Stored at 28v! - 24V 58.8ah 1.35kWh LIFEPO4 A123 MODULE 7s
Please read this item description as to why these modules are only $20.
These A123 modules came out of an EV pack where we usually get the $200 modules out of. This pack in particular had a failed BMS and instead of this pack being charged to 25.55v per module (3.65v/cell) it was charged to 28v per module (4v per cell). Now, lifepo4 cells can safely be charged up to 0.7v above fully charged. Here is where this gets interesting, especially from a watt hour and energy density standpoint. These modules were charged up to 28v and left there for 6 months. When we discharged the module the first time we got 65ah (above the 58.8ah when new). The discharge curve, instead of the hard hold at 3.2-3.3v the curve was now around 3.7v before it dipped off. When we cycled the module from 2.5-3.65v per cell we got 25ah, when we cycled the battery from 2.85-4v per cell (the same voltage range as a normal lifepo4 module) we got 105% capacity (61ah). The battery discharge curve looks exactly like the other A123 modules that were never overcharged, however these seem to have taken a higher nominal voltage characteristic and what's more interesting is the cells stayed balanced within .002v throughout every cycle. I don't know if maybe this has been studied or how this would ultimately impact the cycle life, but this battery module which was 1.36kWh at 3.3v nominal per cell is now testing at 1.58kWh at 3.7v nominal when charged back up to 4v per cell. Which is a 14% increase in watt hours or energy.
Now as far as you purchasing these modules, at just $20 we're basically giving them away. I would not recommend using these and charging them up to 4v per cell. You should charge up to 3.65v per cell with a bms like normal lifepo4. However if you want to test this theory go ahead.
To be clear these are 7s lifepo4 modules that were 58.8ah, they test at 25ah when cycled within normal lifepo4 range but test full capacity when cycled up to 4v instead of 3.65v per cell. Or 28v per module instead of 25.55v per module.
The 5th photo shows the cycle curve chart when we cycled this within 2.5-3.65v per cell. As you can see the curve starts to level out around 3.65v just like it should at 3.2-3.3v per cell.
Balance connector is included. There are 10 wires. 8 for balance and 2 for the temp probe. This pack is built to last and it uses the highest quality A123 cells so you can expect these to last for a very long time.
Module Dimensions: 8.75" x 6.5" x 9.75"
Module Weight 27.13 lbs
Nominal Voltage: 23.1 (7 cells, 3.3v per cell)
Maximum Charge Voltage: 25.55 (3.65v per cell)
Maximum Discharge Voltage: 17.5 (2.5v per cell)
Recommended max charge rate: 117a (2700w) (2c)
Recommended max discharge rate: 176a (4000w) (3c)