Fig. 4. Fig. 5. Fig. 6
with paste. A feature of the ``chloride'' cells is the use
of separators made of thin sheets of specially prepared
wood, These prevent short circuits arising from scales of
active material or from the formation of ``trees'' of lead
which sometimes grow across in certain forms of battery.
Tudor cell.
The Tudor cell has positives formed of lead plates cast in one
piece with a large surface of thin vertical ribs, intersected
at intervals by horizontal ribs to give the plates strength to
withstand buckling in both directions (fig. 2). The thickness
of the plates is about 0.4 inch, and the developed surface is
about eight times that of a smooth plate of the same size.
A thoroughly adherent and homogeneous coating of peroxide of
lead is formed on this large surface by an improved Plante
process. The negative plate (fig. 3) is composed of two grids
riveted together to form a shallow box; the outer surfaces are
smooth sheets pierced with many small holes. The space between
them is intersected by ribs and pasted (before riveting).
E.P.S. cell.
Many of the E.P.S. ceils, made by the Electrical Power
Storage Company, are of the Faure or pasted type, but the
Plante formation is used for the positives of two kinds of
cell. The paste for the positive plates is a mixture of
red lead with sulphuric acid; for the negative plates,
litharge is substituted for red lead. Figs. 4 and
FIG. 7.
5 roughly represent the grids employed for the negative and
positive plates respectively of a type used for lighting. Fig. 6
is the cross section of the casting used for the Plante positive
of the larger cells for rapid discharge. Finer indentations on
the side expose a large surface. Fig. 7 shows a complete cell.
Hart cell.
The Hart cell, as used for lighting, is a combination of the
Plante and Faure (pasted) types. The plates hang by side
lugs on glass slats, and are separated by three rows of glass
tubes 3/8 inch diameter (fig. 8). The tubes rest in grooved
teak wood blocks placed at the bottom of the glass boxes.
The blocks also serve as base for a skeleton framework of the
same material which surrounds and supports the section. Of
course the wood has to be specially treated to withstand the
acid. A special non-corrosive terminal is used. A coned bolt
draws the lug ends of adjacent cells together, fitting in a
corresponding tapered hole in the lugs, and thus increasing
the contact area. The positive and negative tapers being
different, a cell cannot be connected up in the wrong way.
FIG. 8.--Hart Accumulator.
Gould cell.
In America, in addition to some of the cells already
described, there are types which are not found in England.
Two may be described. The Gould cell is of the Plante
type. A special effort is made to reduce local and other
deleterious action by starting with perfectly homogeneous
plates. They are formed from sheet lead blanks by suitable
machines, which gradually raise the surface into a series
of ribs and grooves. The sides and middle of the blank
are left untouched and amply suffice to distribute the
current over the surface of the plate. The grooves are
very fine, and when the active material is formed in them
by electro-chemical action, they hold it very securely.
Hatch cell.
The Hatch cell has its positive enclosed in an envelope.
A very shallow porous tray (made of kaolin and silica) is
filled with red lead paste, an electrode of rolled sheet lead
is placed on its surface, and over this again is placed a
second porous tray filled with paste. The whole then looks
like a thin earthenware box with the lug of the electrode
projecting from one end. The negatives consist of sheet
lead covered by active material. On assembling the plates,
each negative is held between two positive ``boxes,'' the
outsides of which have protecting vertical ribs. These press
against the active material on the negative plates, and help
to keep it in position. At the same time, the clearance
between the ribs allows room for acid to circulate freely
between the negative plate and the outer face of the positive
envelope. Diffusion of the acid through this envelope is
easy, as it is very porous and not more than 1/32 inch thick.
Traction Cells.---Attempts to run tramcars by accumulators
have practically all failed, but traction cells are employed
for electric broughams and light vehicles for use in
towns. There are no large deviations in manufacture except
those imposed by limited space, weight and vibration. The
plates are generally thinner and placed closer together.
The Plante positive is not used so much as in lighting
types. The acid is generally a little stronger in order
to get a higher electromotive force (E.M.F.). To prevent
the active material from being shaken out of the grids,
corrugated and perforated ebonite separators are placed
between the plates. The ``chloride'' traction cell uses
a special variety of wood separator: the ``exide'' type
of plate is used for both positive and negative. Cells
are now made to run 3000 or more miles before becoming
useless. The specific output can be made as high as 10 or
11 watt-hours per pound of cell, but this involves a chance
of shorter life. The average working requirement for heavy
vehicles is about 50 watt-hours per 1000 lb. per mile.
Ignition Cells for motor cars are made on the same lines
as traction cells, though of smaller capacity. As a
rule two cells are put up in ebonite or celluloid boxes
and joined in series so as to give a 4-volt battery, the
pressure for which sparking coils are generally designed.
