Instructables

LiFePO4 (3.2V) project, within a 3 x AA battery holder!

Picture of LiFePO4 (3.2V) project, within a 3 x AA battery holder!
Thinking "inside the box" ? Check this novel electronic project case, which is formed from a partially gutted 3 x AA cell switched battery holder !  Circuitry is mounted on a sliced solderless breadboard, while a "Kiwi Board" layout suits a final soldered version.  Power is via a single 3.2 V  LiFePO4 (Lithium Iron Phospate)  AA sized rechargeable cell.  Yes - just one cell- do away with multiple cells and their associated matching,aging,charging, housing, connection & terminal contact woes !

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

 


 
 
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Step 1: LiFePO4 ("LFP") rechargeable cell features

Picture of LiFePO4 (

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).

manuka (author) 3 months ago
The Feb. 2014 "Silicon Chip" monthly intends an article on this "boxed" approach, with a magnificent cartoon by Barney "Ohm-art" Walker to set the tone. When trimmed to a 20 x 10 hole array, Jaycar' s HP9588 board has shown itself very well suited for many breadboard developed circuits - PICAXE, 555, logic & of course "DANDY" (Discretes Are Not Dead Yet).

To help cash strapped hobbyists or schools who are unable to justify LiFePO4 cells, 4 x AA battery boxes can be converted. These allow 2 x normal 1.5V alkalines to be used.
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manuka (author) 5 days ago

A new board released by Australian firm Protostack seems
far superior to Jaycar's Paxolin versions. It's professional looking but
cheaper (Aust $2.90 ), in fibreglass, silk screened, and with PTH (
plated thru' holes).

See => www.protostack.com/boards/prototyping/prototyping-board-small-style-1

PB-GE-S1_LRG.jpg
manuka (author) 5 months ago
Update: Further variations with 2 and 4 switched battery boxes have now been developed. An appealing feature of the 4 AA box is that 2 regular AA alkalines can be used (2 x 1.5 -3V) if LiFePO4 are unavailable. Some of the board slices used are fibreglass based KPB (Kiwi Patch Board), but this gets costly for small versions - it's wasteful to slice & dice a nifty KPB for trivial needs!

For skinflints & schools I've hence also considered Australian/NZ firm Jaycar's (www.jaycar.com.au) HP9556 & HP9558 (Paxolin) boards, which can yield up to 5-10 board "fingers" from a single ~$3-$5 purchase. When deeply scored on both sides they'll crack apart nicely, & rough edges can be quickly sanded smooth. A quick spray of clear protective coating prevents track tarnishing & aids soldering nicely.

Sure - the resulting boxed board is not that profesional,but it's logical/neat/cheap/quick & it's compact layout alerts assemblers to today's tight circuitry.
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manuka (author)  manuka3 months ago
Jaycar, the popular Aus/NZ electronics outlet, now stock  AA sized 14500 rechargeable Lithium cells. However they're in the Aust $10 range, and no simple USB smart chargers (nor dummy cells) are yet handled ...
3.7V  Li-ion       =  Jaycar code SB2303
3.2V  LiFePO4 =  Jaycar code SB2305

LiFePO4 imports from China/Hong Kong are probably still possible at far lower prices, but Boeing's "Dreamliner" battery woes has meant that international air freighting of Li cells (especially Li-Po) has recently become "difficult".
manuka (author) 11 months ago
Modest blush -glad you liked it! If the hype pans out I see LiFePO4 cells/batteries being near revolutionary, & AA sized ones being a great way to explore features.
Granzeier11 months ago
Wow! When I first saw this 'ible (peppered with "More Text To Come"), I thought it was a pretty cool idea. Now that you have fleshed it out with (LOTS) more text and additional pictures, I really love it. Nice job.
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