The members of this list have an amazing
technical breadth.  Knowing that some here
are dumpster divers like myself, I hope I
may pick your brains, and maybe uncover
cheap ways to make high current switchers.

I need to make a charger for deep cycle
flooded cell lead acid batteries for a battery
back up application.  I only need to make one,
and one goal for this project is low cost.  I
intend to automate operation of the charger
with a PIC.  I will implement the preferred
charging cycle by sensing a good battery,
applying a current limited charge (the bulk
charge phase), followed by a temperature
dependant voltage regulated charge (the
absorption phase), and finally ending with a
lower temp dependant float phase to maintain
the battery.  I expect the supply will need
to produce 10-15A over a 12V to 15.5V adjustable
range to work over the expected temp range.

I reclaimed from a dumpster a beautiful Telcom
power supply made by SOLA. It uses a ferroresonant
(constant voltage) transformer to condition
the power from power line garbage and provide
very good voltage regulation.  It also has mammoth
caps and a 5lb choke to yield clean DC.  Because
ferroresonant transformers like this do not
appreciate loads with a high harmonic content - I
can't use something like SCR's on the unfiltered
DC from the rectifiers - I need to tap the power
at the filtered DC output.

I can either use an ugly and horribly inefficient
linear regulator, or attempt a switch mode supply.
I've done small switch mode supplies, but never
anything over an amp.  Say I were to obtain a suitable
inductor and maybe diodes from a bad PC power supply
(say the 3.3V high current leg).  Does anyone have a
favorite easy to use buck controller that could
effectively utilize the reclaimed inductor?  What do
I look for in a MOSFET?  Any non-obvious caveats on
high current supplies?  I plan on  putting a
crowbar overvoltage protection circuit on because
if the MOSFET decided to fail shorted
it could be disastrous.  Thanks in advance for
your thoughts!



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