Improvements in Means for Controlling or Directing Electric Currents.
Year: 1895

page_text: CUMLELE DIBUIFICATION.
Improvements in Means for Controlling or Directing Electric
Currents.
I, CHARLES POLLAK, of No. 253 Mainzer Landstrasse, Frankfort-on-the-
Main, in the German Empire, Managing Director, of "The Pollak Accumulator
Works"
a Joint Stock Company, 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:-
There occur many cases in the practical applications of electricity where it is
necessary that the current passing through a conductor should constantly follow a
predetermined direction as on this condition depends either the attainment of a
desired effect, or the prevention of an undesired effect.
Thus, for example, in an arc lamp, arranged for operation by continuous current
the current should enter in one direction only, the lamp being inoperative during
the passage of a return or reversed current; while in charging accumulators, or
storage batteries, the current should not flow back to the machine lest dangerous
disturbances should occur in the operation.
In such cases, therefore, a continuous current only may be employed, in addition
to which suitable switches or apparatus may be provided, to prevent the current
being reversed.
The employment of alternating currents, as such, has been hitherto quite out
of the question, where circumstance, such as those herein before referred to,
prevail.
The present invention has for its object to provide simple means for preventing
currents from entering an electrical conductor in a direction other than that in
which it is desired to enter, no matter whether such currents be derived from a
source of continuous current or from a source of alternating current.
Taking, for example, the case of a decomposition cell containing an electrode of
lead and one of aluminium, and an alkaline, or acid, solution as an electrolyte : if
the current enter through the lead electrode, that is to say where the lead electrode
is connected to the positive pole and the aluminium electrode to the negative pole
of the source of current there will develope in the cell a counter electro-motive
force of polarization amounting to, say, two volts, resulting in a corresponding
reduction of tension at the poles of the source of current. Apart from this,
however, a current may pass through the cell unimpeded in that direction. If, on
the other hand, the current enter the aluminium electrode first, i.e., where such
electrode is connected to the positive pole of the source of current, while the lead
electrode is joined on to the negative pole, there will immediately form, upon the
aluminium electrode, a polarization coating capable of retarding the passage of the
current owing to its very high resistance or to the counter electromotive force
which will develop in the coating, even where there are very considerable differences
of potential at the two plates of the cell.
Where the plates used are of good quality, the resistance opposing the passage
of the current in this direction i.e. from the aluminium, through the electrolyte, to
the lead, is such that the counter electro-motive force equals the electro motive force
of the source of electricity, so that no current can in this direction pass through the
cell. A noteworthy feature, in this connection, is, that the tension of the source
of electricity, in a single cell of this description, may be an excessively high
one, amounting, indeed, to no less than 120 volts and upwards, and yet may fail
to effect a passage of the current through the cell from the aluminium towards the
lead; so completely is the current from the source of electricity detained.

page_text: .
Where, however, the current is reversed, i.e., where the lead electrode is
connected to the positive pole and the aluminium electrode to the negative pole of
the generator the polarizing coating disappears from the aluminium, or becomes
so modified as no longer to oppose any appreciable resistance to the passage of the
current; whereas at the lead electrode, as already explained, there developes a
counter polarization electro motive force of only about 2 volts.
The same phenomenon may be utilized and made serviceable for manufacturing
purposes in the case of many other metals such for example, as magnesium, zinc
and others, while the electrolyte, in these cases, instead, consists not only of
alkaline solutions, but of other suitable bodies besides, which may be used in a
solid, gaseous, fused, or any other suitable state.
The method of operation of the cells, when employed to act as means for
directing and transforming currents, will be best understood by reference to the
examples illustrated by the accompanying diagrams; the shape dimensions and
distance apart of the electrodes of each cell being of course calculated to suit
given circumstances, and the requisite loss of tension at the cells, which is called
forth by polarization, may be regulated or adjusted at will by connecting such cells
either in series or in parallel.
Figure 1 is a diagram of an arrangement suitable in cases where a storage
battery (such as S), is to be charged from a continuous current dynamo G. Z shews
the electrolytic decomposition cell or series of cells placed in circuit.
electrode is connected to the positive pole of the source of current.
The lead
If the tension of the charging current fall below that of the storage battery, the
current would be reversed and would imperil the machine. Before, however, it can
do this, the aluminium electrode, constituting the polarization electrode, will have
assumed a polarization coating, which will effectually prevent the current from
passing.
As soon, however, as the proper conditions have been restored, and as soon
therefore, as the aluminium again constitutes the cathode and the lead the anode
the polarizing coating will disappear, and the cell will no longer offer any
appreciable resistance to the passage of the current in the normal direction; in
which case the operation of the cell will be similar to that of a "minimum or
current-reversing automatic device.
"
The cell herein described is particularly important and serviceable in cases
where it is necessary that out of a series of current-impulses given in alternate
connections, only those following one predetermined direction are to be utilized
for example where continuous current arc lamps, or continuous current motors,
electrolytic baths or storage batteries are to be fed, from an alternating current-
circuit.
W in Figure 2 represents a source of alternating current; B and M represent
continuous current arc-lamps and motors respectively and Z is a decomposition cell
as herein before described.
Where the connection is made in this manner, one half only of the current-
impulses yielded by the source of current can pass through the cell, namely those
which, in thus passing, are directed from the lead to the aluminium, since impulses
taking place in the opposite direction are checked by the cell.
In order to enable the currents to be utilized more economically, either two
circuits may be provided with two cells, as illustrated in Figure 3, so that such cells
receive or intercept singly the alternately directed impulses; or as shewn in
Figures 4 and 4 four cells may be so connected as to cause all the impulses
to go through the system of working conductors in a uniform or unvarying
direction.
Supposing that at any given moment the source of the alternating current has
the polarity indicated in Figure 44; then the current will take the direction
indicated by the arrow heads which direction is here supposed to be the direction
required. At another predetermined period the polarity of the source of electricity
will be reversed, as indicated in Figure 4B, the current flowing through the circuit

page_text: actually in use will however retain the same direction as before. These cells, will
therefore act in a manner which may be likened to the action of the inlet and outlet
ports of the slide valve of a steam engine.
Under certain circumstances, two electrodes of a different nature, without any
electrolyte, may be employed instead of the cells above described by way of
example, and in those cases, a polarizing coating will form on one of the electrodes
owing to the co-operation of a layer of moist air between the contact surfaces, or
owing to the direct action of gases upon those surfaces; which coating will disappear
as soon as the direction of the current is reversed.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
A device for controlling or directing electric currents, consisting of an electrolytic
cell which is introduced into the circuit and which contains an alkaliue or other
electrolyte and two electrodes of a different nature, one of which, during the
passage of the current in such a direction, that that electrode becomes the positive
electrode, assumes a polarizing covering or coating which by its resistance or its.
counter-electromotive force effectually checks the passage of the current in that
direction, while in the opposite direction it allows the current to pass without any
appreciable diminution of tension.
Dated this 10th day of September 1896.
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.