sizes strategically located around the house
. Since power loss is usually brief, few seconds to few minutes, I am not interested in large expensive whole house UPS, I have a gas generator I can use in case of real emergency, so the focus here is on small, computer type, UPSs you can get at any retail outlet. They are rated by their power level and come with sealed LA batteries of various capacity and voltages of 6V, 12V or 24V. Usually LA batteries in these units are capable of just a few minutes of max power output and have limited life span. I typically end up replacing UPS batteries every 2-3 years, which I find to be a waste of money, hence this project.
As most of you know, 4 LiFePo4 cells in series have nominal voltage of 12.8V, which happens to be in the same range of 12V LA battery. This makes it very easy and convenient to swap LA batteries with LFP batteries. In this project I need small capacity cells and 2C-3C rates, so UPS can run for 20-30 minutes. Obviously prismatics are too large for this purpose and even Headway cylindricals are too big for most small UPSs, so I went on Ebay looking for cells in 1-3AH size range. Oh boy, plenty of choices, most direct from China, some are individual cells, some are pre-assembled packs of various P and S configurations. I am cheap and handy enough to build my own 4 cell pack
, so I am only looking for individual cells. Auctions offering genuine A123 cells
get my attention
. I can't resist to pay $10 including shipping for 4 1.1AH genuine A123 cells
. Here is the seller.
They offer variety of tab options, since I am not interested to spot weld my own tabs, I pay $.80 more to get tabs added.
Despite the holiday season, my cells arrived in less than 2 weeks, much sooner than I expected. Nicely packed, tabs as ordered, kudos to this seller, he is doing a great job so far. All cells at exactly 3.3V.
I whip out my trusted single cell LiFePo4 6A charger and within few minutes all cells are at 3.65V. They arrived at about 75% SOC based on my charge current/time measurements. Now they are 100% SOC and top balanced. I drilled tabs, so I can use #4 bolts to assemble them in series.
Now I have a 1.1AH 12V LiFePO4 battery that cost me $10 and looks like something terrorists in movies cobble up to blow stuff up
My smallest 325VA UPS which powers my Internet/VOIP/WLAN and has to fit inside of a small in-wall wiring cabinet died recently, so a trip to CompUSA and $35 later ( they had a good sale on $50 ULTRA model which is small enough to fit my cabinet ) I have a new UPS to boot.
I am disappointed that new UPS has 6V battery, not 12V as my old one had. So, I take apart my newly assembled battery and reconfigure it from 1P4S to 2P2S. Same energy capacity, just different V vs A ratio to match the UPS.
Bingo, UPS comes alive and kicking. I measured my load on this UPS to be around 20Watt, the battery is 2.2AH*6.4V = 14WH, so it will survive up to 40 minutes power outage, which is at least twice as much as the LA battery would do. Best part, this LFP battery will outlast the life of UPS and possible the house its in
, so no more replacements, woohoo!