Sources of Current. One of the chief difficulties of the average young
experimenter is to secure a satisfactory source of current for operating
his apparatus.
There are three means at his disposal and he may draw his electricity
from
1. A power or lighting circuit;
2. A dynamo;
3. Batteries.
[Illustration: FIG. 26.—A Voltaic Cell. A Voltaic Cell consists of a
Strip of Copper and a Strip of Zinc immersed in a dilute solution of
Sulphuric Acid.]
Only those who are so fortunate as to live in a house wired for light
and power service and supplied from the street mains, are likely to be
able to utilize the first named. Those experimenters who live in towns
where there are no commercial power wires or whose homes are not wired
for such service will have to therefore depend upon a dynamo or a
battery.
A dynamo is a very satisfactory source of current, provided some sort of
power, such as a windmill, water motor or small engine is available for
driving it. A hand dynamo is unsatisfactory for some purposes because
the experimenter is usually unable to drive the dynamo and attend to
other work at the same time.
Batteries are the most expensive source of current but for many reasons,
as explained above, are all that is available to the average
experimenter.
There are two classes of batteries, known as
1. Primary batteries;
2. Secondary or storage batteries.
*Primary Batteries* are those which generate their own current by the
action of some chemical such as, for example, an acid upon a metal.
*Secondary Batteries* derive their current from a dynamo or other source
of electricity and store it away in the form of *Chemical energy* until
it is used up. A storage battery might be likened to a pail, which can
be carried to a dynamo and filled full of electricity. Those who possess
a storage battery can recharge it themselves from the 110-volt lighting
or power circuit, from a dynamo or by taking it to an automobile garage
where recharging is done.
Homemade batteries are not as practical as those which can be purchased
ready made, but the knowledge and experience gained in making your own
are so valuable that every experimenter is urged to start in this way.
Various materials such as zinc, copper, carbon, etc., can be used to
make some very interesting and valuable batteries.
One of the most common mistakes made in reference to cells and batters
is in calling a single cell a *battery*. One cell is a cell. More than
one cell connected together is a *battery of cells* or simply a
*battery*.
The Voltaic Cell.
The first practical cell was invented in 1786 by an Italian professor
named Volta and it is, therefore usually called the Voltaic cell.
A Voltaic cell may be easily made by the experimenter, by placing some
water, mixed with sulphuric acid, in a glass tumbler or a jelly jar and
then immersing therein a strip of zinc and a strip of copper, each about
four inches long and one inch wide. The strips must be kept separate
from one another and should be scraped clean and bright before they are
placed in the solution. A copper wire is fastened to the top of each one
of the strips. The acid solution should be composed of one part of acid,
mixed with ten parts of water.
When mixing acid and water, always remember to pour the acid into the
water and never pour water into acid. Otherwise the solution will
suddenly become very hot and is liable to crack the jar. Acid should
always be mixed in a glass or earthenware vessel and never in any sort
of a wooden or metal receptacle, because it will attack and dissolve
metals and wood.
As soon as the acid has been prepared for the Voltaic cell fill a
tumbler about three quarters full and then immerse the zinc and copper
strips therein. As soon as the strips are in the acid, bubbles will
commence to rise from the zinc. These bubbles are a gas called hydrogen
and are evidence of a chemical action which takes place in a battery.
The zinc is being dissolved by the acid and during the process, sets
free hydrogen gas.
It will probably be noticed that very few bubbles arise from the copper
plate and that there seems to be little chemical action there.
It will also be noticed that if the two wires connected to the strips
are brought together the bubbles will arise from the zinc much faster
than before. That is because, when the wires are connected together, a
complete electrical circuit is formed: The zinc is really being oxidized
or slowly burned. If zinc is burned in the open air or in a fire it will
give out its energy in the form of heat but when it is burned in an acid
solution in the presence of another metal it gives out its energy in the
form of electricity.
