Reasonably Good Charging Algorithm?

["Arthur Matteson" <fanofca@hotmail.com>]

This has probably been said a few times, but I'd like an overview of what my battery charger should do.  I'm concerned about my
batteries' range and life, especially since my favorite gel cell recently had a slow and torchered death.  I'm also concerned about
overcharging and gassing since I've apparently done it more often than equalizing should be done.  I've heard of slowing down the
last 20%, and Lee Hart's 2% rule, but I'm not sure what a good balance between reliability and time is.  I'm basically aiming for a
simple 8 hour charge, but quicker is better.

I (will) have eight DieHard 12V Marine batteries in series at first, for 96V, and I am considering 120V and 144V setups also.  I
have to make a confession -- I bought two different types of batteries.  I have two of the 115Ah and two of the 105Ah.  I got the
first ones as a pair, aiming for more range, but they were out of stock the second time I went to pick up a pair (Sears).  I
actually prefer the 115Ahs because they have less complicated terminals and aren't any bigger or heavier.  I still have to buy at
least four more.  What do you all recommend I do?

The charger will be isolated, and I'm planning on putting in PFC if I can get it to work.  The power level is not impressive,
however.  The only allowable input is 120VAC.  The charger will max-out a normal 15A outlet, i.e. 1700-1800W output.  I'd like to
use as much of it as I can.  In order to build the power supply, I need to know the highest voltage that will be across the battery
packs (the secondary will have taps to switch between, since you don't change pack voltages that often.)  Is 15V OK?  I use a buck
converter to bring down the voltage to what I want, and I will monitor current with an induced flux (?) sensor.  All Electronics has
some good ones: http://www.allelectronics.com/cgi-bin/category.cgi?category=395&item=VT-3&type=store   I should have one arriving on
Friday, it's what I'm planning to use to sense current.

I also would like to know the procedures for charging from different discharged levels.  (Does the "first 10%" mean the first 10% of
the battery capacity, or only of what was discharged?)  I would like to have the option for equalizing -- or do you not recommend
it?  In order to know how much has been drained out of the battery, I'm planning on integrating power with respect to time to find
energy.

I also may choose to take the Peukert effect into account, by having a memory space that stores how much recoverable energy has been
used.  I say recoverable since it will come back if you leave the car sit for a while, right?  How on earth would I tell how
much...I guess that's what experimentation is for...  Could I stick in the pack voltage to the equation to narrow down/zoom in on
the estimated current range remaining?  It would be nice to have the range remaining bargraph rise up a few minutes after a large
drain.

The charger will contain a balancer.  It is fairly simple -- it has 24 relays that switch one of two resistors (5 or 8 ohm) across
each battery.  The resistors can be disabled, and the voltages across each battery can be read with a 24-bit A/D in both states.  I
am planning on only running this utillity while the charger is on, but changes are okay.  What's the best time to balance, and how
much is acceptable?  1, 2, 5A?

But first things first.  I seem to get carried away with the extras a lot...  : )   Any recommendations or suggestions are also
welcome.  Thanks in advance; this is a great list.

Arthur Matteson
-- '80 Lectric Leopard
-- Homebrew induction drive (soon)
-- Ann Arbor, Michigan
http://www.cardomain.com/id/art4evs

P.S.: Where's Madman lately?  I'm sure he knows a lot about PFC and charging algorithms.  : D