ACCUMULATORS. STORAGE OR SECONDARY BATTERIES
STORING UP ELECTRICITY.--In the foregoing chapters we have seen that,
originally, electricity was confined in a bottle, called the Leyden jar,
from which it was wholly discharged at a single impulse, as soon as it
was connected up by external means. Later the primary battery and the
dynamo were invented to generate a constant current, and after these
came the second form of storing electricity, called the storage or
secondary battery, and later still recognized as accumulators.
THE ACCUMULATOR.--The term _accumulator_ is, strictly speaking, the more
nearly correct, as electricity is, in reality, "_stored_" in an
accumulator. But when an accumulator is charged by a current of
electricity, a chemical change is gradually produced in the active
element of which the accumulator is made. This change or decomposition
continues so long as the charging current is on. When the accumulator is
disconnected from the charging battery or dynamo, and its terminals are
connected up with a lighting system, or with a motor, for instance, a
reverse process is set up, or the particles re-form themselves into
their original compositions, which causes a current to flow in a
direction opposite to that of the charging current.
It is immaterial to the purposes of this chapter, as to the charging
source, whether it be by batteries or dynamos; the same principles will
apply in either case.
[Illustration: _Fig. 62._ ACCUMULATOR GRIDS]
ACCUMULATOR PLATES.--The elements used for accumulator plates are red
lead for the positive plates, and precipitated lead, or the well-known
litharge, for the negative plates. Experience has shown that the best
way to hold this material is by means of lead grids.
Fig. 62 shows the typical form of one of these grids. It is made of
lead, cast or molded in one piece, usually square, as at A, with a wing
or projection (B), at one margin, extending upwardly and provided with a
hole (C). The grid is about a quarter of an inch thick.
THE GRID.--The open space, called the grid, proper, comprises cross
bars, integral with the plate, made in a variety of shapes. Fig. 62
shows three forms of constructing these bars or ribs, the object being
to provide a form which will hold in the lead paste, which is pressed in
so as to make a solid-looking plate when completed.
THE POSITIVE PLATE.--The positive plate is made in the following manner:
Make a stiff paste of red lead and sulphuric acid; using a solution,
say, of one part of acid to two parts of water. The grid is laid on a
flat surface and the paste forced into the perforations with a stiff
knife or spatula. Turn over the grid so as to get the paste in evenly on
both sides.
The grid is then stood on its edge, from 18 to 20 hours, to dry, and
afterwards immersed in a concentrated solution of chloride of lime, so
as to convert it into lead peroxide. When the action is complete it is
thoroughly rinsed in cold water, and is ready to use.
THE NEGATIVE PLATE.--The negative plate is filled, in like manner, with
precipitated lead. This lead is made by putting a strip of zinc into a
standard solution of acetate of lead, and crystals will then form on the
zinc. These will be very thin, and will adhere together, firmly, forming
a porous mass. This, when saturated and kept under water for a short
time, may be put into the openings of the negative plate.
[Illustration: _Fig. 63._ ASSEMBLAGE OF ACCUMULATOR PLATES]
CONNECTING UP THE PLATES.--The next step is to put these plates in
position to form a battery. In Fig. 63 is shown a collection of plates
connected together.
For simplicity in illustrating, the cell is made up of glass, porcelain,
or hard rubber, with five plates (A), A, A representing the negative and
B, B the positive plates. A base of grooved strips (C, C) is placed in
the batteries of the cell to receive the lower ends of the plates. The
positive plates are held apart by means of a short section of tubing
(D), which is clamped and held within the plates by a bolt (E), this
bolt also being designed to hold the terminal strip (F).
In like manner, the negative plates are held apart by the two tubular
sections (G), each of which is of the same length as the section D of
the positives. The bolt (H) holds the negatives together as well as the
terminal (I). The terminals should be lead strips, and it would be well,
owing to the acid fumes which are formed, to coat all brass work,
screws, etc., with paraffine wax.
The electrolyte or acid used in the cell, for working purposes, is a
pure sulphuric acid, which should be diluted with about four times its
weight in water. Remember, you should always add the strong acid to the
water, and never pour the water into the acid, as the latter method
causes a dangerous ebullition, and does not produce a good mixture.
Put enough of this solution into the cell to cover the tops of the
plates, and the cell is ready.
[Illustration: _Fig. 64._ CONNECTING UP STORAGE BATTERY IN SERIES]
CHARGING THE CELLS.--The charge of the current must never be less than
2.5 volts. Each cell has an output, in voltage, of about 2 volts, hence
if we have, say, 10 cells, we must have at least 25 volts charging
capacity. We may arrange these in one line, or in series, as it is
called, so far as the connections are concerned, and charge them with a
dynamo, or other electrical source, which shows a pressure of 25 volts,
as illustrated in Fig. 64, or, instead of this, we may put them into two
parallel sets of 5 cells each, as shown in Fig. 65, and use 12.5 volts
to charge with. In this case it will take double the time because we are
charging with only one-half the voltage used in the first case.
The positive pole of the dynamo should be connected with the positive
pole of the accumulator cell, and negative with negative. When this has
been done run up the machine until it slightly exceeds the voltage of
the cells. Thus, if we have 50 cells in parallel, like in Fig. 64, at
least 125 volts will be required, and the excess necessary should bring
up the voltage in the dynamo to 135 or 140 volts.
[Illustration: _Fig. 65._ PARALLEL SERIES]
[Illustration: _Fig. 66._ CHARGING CIRCUIT]
THE INITIAL CHARGE.--It is usual initially to charge the battery from
periods ranging from 36 to 40 hours, and to let it stand for 12 or 15
hours, after which to re-charge, until the positive plates have turned
to a chocolate color, and the negative plates to a slate or gray color,
and both plates give off large bubbles of gas.
In charging, the temperature of the electrolyte should not exceed 100°
Fahrenheit.
When using the accumulators they should never be fully discharged.
THE CHARGING CIRCUIT.--The diagram (Fig. 66) shows how a charging
circuit is formed. The lamps are connected up in parallel, as
illustrated. Each 16-candle-power 105-volt lamp will carry 1/2 ampere,
so that, supposing we have a dynamo which gives 110 volts, and we want
to charge a 4-volt accumulator, there will be 5-volt surplus to go to
the accumulator. If, for instance, you want the cell to have a charge of
2 amperes, four of these lamps should be connected up in parallel. If 3
amperes are required, use 6 lamps, and so on.