The zinc strip in a Voltaic battery is known as the *negative* pole or
cathode, and the copper strip, as the positive pole or anode. When the
electrical circuit is completed by touching the two wires connected to
the poles together, the current is supposed to flow from the positive
pole through the wires and back into the solution through the negative
pole.
If the two wires, instead of being connected together, are connected to
an electrical instrument called a voltmeter the needle or pointer on the
meter will swing over and point to about one volt.
*A Voltmeter* is an instrument for measuring electrical pressure or
*potential*. The pressure of an electric current is measured in *volts*
just as the pressure of water may be measured in *pounds*.
If the copper strip is lifted out of the solution and a carbon plate or
rod also having a wire attached is substituted in its place it will be
found that the voltage or potential has increased to one and one-half
volts. Zinc and carbon are said to have a greater potential difference
than zinc and copper and inasmuch as it is usually desirable for a
battery to have the greatest potential difference possible, zinc and
carbon are employed in the batteries of to-day instead of zinc and
copper.
If the wires are then disconnected from the voltmeter and connected to
an electrical instrument called an *ammeter*, the needle or pointer will
probably swing over until it indicates a current of perhaps ten amperes.
An *ammeter* is an instrument for measuring the volume of an electric
current. An *ampere* is a unit of current and is used to designate the
rate of flow just as feet per second are used to denote rate of flow in
the case of water in a pipe.
If the meter is allowed to remain connected to the cell for a short time
it will be noticed that the pointer will commence to slowly drop back
towards zero.
The cell is then becoming *polarized*, which is to say that small
bubbles of hydrogen which are liberated by the chemical action, collect
on the carbon and cause the strength of the battery to fall off. If the
battery is agitated or the carbon is lifted out and scraped it will be
found that the current will immediately rise again to its first
strength.
It would be a nuisance if it were continually necessary to scrape the
carbon or shake the battery so as to avoid *polarization* and so another
means is employed to secure the desired result.
This is accomplished by introducing certain chemicals into the solution
which will give forth *oxygen*. When oxygen and hydrogen meet under
proper conditions they combine and form ordinary *water*.
*Bichromate of potash* or as it is also often called *potassium
bichromate* is the chemical most commonly employed for this purpose.
[Illustration: FIG. 27.—Ordinary Jelly Glasses, Tumblers, Fruit Jars,
etc, make good Jars for small cells by cutting off the tops.]
Homemade Batteries.
*The materials* required for making batteries, suitable as a source of
current for the experimenter, will not be found expensive in most cases.
*Carbon rods* and *plates* may be purchased from an electrical supply
house but they can also be easily and cheaply obtained from old dry
cells. Dry cells may be split open with a cold chisel and a hammer. Care
should be exercised not to break the carbon in removing it.
The round carbon rods used in arc lamps may be used for making batteries
provided that if they are copper plated, the copper is first removed by
immersing the rod in a bath of nitric acid. If this precaution is not
taken there will be a "local action" set up between the copper and the
carbon and the battery will not be as efficient as it will be if the
copper is removed.
Carbon rods and plates are easily drilled with an ordinary hand drill.
Carbon is quite brittle and breaks easily, therefore only very light
pressure should be used.
While zinc rods and plates may also be purchased they are easily made by
the experimenter who possesses a little ingenuity. The melting point of
zinc is quite low. It can be melted in a small iron pot and cast into
the form of rods or plates in plaster-of-Paris moulds. Plates may also
be cut out of heavy sheet zinc.
[Illustration: FIG. 28.—A Simple Home-made Cell.]
Ordinary jelly-glasses, tumblers, fruit jars, etc., make good jars for
small cells. The tops of fruit jars and batteries can be cut off so as
to make the opening larger.
The cutting can be done with an ordinary glass cutter or by filling a
scratch completely around the jar or bottle, at the place it is desired
to cut it off, with a three cornered file. If a hot poker or wire is
then held against the scratch it will commence to crack along the line
and follow the hot poker as it is drawn around.
