Improvements in and relating to Methods for Charging and Discharging Accumulators.
Year: 1899

page_text: Date of Application, 8th Mar., 1899-Accepted, 8th Mar., 1900
COMPLETE SPECIFICATION.
Improvements in and relating to Methods for Charging and
Discharging Accumulators.
We, VIVIAN BOLTON DOUGLAS COOPER, of Broadway House, The Broadway, in
the City of Westminster, and EUSTACE RIDLEY, of 53, Charterhouse Street, in the
City of London, both in the County of Middlesex, Electrical Engineers, do hereby.
declare the nature of this invention and in what manner the same is to be
performed to be particularly described and ascertained in and by the following
statement:
This invention relates to improvements in the methods of charging secondary
batteries and has for its object the simplification of the switching gear and the
economical and efficient use of batteries without the employment of regulating
cells.
In the ordinary method of charging secondary batteries a dynamo is used
capable of going to about 24 volts per cell and the cells of the battery are charged
in series whilst in discharging, by means of multiple contact switches, the
number of cells is varied to maintain an equal pressure. during the whole
discharge. The result is that the end or regulating cells are charged and dis-
charged differently to the other cells with the result that they rapidly deteriorate
and their capacity is never fully utilized.
1
In a modified method of charging from the omnibus bars of a supply station,
the pressure of the bars is added to by means of a subsidiary dynamo or booster,
which may be driven by a steam engine or preferably by a motor taking power
from the mains.
Our invention consists in an extension of the use of such a motor generator so
that whilst the motor generator is used to raise the omnibus bar pressure to that
required to charge the cells during the period of charging the same motor
generator with the same connections and running in the same direction is used in
discharging with its functions reversed, the booster now running as a motor
and absorbing the extra pressure of the battery in driving the motor as a dynamo
so that current flows from both armatures to the bus bars at the required pressure."
Thus all the cells are equally charged and discharged the power wasted is reduced
to a minimum. the useful discharge capacity is increased and in the event of
a short circuit an excessive discharge is prevented by the opposing E.M.F. of
the booster.
In order to carry this invention into effect, there are in general two methods
which we adopt. In the first of these the regulation is by hand, in the second*
of these it is automatic. In the system for regulating by hand a shunt or
separately excited motor is connected to the omnibus bars and has in the circuit-
of the magnetizing coils a resistance, by the regulation of which the speed of the
motor may be controlled. Coupled to this motor by means of a belt or direct by
a shaft is a generator capable of giving a pressure equal to the maximum excess
of pressure over that given by the omnibus bars required to charge the battery.

page_text: The field windings of this machine are also connected to the bus bars and
provided with a resistance in circuit by means of which the pressure can be
regulated.
In working the following is the procedure:-To charge the battery the motor
is started driving the generator, the pressure of the generator being, regulated
until the charging current reaches the required value. To discharge the battery
the strength of the motor field is reduced by means of a resistance in the
magnetizing circuit until the current ceases to flow through the booster armature
into the battery. Continuing this regulation and assisting it when necessary with
resistance in the booster magnetizing circuit, the battery will commence to
discharge. The generator now becomes a motor and the motor generator
delivering power at the omnibus bar pressure to the omnibus bars.
In the automatic method of regulating, the arrangement is the same with this
exception, that the machine for raising the pressure from the omnibus bars to that
required by the battery has a very small separate exciting winding, and depends
mainly for its excitation on an independent winding composed of two coils
arranged in opposition, one of them being connected across the main between the
ommibus bars, the other being connected across the terminals of the battery and
the resultant magnetizing effect depending on their difference, that is on the
difference between the accumulator and the omnibus bar pressure
The same effect may be produced by arranging a winding so that it is connected
to the similar poles respectively of the omnibus bars and the battery, the current
through it then depending on the difference of pressure between them.
The effect of this arrangement is that the E.M.F. of the dynanio is a small
constant quantity which is the amount necessary to pass the current through the
battery against the resistance only plus an amount proportional to the difference
between the omnibus bar pressure and the battery pressure, which is the amount
required to overcome the E.M.E. of the battery. In this arrangement therefore
the only variable is the speed of the machine which acts as a motor during
charging. By raising this speed the battery will be charged. by lowering it the
battery will be discharged both of which can be effected by adjusting the regulator
of this machine. It is necessary also in this arrangement to reverse the direction
of the current in the shunt winding for charge and discharge.
In the case of two or more batteries being used on independent circuits, or our
a three or multiple wire system of distribution, one motor would be used to
drive a number of boosters one for each secondary battery, while charging. By
adjusting the resistances in the existing circuits of the motor and booster fields,
it will be possible to discharge one or more of the batteries through their respec-
tive boosters, the power thus derived being used either to assist the motor or to
drive it as a generator as in the preceding examples.
Although the machines in the foregoing examples are all described with
separately excited field magnets we may in addition use series of windings where
they would be of advantage.
In connection with the foregoing arrangements, and to allow of an extra high
discharging current we provide in shunt a heavy resistance through which part
of the current may flow, the remainder as before Howing througli and driving the
booster armature. This resistance may be automatically thrown in or out of
circuit by an electro-magnetic or other device operated by the discharging
current or operated by hand, as an alternative, a switch operated either auto-
matically or by hand can be provided for cutting out the booster altogether and
enabling the entire discharge of the battery to be put on the bus bars either
directly or through an adjustable resistance.
In order that our invention may be better understood, it is illustrated by
Figures 1 and 2 which shew in diagram form these two arrangements.
In Figure 1, a, b, are the omnibus bars having connected dynamos c, d, e.
A is the armature of the motor and B the armature of the booster. K is the
secondary battery. is the shunt winding and r the shunt resistance of the