The capacity ranges from 20 to 100 ampere-hours, and the
current for a single cylinder engine will average one
to one and a half amperes during the running intervals.
General Features.--The tendency in stationary cells is to
allow plenty of space below the plates, so that any active
material which falls from the plates may collect there without
risk of short-circuit, &c. More space is allowed between
the plates, which means that (a) there is more acid within
reach, and (b) a slight buckling is not so dangerous, and
indeed is not so likely to occur. The plates are now generally
made thicker than formerly, so as to secure greater mechanical
rigidity. At the same time, the manufacturers aim at getting
the active materials in as porous a state as possible.
The figures with regard to specific output are difficult to
classify. It would be most interesting to give the data
in the form of watt-hours per pound of active material,
and then to compare them with the theoretical values,
but such figures are impossible in the nature of the case
except in very special instances. For many purposes, long
life and trustworthiness are more important than specific
output. Except in the case of traction cells, therefore,
the makers have not striven to reduce weight to its lowest
values. Table I. shows roughly the weight of given
types of cells for a given output in ampere hours.
TABLE I.
Capacity in ampere-hours if
Type of cell. discharged in Weight of cell.
9 hrs. 6 hrs. 3 hrs. 1 hr.
Ordinary light-
ing . . . . . 200 182 153 101 100 pounds
'' '' 420 380 300 210 200 pounds
'' '' 1200 1080 880 600 670 pounds
Central station
and High Rate 3500 3100 2500 1700 2000 pounds
'' '' 6000 5400 4400 3000 3200 pounds
Traction . . . 220 185 155 125 40 pounds
'' . . . .. 440 .. .. 90 pounds
Influence of Temperature on Capacity.---These figures are
true only at ordinary temperatures. In winter the capacity
is diminished, in summer it is increased. The differences
are due partly to change of liquid resistance but more
especially to the difference in the rate at which acid
can diffuse into or out of the pores: obviously this is
greater at higher temperatures. The increase in capacity
on warming is appreciable, and may amount to as much as
3% per degree centigrade (Gladstone and Hibbert, Journ.
Inst. Elec. Eng. xxi. 441; Helm, Electrician, NOV.
1901, i. 55; Liagre, L'Eclairage electrique, 1901,xxix.
150). Notwithstanding these results, it is not advisable to
warm accumulators appreciably. At higher temperatures, local
action is greatly increased and deterioration becomes more
rapid. It is well, however, to avoid low winter temperatures.
Working of accumulators.--Whatever the type of cell may
be, it is important to attend to the following working
requirements--(1) The cells must be fully equal to the maximum
demand, both in discharge rate and capacity. (2) All the
cells in one series ought to be equal in discharge rate and
capacity. This involves similarity of treatment. (3) The
cells are erected on strong wooden stands. Where floor space
is too expensive, they can be erected in tiers; but, if
possible, this should be avoided. They ought to lie in rows,
so arranged that it is easy to get to one side (at least)
of every cell, for examination and testing, and if need be
to detach and remove it or its plates. Where a second tier
is plaeed over the first, sufficient clearance space must
be allowed for the plates to be lifted out of the lower
boxes. The cells are insulated by supporting them on glass
or mushroom-shaped oil insulators. If the containing vessels
are made of glass, it it desirable to put them in wooden
trays which distribute the weight between the vessel and
insulators. To prevent acid spray from filling the air of
the room, a glass plate is arranged over each cell. The
positive and negative sections are fixed in position with
insulating forks or tubes, and the positive terminal of one
cell is joined to the negative of the next by burning or
bolting. If the latter method is adopted, the surfaces ought
to be very clean and well pressed home. The joint ought to
be covered by vaseline or varnish. When this has been done,
examination ought to be made of each cell to see that the
plates are evenly spaced, that the separators (glass tubes
or ebonite forks between the plates) are in position and
vertical, and that there are no scales or other adventitious
matter connecting the plates. The floor of the cell ought to
be quite clear; if anything lies there it must be removed. (4)
To mix the solution a gentle stream of sulphuric acid must
be poured into the water (not the other way, lest too great
heating cause an accident). It is necessary to stir the whole
as the mixing proceeds and to arrange that the density is
about 1190, or according to the recommendation of the maker.
About five volumes of water ought to be taken to one volume of
acid. After mixing, allow to cool for two or three hours. The
strong acid ought to be free from arsenic, copper and other
similar impurities. The water ought to be as pure as can
be obtained, distilled water being best; rain water is also
good. If potable water be employed, it will generally be
improved by boiling, which removes some of the lime held in
solution. The impurity in ordinary drinking water is very
slight; but as all cells lose by evaporation and require
additions of water from time to time, there is a tendency
for it to increase. The acid must not be put into the cells
till everything is ready for charging. (5) A shunt-wound
or separately-excited dynamo being ready and running so as