[Illustration: FIG. 29.—A Home-made Battery having two Carbon Plates
with a Zinc Rod between.]
Figure 28 shows a simple arrangement consisting of a carbon and a zinc
plate mounted upon a wooden strip. The strip is used to support the
plates and rests across the top of the jar so that the plates hang below
in the solution. Most chemicals attack wood and for that reason it is
well to dip the strip in some hot paraffin. The carbon and zinc plates
are fastened on opposite sides of the wooden strip by means of a round
headed screw and a washer. A wire lead should be placed under the washer
on each plate. If the screw and washer are then smeared with some hot
paraffin or vaseline they will be protected from corrosion.
Care should be used so that the two screws employed to fasten the plates
to the strip do not touch each other in the wood. If they should, the
battery will be "short circuited" and the current will flow through the
screws instead of the wires.
Figure 29 shows an arrangement consisting of two carbon plates mounted
upon a wooden strip. The zinc element consists of a rod set in a whole
in the strip between the two carbon plates.
It will be found that two carbon plates will form a better cell than one
with only one plate or rod.
The arrangement illustrated in Figure 30 shows two carbon rods and one
zinc rod clamped between two wooden strips. The zinc rod is placed in
the center and the carbons to either side.
[Illustration: FIG. 30.—The Elements for a Simple Home-made Cell
composed of two Carbon Rods and one Zinc Rod clamped between two Wooden
Strips.]
The wooden strips are cut away a bit at the points where they clamp the
rods so as to form sort of a groove into which the rods fit without
slipping or twisting. The strips are drawn together tightly at the ends
by two wood screws.
When more than one carbon rod or plate is used in a cell, the carbons
should all be connected together so as to form a single unit.
The drawing in Figure 30 shows a wire twisted around the carbons so as
to connect them together but it would be a far better connection if the
wire was clamped between the carbons and the wood so that it is held
firmly.
Four carbon rods may be utilized by following the suggestion shown by
the drawing in Figure 31.
This consists of a square piece of wood about 4 x 4 inches and one-half
of an inch thick.
[Illustration: FIG. 31.—Four Carbon Rods and one Zinc Rod arranged to
form the Elements of a Cell.]
A zinc rod is set in a hole in the center. Four carbon rods are set in a
circle around the zinc and held in place by screws. All the carbon rods
should be connected together. The wooden top not only serves to support
the carbon and zinc rods, but will also act as a cover for the cell and
prevent the solution from evaporating.
Battery Solutions or Electrolytes.
It has already been shown how cells become "polarized" when the solution
consists simply of sulphuric acid and water. An ordinary acid solution
also has the further disadvantage that the zinc element is continually
consumed by the acid when it is in the solution, regardless of whether
current is being drawn from the cell or not. It is of course consumed
more rapidly when the circuit is complete and current is flowing than
when it is not, but the action is still nevertheless sufficiently rapid
to entirely consume the zinc even in the latter case in a very short
time. If an ordinary acid solution is used therefore as the liquid or
*electrolyte*, as it is technically termed, it is always necessary to
lift the elements out of their solutions whenever the cells are not in
use. They should be lifted out and carefully washed so as to remove all
traces of acid.
[Illustration: FIG. 32.—A Battery of Three Cells arranged so that they
can all be lifted out of the solution at once.]
A milder chemical which does not attack the zinc so rapidly as an acid
is often used wherever a battery is to be employed for ringing bells,
operating sounders, telephoning, etc., and only a small amount is
required.
Sal-ammoniac or chloride of ammonium, as it is also called, is a good
chemical for this purpose. It is very cheap and only requires to be
dissolved in water. A good strong solution should be made and an element
consisting of several carbons and one zinc such as those shown in
Figures 29, 30 and 31 used.
Such a cell will give about 1.5 volts and 3 or 4 amperes. If the current
is drawn from the battery continuously or too rapidly, it will also
*polarize* and the current will begin to fall off. The advantage of a
sal-ammoniac cell is that the elements may be left in the solution when
the cell is not in use, without appreciable waste of the zinc.
