I'm working on a project Powered by 2 LiFePO4 batteries,  4S 10AH each
battery (2 4S batteries instead of 1 8S just for mounting/enclosure
purposes) , and I'm working on a balancing mechanism/method

I found this article
http://www.ifrsys.com/ams/pagesproduct/presentations/NASABatteryWorkshop200=
7AeroflexBEU.pdf
 See slide 9 for an rough diagram.    Except rather than individual
transformer and a common bus for everything, I want to wind 5 windings
on a core, have 1 hooked to each cell in the battery unit, an have a
common bus available for balancing between packs(or to a peak detector
and check the voltage on each cell if you can trigger each FET
individually) . I like the simplicity of a the design,  a
transformer, mosfets which acts as a synchronous rectifier when needed
to, and an oscillator to wiggle the gates as needed.

I havent done much with making my own magnetics in the past, other
then throwing some turns on a random ferrite to make an inductor to
kill some spikes.  For battery balancing this is obviously going to be
operating in a transformer mode instead of a mutual inductor/flyback
sort of device, with tight voltage coupling between windings, which
leads me to think that I'll need the following properties
Low Parasitic inductance/magnetizing current
High permeability core to provide above
30k-100khz or so operating frequency of the device, so "good"
permeability higher then that. (How many odd harmonics up from the
main frequency should the ferrite still have a relatively high
permeability for?)
Space between curves on B-H curve should be small for low energy
storage/inductance.

So I'd be looking for a core of something like Fair-Rite 75,76 or 77?
http://www.fair-rite.com/newfair/materials.htm  Link to fair-rite's
materials page.

Finally,
The turns should be put on in parallel rather than wound individually
( http://wiki.4hv.org/index.php/File:GDTWinding.png )  for the best
coupling/lowest inductance?  Amidon ( http://www.amidoncorp.com )
seems to have plenty of stock/variety so most likely I'll be picking
up supplies from them.

Thanks for any help/guidance/thoughts!

--=20
Jonathan Hallameyer
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