Lithium Iron Phosphate

[SeagullOne]

Anyone have any experience with lithium Iron Phosphate batteries?

I've been outright refusing to use batteries with lithium chemistry, but the lithium iron phosphate batteries at all battery dot com sound pretty safe, according to their specs (without being careless of course). They are looking extremely attractive for some of the projects I have in mind.

For instance, I'm thinking of having NINA run via a mini ITX motherboards with an ION GPU. I set up four 3.2V 8AH lithium iron phosphate batteries in parallel for 12.8 volts, run it through a DC to DC converter hooked up to the ITX motherboard with a switch and a fuse, and Bam, I've got mobile computer system for NINA with a small profile and a power supply that weighs nothing compared to nimh battery packs.

Also, a couple of these would seem like a fantastic application for a biped of sorts....hmmm...
http://www.all-battery.com/32v20ahlifepo4lithiumironphosphaterechargeablebattery.aspx

[VegaObscura]

I set up four 3.2V 8AH lithium iron phosphate batteries in parallel for 12.8 volts

Four 3.2V batteries in parallel will not give you 12.8 volts.  It gives you 3.2 volts with four times the capacity.  Connecting four 3.2V batteries in series will give you 12.8 volts.

[Soeren]

Hi,

I've been outright refusing to use batteries with lithium chemistry, [...]

I take it that you have no cellular phone, no PDA, no new powertools etc. then?   

A car can be extremely dangerous... If there's an idiot behind the wheel.
A bread knife can be extremely dangerous... If the one holding it is a psychopat.
A lithium battery can be a bit dangerous... If you are careless and give a damn about proper charge/discharge techniques.

I have used lithium batteries for a vast range of apps during a decade+ and so has my friends and coworkers and neither them nor I have experienced even a single cell catching fire (yet, at least).

Staying within the manufacturers nominal parameters is the key - don't let horror stories scare you off of the benefits lithium technology brings. With millions of Lithiums in use every day and only a few verified stories about lithium "explosions", I'd say it's much more dangerous to drive a car (even if you leave the idiot out of the equation).

The important things to keep in mind with lithiums are... Charge current, end-of-charge voltage, discharge current, end-of-discharge voltage and cell temperature. Keep within manufacturers specs and you have a lightweight power source.
And don't open them of course!!

The Iron Lithiums are considered the safest (although some will surely translate this to "can be treated worse"), but are a bit heavier per capacity (nothing like Nickel based cells though).

[SeagullOne]

Four 3.2V batteries in parallel will not give you 12.8 volts.  It gives you 3.2 volts with four times the capacity.  Connecting four 3.2V batteries in series will give you 12.8 volts.

Oh yeah, right... 
I meant series.

Your advice is very encouraging, also, Soeren. I'm anxious to try these batteries out.

[waltr]

To add:
 There are many nice little Lithium charge controller chips made by a number of manufactures. These take care of ensuring the charge conditions are correct and switching charge states on the correct condition. A search on the web sites of Microchip, Linear Tech, Analog Devices, Maxium, National Semiconductor, Texas Instruments and others will find these.

I started using LiPo batteries on my latest Bot and have been thrilled with the performance. These batteries took up a lot less space, are lighter and have a larger capacity than the NiCd or NiMH batteries I previously used. I built in a charger using an MCP73841 chip that makes charging easy and safe.