A very powerful cell of the non-polarizing type capable of delivering a
heavy current and having an E. M. F. of two volts can be made by adding
some potassium bichromate to a sulphuric acid solution.
An electrolyte of this sort may be prepared by dissolving four ounces of
bichromate of potash in sixteen ounces of water. Add to this, four
ounces of sulphuric acid. The acid should be added slowly and the
solution stirred at the same time.
This solution will be found an excellent one to use with cells having
carbon and zinc elements. The current and voltage are much higher than
those of an ordinary acid solution.
This type of cell also has the disadvantage that the zincs waste away
rapidly when in the solution, regardless of whether current is being
drawn or not. This can be partly overcome by *amalgamating* the zincs
with mercury. In order to amalgamate your battery zincs, procure a
little *mercuric nitrate* from a druggist or chemical house. Dissolve
the mercuric nitrate in a small amount of water and then rub the zincs
with a wad of cotton or cloth which has been dipped in the mercuric
nitrate solution.
The arrangement shown in Figure 32 is a very convenient one to follow in
arranging a battery of three or more cells. The elements of three cells
are all mounted upon a strip of paraffined wood and connected in series.
The three battery jars are placed in a row so that each pair of elements
will dip into their proper jar when the strip is laid across the tops.
Such an arrangement is not only more compact than one having the
elements composing each cell mounted upon separate strips, but will be
found very convenient when an electrolyte composed of bichromate of
potash and acid is used, because all the elements may then be raised out
of the solutions at the same time.
It is possible to place the jars in a frame and arrange a windlass
fitted with a crank so that the elements may be easily raised or lowered
from and to the solution. Such an arrangement is called a "plunge
battery."
Connecting Cells.
Cells may be connected either in *series*, in *multiple*, or in
*series-multiple*, depending upon the number of cells to be used and the
amperage and voltage desired.
[Illustration: FIG. 33.—Showing how Cells are arranged when they are
connected in Series. The Voltage of Six Dry Cells connected in series as
above would be approximately 6 x 1.5 or 9 Volts.]
Cells are in series when they are connected with a wire leading from the
negative pole of one of the positive pole of another, so that the
current flows through each one in turn. Figure 33 shows six cells
connected in series. Cells are placed in series when voltage is the most
important factor. The total voltage of the battery is then equal to the
sum of the voltages of the cells. For example, the voltage of the
ordinary dry cell is about 1.5 and therefore if four dry cells are
connected in series the total voltage of the battery will be six. If six
dry cells are connected in series the voltage at the terminals will be
about nine.
When a heavy amperage is desired, cells are connected in multiple.
Figure 34 shows six cells connected in multiple. It will be noticed that
all the negative poles are connected together to form one terminal,
while all the positive poles form another. The amperage of the average
dry cell is about 20. The amperage of a battery of cells connected in
multiple is equal to the sum of the amperages of the separate cells. The
amperage of four cells connected in multiple will be about 80 and about
120 in the case of six cells.
[Illustration: FIG. 34.—Showing Six Dry Cells connected in Multiple. The
Voltage of such an arrangement would only be 1.5, but the Amperage
available would be six times that possible from Cells connected as in
Figure 33.]
The life of the average dry cell is about twenty ampere hours under
normal conditions. If however the cell is discharged at a high rate, say
for instance, five amperes, it will be found that the life is less than
twenty ampere hours. On the other hand, if the discharge rate is very
low, as for example, one-quarter of an ampere, the capacity of the cell
will be greater. In order to get the most economical service from a
battery it is therefore advisable to lighten the load as far as
possible, and cells are consequently often connected in
*series-multiple* with that result in view. In a case, for illustration,
where it might be desirable to secure a current 4 1/2 volts and five
amperes from dry cells, the series-multiple arrangement could be
recommended. Three dry cells connected in series will furnish 4 1/2
volts and five amperes, but by using two sets as in Figure 35, the load
is divided between them and each set will only have to furnish amperes
to the circuit. *Two sets of cells used in series-multiple will
therefore last more than twice as long as either set would alone.*
The series-multiple arrangement is recommended where cells are to be
used for operating toy trains, induction coils, motors, etc., as being
the most economical.
