RE: Even more homebuilt charger madness

[Rod.Hower@ametek.com]

Here's some info on the patent for inquiring minds.
It is patent #6,181,106
Go to http://patft.uspto.gov/netahtml/srchnum.htm
and type in the patent number to see the full description
Rod

TECHNICAL FIELD

The present invention relates to battery charging generally and, more
particularly, but not by way of limitation, to novel means and method for
sequentially charging battery cells or cell banks using a high rate of
current.

BACKGROUND ART

The rapid charging of batteries, and in particular lead-acid batteries, has
been pursued for decades. Procedures for rapid charging of batteries have
been reported over the past 20 years or so, mainly for Ni--Cd batteries
and, to a lesser extent, for lead-acid batteries. Interest in the latter
has increased lately because of intensified interest in electric street
vehicles.

All properly designed batteries contain more active material in their
plates than their ratings would indicate. In spite of this, most secondary
(rechargeable) batteries, especially lead-acid batteries, are routinely
used to only about 80 percent of their ratings. Even though only about 80
percent of rated capacity is extracted, the cycle life and lifetime energy
throughput is significantly reduced from that of shallower discharges. The
cycle life and lifetime energy throughput at 100 percent depth-of-discharge
is typically very low.

Conventional charging techniques coupled with rigorous standard discharge
conditions often yield a significant amount of cycle-to-cycle capacity
variation. Furthermore, grain structure of the active plate material
becomes worse and worse with each charging cycle.

A significant amount of research has recently focused on high-rate
charging, primarily for rapid recharge (usually partial recharge) for
extended range or emergency conditions in street electric vehicles. Until
recently, battery charging designers followed the "ampere-hour rule" which
holds that the rate of recharge current at any point in the charging cycle
should equal the number of ampere hours to be recharged. In spite of this
"rule," remarkable side benefits have emerged from studies of high-rate
charging--that is, charging rates greatly in excess of that prescribed by
the "ampere-hour rule." It appears from the results of these studies that
high-rate charging permits greater utilization of active plate material
which allows greater depths-of-discharge without detrimental effects and,
in fact, is often accompanied by significantly greater cycle life and
lifetime energy throughput.

Preliminary physical analyses of high-rate charging effects show: (1)
improved maintenance of optimum crystal size within the plate structure,
(2) better penetration or use of depth into the third dimension of active
plate material, (3) increased electrolyte stirring and convection within
local regions and throughout the plate and electrolyte reservoir channels,
and (4) enhanced nucleation for crystal formation in deficient plate
regions.

Conventional high-rate charging has an objective charging a battery in a
small fraction of the time required for conventional charging, through the
application of a high rate of current in parallel to all battery cells or
cell blocks. Accordingly, a primary drawback of conventional high-rate
charging is the extremely high power inputs required. For example, a
charger might require 5 kilowatts (220 VAC@23 amperes) during the early
part of the charging cycle for conventional charging, but could easily
require 50 to 100 kilowatts (440 VAC@113 to 228 amperes) for high-rate
charging. Another problem with conventional high-rate charging techniques,
which affects battery life, is the inevitable polarization and its
concomitant voltage gradients and overvoltages, which usually requires
periodic equalization between cells or cell banks. Ideally, some form of
equalization should occur during each recharge, but this is usually
impractical. Further problems with conventional high-rate charging are a
high rate of temperat
ure increase and the possibility of dangerous pressure increase.

Accordingly, it is a principal object of the present invention to provide
means and method for high-rate charging that do not necessarily require
exceeding the maximum power requirements of conventional (i.e., not
high-rate) charging methods.

It is a further object of the invention to provide such means and method
that can permit complete charging in less time than conventional charging
techniques.

It is an additional object of the invention to provide such means and
method that permit utilization of a greater percentage of rated battery
capacity, ideally 100 percent of a well designed battery.

It is another object of the invention to provide such means and method that
increase cycle life and lifetime energy throughput, to perhaps a doubling
or tripling of cycle life and lifetime energy throughput.

A further object of the invention is to provide such means and method which
performs equalization (cell-by-cell or block-by-block) during each
recharge.

An additional object of the invention is to provide such means and method
that improve overall charge coulombic efficiency from, say, 90 percent for
conventional charging to greater than 95 percent.

Another object of the invention is to provide such means and method that
optimize and synchronize the battery state-of-charge computer employed.

Yet a further object of the invention is to provide such means and method
that provide alerts concerning abnormalities, especially equalization
imbalance.

Other objects of the present invention, as well as particular features,
elements, and advantages thereof, will be elucidated in, or be apparent
from, the following description and the accompanying drawing figures.

DISCLOSURE OF INVENTION

The present invention achieves the above objects, among others, by
providing, in a preferred embodiment, a sequential high-rate battery
charger for charging a battery having a plurality of cell units, said
battery charger comprising: a high current source; means to selectively
sequentially connect each of said plurality of cell units to said high
current source; and means to sequentially provide high current from said
high current source to said each of said plurality of cell units for a
first selected period of time.