Re: VERY BAD BOY charger (50KW)

[LEE A HART <XURQ03A@PRODIGY.COM>]

The idea is sound, though the devil is in the details. (and, boy are there
some details! :-)

>Phase one) Connect 120V pack to a Curtis 1221B controller.
>Run the OUTPUT of the Curtis to the 84V Optima pack.

A controller is designed to drive an inductive load, like a motor. If you
use it directly to charge batteries, the current rises instantly each time
its transistors turn on, instead of gradually when there is motor
inductance. Thus the controller is exposed to exceptionally high peak
currents, which its current limit is unable to properly limit.

You need to be *very* sure not to charge batteries at high current when
they are nearly full charged. If even one cell hits full charge with high
current still flowing, then it will be converting 100% of the energy
applied into gassing and heat. 2.5v at 100amps = 2500 watts! In a matter of
minutes that cell will be spouting geysers of boiling acid!

To make this work, add an inductor in series with the controller's output.
And be sure to limit charging current as you near full charge.

>Phase 2) Get a bunch of BIG diodes and make a full wave bridge...
>Run the rectified AC into the Curtis 1221 controller...

Controllers have a set of filter capacitors on their input. They are
intended to handle the ripple with DC on the input. The ripple voltage is
at most a few volts.

They are *not* designed to handle the ripple from a rectifier on the power
line, which is 170 volts peak-to-peak on 120vac (double this on 240vac).

Likewise, the controller isn't designed to withstand the 170vdc peak it
will see, or operate correctly when its input voltage is swinging wildly up
and down 120 times per second.

And of course, controllers aren't built to withstand powerline noise, which
routinely exceeds 1000v peak, and can be over 6000v during thunderstorms.

To make this scheme work, you would need a transformer for isolation and to
step down the voltage so peaks don't exceed the controller's rating. And a
much bigger set of filter capacitors to keep the ripple down to something
like 10% peak-to-peak.

The previous caveats apply to restricting charging current near full charge.

Lee Hart                     If you would not be forgotten
4209 France Ave. N.          Soon as you are dead and rotten
Robbinsdale, MN 55422 USA    Either write things worth the reading
phone (612) 533-3226         Or do things worthy of the writing
e-mail XURQ03A@prodigy.com   (Ben Franklin, Poor Richard's Almanac)
Re: VERY BAD BOY charger (50KW)