Always be sure to use large wire in connecting cells. Fine wire offers
considerable resistance to the electrical current and the full benefit
of the batteries cannot be secured when it is used.
[Illustration: FIG. 35.—Showing how to connect a Battery of Cells in
Series-Multiple.]
Use care to scrape all connections so that they are clean and bright.
Tighten the binding posts with a pair of pliers so that there is no
chance of their becoming loose.
Another wise precaution is to always arrange batteries so that there is
a small space between two cells and no likelihood of any of the wires or
binding posts coming into contact with one another so as to form a short
circuit.
After the connections have been carefully made a little vaseline smeared
over them will prevent corrosion.
[Illustration: FIG. 36.—Battery Connectors like that shown above can be
obtained for 1 1/2 cents each and will be found to be very handy.]
Storage or Secondary Cells.
Storage or secondary cells (also sometimes called accumulators), differs
from primary cells in that they will not give forth an electric current
until they have been *charged* by passing an electric current through
them.
[Illustration: FIG. 37.—A Simple Experimental Storage Battery consisting
of two Lead Plates immersed in Dilute Sulphuric Acid.]
The Storage Cell is therefore a very convenient means of taking electric
energy at one time or place and storing it up for future use. From this
it must not be implied that electricity is actually stored in such a
battery. The energy of the electric current is really changed into
chemical energy and this energy produces electricity when the cell is
again discharged.
The superiority of the storage cell over any other form of battery is
universally recognized. The dry cell has an E. M. F. of only 1.5 volts
and deteriorates rapidly with age. The E. M. F. of a storage cell is 2
volts, or 33 1/3 per cent higher. Storage cells will operate almost any
electrical device with increased power over any other form of battery. A
wireless set will send farther, lamps will turn steadier and a motor
will give more power.
[Illustration: FIG. 38.—Showing how to charge a Simple Storage Cell
composed of two Lead Plates immersed in Sulphuric Acid by connecting it
to two Bichromate of Potash Cells.]
If properly cared for, a storage cell will last indefinitely. It may be
recharged an unlimited number of times and is exactly as good as new
each time. A dry cell must be thrown away when discharged.
Storage cells are rated by their output in *Ampere Hours.* An *Ampere
Hour* is the amount of current represented by one ampere flowing for one
hour. A 10 ampere hour cell will give 2 amperes for five hours, 1 ampere
for 10 hours, 1/2 ampere for 20 hours, etc. The ampere hour capacity of
a cell divided by the amount of current being used will determine how
long that current can be drawn before recharging is necessary.
Storage cells may be recharged from any source of *direct* current, that
is, from the lighting circuit, in series with a lamp, from a small shunt
wound dynamo, from dry cells or other primary batteries, or from
alternating current by using a *Rectifier*.
An Experimental Storage Cell.
Storage cells consist of lead plates immersed in an electrolyte of
dilute sulphuric acid.
Cut two strips, one inch wide and five inches long, out of sheet lead
about one-eighth of an inch thick.
Attach a wire to each one of the plates and then immerse them in a jar
full of *electrolyte* composed of:
1. Ten parts of water.
2. One part of sulphuric acid.
Connect the wire leading from the plates to a voltmeter and you will
notice that the pointer will not move away from zero.
Disconnect the wires and mark one plate as the *positive*, by means of a
little cross; mark the other plate *negative*, with a straight line.
Connect two good bichromate cells in series and lead the positive
terminal to the lead plate marked with a cross. Connect the negative
pole of the battery to the other lead plate. Bubbles of gas will
immediately begin to arise from the lead plates. Let the batteries
remain connected for about five minutes and then remove them. If you
then connect the two lead plates to the voltmeter again you will find
that the needle now swings nearly to two volts.