page_text: generator. A, and sand are the shunt windings and resistances of the
booster B, which are connected respectively to the accumulators K and to the
omnibus bars as shewn, and the working is as already described. In Figure 2
which shews the method of connection for the automatic regulation. A is the
armature of the motor and B the armature of the booster. ab, as before are
the omnibus bars having connected dynamos, c, d, c. K is the accumulator.
s, r. are the shunt or separate exciting winding and resistance of the motor
whilst mare the windings connected respectively to the omnibus bars a, b, and
the accumulator, being wound in opposition, s is a small separate exciting
winding which may have the resistance connected with it. The method of
operating has already been described.
In the case where two coils only are used say the coil m instead of being con-
nected too would be connected to the coil » being disconnected or dispensed
with, and the exciting current is then proportional to the difference of pressure
between the omnibus bars and the battery.
Figure shews how the motor and booster armatures would be connected to
two batteries working one on each side of a three wire system. A as before is
the motor armature connected to the outer conductors of the system; &,,, are
the bus bars. B and B are the boosters all three armatures being on the same
shaft. The magnetising coils are not shown here but as before are under
independent control. This arrangement could be extended for use on a 5 wire
system.
Figure 4 shows the heavy adjustable resistance which we provide to allow of a
greater discharge than would be conveniently carried by the booster B. This
resistance T is thrown in or out of circuit by the switch V and will carry part
of the discharging current, the booster B carrying the remainder; or if the booster
be disconnected T will be capable of carrying the entire current.
It will be seen that our invention not only simplifies the switching gear and
enables the batteries to be used more economically and efficiently without the
employment of regulating cells but it also prevents the excessive discharge of
the battery.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that
what we claim is:--
(1) In combination with a secondary battery a motor connected to the omnibus
bars or source of supply and driving a generator or booster to raise the pressure
with resistances in the exciting circuits respectively so arranged that by adjust-
ment of the resistances the battery may discharge through the booster driving the
same as a motor and delivering, energy to the source of supply substantially
as described and illustrated.
(2) In combination with two or more secondary batteries connected to inde-
pendent circuits or the multiple wires of a three or multiple wire system of
distribution, a motor connected to the omnibus bars or source of supply driving
two or more generators or boosters to raise the pressure with resistances in the
exciting circuits respectively arranged so that by adjustment of the resistances
either or any of the batteries may discharge through their respective boosters
driving the generator as a motor and delivering energy to the source of supply
substantially as described. and illustrated.
(3) In combination with a battery of accumulators and a motor as claimed in
Claims 1 and 2 a motor generator or booster having differentially wound exciting
windings or a winding differentially connected and so connected to the source of
supply and the accumulators that the E.M.. depends on the difference of pressure
between the accumulators and the source of supply substantially as described and
illustrated.
(4) The combination with the motors, generators and circuits claimed in
Claims 1, 2 and 3 of a switch or switches automatic or otherwise and a resistance

page_text: or resistances for cutting out or shunting the booster armature so as to allow of
a. abnormally heavy discharge substantially as described.
(5) The arrangement of circuits, batteries, dynamos and motors described and
illustrated in Figures 1, 2 and 3.
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1004
ROBERT E. PHILLIPS, Assoc. M.Inst.C.E., M.I.Mech.E.,
Chartered Patent Agent, 70, Chancery Lane, London, W.C.,
Agent for the Applicants.