This 24 step Instructable covers -
* LiFePO4 cell features & cautions
* Battery box basics
* Partial gutting of a 3 x AA battery box
* Solderless breadboard etc options
* Railed breadboard slicing.
* Circuitry to suit
Step 1: LiFePO4 ("LFP") rechargeable cell features
LFP batteries are still quite new & their long term features have yet to be fully verified, but their claimed characteristics include –
* An output of ~3.2 V, which remains quite steady under load, only falling in the last 5% of capacity (Li-Ion starts near 4.2V but falls progressively to ~2.7V, while Lead acid is nominally 2V, and NiCd/NiMH is only 1.2V)
* Lightweight and compact – extremely good power to weight ratio (appealing for motorcycles etc)
* Require constant current (CC) charging, which then tapers off as 3.6V constant voltage (CV) is reached. Note –LiFePO4 cell voltage settles back after full charging to ~3.3V, with 3.2V being the usual quoted value
* A specialized (but cheap) charger should be used, although simpler approaches may suffice in a pinch (providing LFP charging needs are respected !).
* No memory effect – cells can be charged/discharged at any state.
* Extremely low standby losses.
* Modest but appealing Ah (Amp Hour) capacity (but lower than comparable Li-Ions)
* A cycle life of several 1000 times (and far greater than Li-Ion’s annoying and costly 100s)
* Can be near fully discharged (although 2.5V is the recommend cutoff), but will probably be ruined if totally flattened.
* High charge (~1C) and discharge (~10C) –both rates however lower than comparable Li-Ions. ( “C” refers to the capacity in Ah, with 700mAh being 1C for that AA cell type)
* Quite safe for all discharge applications, as the cathode is non flammable and stable. No lithium remains in the cathode of a fully charged LFP cell.
* Excellent sub-zero and elevated temperature performance.
* Environmentally benign (“green”) in manufacture, usage and disposal -no hazardous internal contents.
* Capable of even further performance enhancement when doped with Yttrium (Y -pronounced “it-tree-um” and a common element- found apparently in cabbages!). Such cells are titled LiFeYPO4 (LFYP).