You will also find that your storage cell, for the two lead plates are
now a storage cell, will also ring a bell or run a small motor for a few
seconds.
The two lead plates became *charged* when the current from the
bichromate cells was passed through them. This little experiment
illustrates the principle of the storage cell very well.
A storage cell made of lead plates in the manner just described would
not possess sufficient capacity to make it worth while as a practical
cell. It has been found that if instead of a solid flat plate, a
framework or grid is used, consisting of a set of bars crossing one
another at right angles, leaving spaces between, which are filled with a
paste made of lead oxides, there will be a considerable gain in the
capacity of the cell.
A Homemade Storage Cell.
The storage cell illustrated in the accompanying illustrations is very
simple to make and a battery of them capable of delivering six or eight
volts will prove a very convenient source of current for performing all
sorts of electrical experiments.
[Illustration: FIG. 39.—Showing how the Plates for a Storage Cell may be
made from Sheet Lead by boring it full of holes and filling with paste.]
The plates are cut from sheet lead from one-quarter to five-sixteenths
of an inch thick. The height and width will depend upon the size of the
jars used. There are several sizes of rectangular glass storage cell
jars on the market, and if the plates are made about three inches wide
and three and one-half inches high, they will fit the smallest size of
jar. A lug about one inch and one-half long and three-quarters of an
inch wide is left projecting at the top.
Three plates are used in each cell. Each cell will have an E. M. F. of
two volts when fully charged. In order therefore to have a battery
capable of delivering six volts, three cells will be necessary. Nine
plates will be required for three cells.
The body of the plates should then be drilled full of holes about
one-eighth of an inch in diameter as shown by B in Figure 39.
The plates are now ready for pasting. Select three of the plates and
mark them with a small cross. These are to be *positive* plates when
finished. The paste for these plates is made by mixing red lead with
diluted sulphuric acid. The paste should form a good stiff mixture. Lay
the three plates upon a smooth board and press the paste carefully into
the holes with a flat stick. They are then laid aside to dry and harden.
[Illustration: FIG. 40.—A set of three Plates composed of One Positive
and Three Negatives assembled to form a Cell.]
The six remaining plates are to be *negatives* when finished and they
are pasted in identically the same manner as the positives except that
the paste is made of a mixture of yellow lead and dilute sulphuric acid
instead of red lead.
A pasted plate is shown at the right in Figure 39.
Cut six rectangular pieces, three by three and one-half inches, of heavy
blotting paper or thin whitewood. The thin wood used in the construction
of fruit baskets may be used for this purpose. These rectangles are to
be used as "separators" between the plates.
[Illustration: FIG. 41.—Glass and Rubber Storage Cell Jars which are on
the market for the Electrical Experimenter and may be purchased very
reasonably.]
The plates should then be assembled in groups of three, as shown in
Figure 40. The positive plate is placed in the centre with a separator
on either side. Two negative plates are then placed on the outside. The
lugs on the negative plates should come opposite to each other. A square
lead block having a hole bored through the centre may be placed between
the two negative lugs. The lugs are then clamped together with a binding
post and a screw. The plates are held in a compact bundle by two heavy
rubber bands passing around them.
Each group of plates is then placed in its proper jar and the jar filled
full of a mixture composed of:
1. Four parts of water, and
2. One part of sulphuric acid.
The plates are now ready for forming.
The cells are connected in series by leading a wire from the negative of
one to the positive of another and so on.
The terminals of the battery are then connected to a steady source of
direct current of at least ten volts. The positive pole of the battery
should be connected to the positive of the current source and the
negative to the negative.
The source of current may be (1) the 110 volt D. C. supply in series
with a lamp bank as described in Chapter IV; (2) the 110 volt A. C.
supply after it has passed through a rectifier; (3) another battery, or
(4) a shunt wound dynamo.
[Illustration: FIG. 42.—An empty Storage Cell Grid and also a Pasted
Plate both of which are on the market for experimenters who wish to
build their own Cells.]
The current passed through the storage cells during the forming process
should be about one ampere for cells of the size described above. As
soon as the positive plates of the storage cells have changed to a dark
chocolate-brown color and the negatives to a gray-slate, disconnect the
storage battery from the source of current and proceed to use it just as
you would any ordinary battery. Use it until it is exhausted and then
connect to the charging current again, taking care to make certain that
the positive pole of the battery is connected to the positive pole of
the current source.
After the cells have been recharged and discharged in this manner about
ten times they will be completely "formed" and ready for permanent
service.
Complete directions for recharging storage cells and instructions for
their care and maintenance will be found further on.
The only objection to the storage cells just described is that the paste
is liable to fall out of the plates in time. The plates or "grids" as
they are called used in commercial storage cells are cast in elaborate
moulds which make it possible to overcome this difficulty. Such grids
cannot however be made by the experimenter.
Jars, pasted plates and empty grids may be purchased from well known
firms dealing in apparatus for the experimenter, and with their aid it
is possible to construct a very substantial and durable storage cell at
home.
The empty grids or fully formed plates may be purchased in the following
sizes:
─────────────────────────────────────────────────────────────────
Positive or Negative Plate, size 2 7/8 x 2 1/2
─────────────────────────────────────────────────────────────────
" 3 1/8 x 2 7/8
─────────────────────────────────────────────────────────────────
" 3 5/8 x 5 3/4
─────────────────────────────────────────────────────────────────
" 4 3/4 x 2 7/8
─────────────────────────────────────────────────────────────────
" 4 3/4 x 5 3/4
─────────────────────────────────────────────────────────────────
Glass jars will be found satisfactory for stationary batteries. Rubber
jars are however advisable for portable batteries. Jars of the following
sizes may be easily obtained:
──────────────────────────────────────────────────────────────────
Glass Jar, outside 3 3/4 x 4 x 1 1/2 inches
──────────────────────────────────────────────────────────────────
Glass Jar, outside 3 3/4 x 5 x 1 1/2 inches
──────────────────────────────────────────────────────────────────
Hard Rubber Jar, outside. 6 1/2 x 3 1/2 x 1 1/2 inches
──────────────────────────────────────────────────────────────────
Hard Rubber Jar, outside. 6 1/2 x 6 1/2 x 1 1/2 inches
──────────────────────────────────────────────────────────────────
If the empty grids are purchased, they should be pasted in the same
manner as those plates just described. An empty grid of this type is
shown in Figure 42. A pasted plate is shown along side of it.
The two negative plates in cells of this type are fastened together by
"burning" into a lug, The lugs for this purpose may also be purchased
and will be found inexpensive.
The long lugs on the negative plates are cut off so that they will only
just project through the rectangular holes in the "connecting lug" when
the latter is in place, as shown by A in Figure 43.
The plates are "burned" into the connecting lug by using a red hot
soldering iron to melt the lead until they flow together at those
points. This is a job requiring a little skill and the experimenter had
better practice burning some odd bits of lead together first so as to
avoid all possibility of spoiling his plates.
[Illustration: FIG. 43.—Two Negative Plates "burned" together and the
Connecting Lug used.]
The positive plate is placed in position, as shown in Figure 44.
Wooden separators of the same size as the plates are placed between the
plates and the whole strapped together with heavy rubber bands near the
top and bottom.
The cells are then placed in their jars and the latter poured full of
electrolyte, providing that the batteries are to be of the stationary or
open type.
If it is desirable that they be portable and arranged so that the acid
will not easily spill, it will be necessary to seal them at the top.
The sealing is accomplished by cutting a "cover" strip out of thin wood
which will slip down over the lugs into the jar so that it comes about
one-half an inch below the top. A small hole should be bored in the
centre of the cover strip to receive a short piece of hard rubber or
lead tubing, which will act as a vent and permit the gases formed during
charging to escape or the electrolyte to be emptied at will.
[Illustration: FIG. 44.—The Elements of a Storage Cell composed of two
Negative Plates and one Positive Plate in their proper position.]
The cover strip should fit into the jar tightly so that when the sealing
mixture is poured in it will not run down around the plates or into the
jar.
The top of the battery is then poured full of a molten compound of
asphaltum and pitch.
No attempt should be made to seal the batteries when they contain acid.
The inside of the jar should be clean and dry.
After the cells are sealed and filled with electrolyte they are ready
for either forming or charging, depending upon whether the empty grids
were purchased and pasted by the experimenter or the plates were bought
already pasted and formed.
If they require forming, they must be put through the same forming
process which has already been described.
The finished cells when sealed will appear like those shown in Figure
45, according to the sizes of plates and jars used.
[Illustration: FIG. 45.—Three different sizes of Storage Cells which may
be purchased ready made or built by the experimenter out of prepared
materials as explained.]
Recharging and Caring for Storage Cells.
Storage cells are especially affected by the usage given them. If they
are mistreated they will quickly go to pieces, whereas, on the other
hand if well treated they will last indefinitely.
It is important that the electrolyte used in the cells should always be
of the proper strength. The only accurate method of preparing the
electrolyte is with the aid of a *hydrometer*. A hydrometer is an
instrument for determining the specific gravity of solutions.
It is a little device which looks somewhat like a thermometer. It is
placed in the solution and allowed to float. There is a numbered scale
along the upper part of the hydrometer and the *specific gravity* or
strength of the solution is indicated on the scale by the point which is
level with the surface of the solution.
The normal specific gravity for a storage battery solution should be
about 1.250. The strength can be increased by adding more acid and
decreased by adding water.
Ordinary commercial or technical grades of sulphuric acid and ordinary
water are satisfactory for primary batteries, but the acid and water
used in making the electrolyte for storage cells must be *chemically
pure* if you wish to obtain good results and desire your batteries to
hold their charge while standing.
Storage cells can be recharged with DIRECT current only. A dynamo for
recharging storage cells must be SHUNT wound. The voltage of the
charging current must be greater than that of the storage cells. About
three volts of charging current will be required for each cell of the
storage battery. Cells may be connected in multiple when recharging so
as to bring the voltage of the cells below that of the charging current.
It will of course, however, take much longer to recharge cells connected
in multiple than the same cells connected in series, provided that the
amperage of the current is the same.
Storage cells must not be recharged too rapidly. It is better to
recharge them slowly rather than too rapidly. Two amperes is plenty for
small cells of 10-15 ampere hours capacity. Three amperes is sufficient
for cells of 15-25 ampere hours capacity. Five to six amperes is the
right charging rate for a 40 ampere hour battery and 8 amperes in the
case of a 60 ampere hour battery.
[Illustration: FIG. 46.—A Hydrometer for preparing and testing the Acid
Solution for Storage Batteries.]
Storage cells should never be allowed to stand discharged for any length
of time or the plates are liable to become hardened and "sulphated."
They turn white when they are sulphated. It will take a great deal of
charging and recharging to get them back in shape when once they get in
that condition.
Never short circuit a storage cell or discharge it too rapidly.
Whenever any great amount of sediment collects in the bottom of the
jars, pour out the acid solution and wash the cell out thoroughly with
some pure water.
The plates of a storage cell should always be raised up off the bottom
of the jar, so that any sediment which collects will fall below.
[Illustration: FIG. 47.—The proper way of Recharging Storage Cells from
the 110 Volts D. C. Supply in series with a set of Lamps.]
It is a very good plan to keep the terminals of a storage cell or
battery smeared with vaseline so that they will not become corroded.
You can tell when a storage cell or battery is fully recharged by the
color of the plates. The positives will in that case be a dark chocolate
brown and the negatives a light slate gray color.
A cell which is fully recharged will indicate 2 1/2 volts on a voltmeter
connected across its terminals while the charging current is still on.