Spark coil

“ It requires a vastly higher voltage to make a spark jump across an air gap than it does to lead it across thus.
Fig. 116
The kind of coil we have made (only larger) is very much used in houses as a gas-lighting coil (to be described later) . It is very much used also for exploding gasolene engines. It generally passes under the name of the "make and break" coil. The revolving shaft of the engine is made to push together the ends of the wire and separate them at the right instant to make the spark for explosion. Of course this is done inside of the engine cylinder. ”

“ Spark-Coils A "spark-coil" is one of the most interesting pieces of apparatus an experimenter can possess. The experiments that may be performed with its aid are varied and many.
The purpose of a "spark-coil" is to generate enormously high voltages which are able to send sparks across an air space that ordinary currents of low voltage could not possibly pierce. The spark-coil is the same in principle as the small induction coils used as medical or shocking coils, but is made on a larger scale and is provided with a condenser connected across the terminals of the interrupter. ”

“ As in the simple electromagnet, the proportions of diameter and length of the primary coil and core will determine its rapidity of action. A short fat coil and core will act much quicker than a long thin one. But on a short fat coil the outside turns would be too far removed from the intensest part of the primary field. A good proportion of core length is given in the following table:
The primary coil P consists of two or not more than three layers of insulated copper wire of large diameter, being required to carry a heavy current in a 2-inch spark coil, probably from 8 to 10 amperes. ”

“ If the spark coil is a good one and capable of giving a good hot spark, it may be possible to tell when the set is in proper tune by placing a small miniature tungsten lamp in series with the aerial and changing the clips, the condenser, and the length of the spark-gap until the lamp lights the brightest. ”

“ The 150-volt alternating current from the bell is more tolerable than that from a 150-volt dynamo, because the quantity is limited in the former case.
Our spark coil has a vibrator which acts precisely like the hammer of the bell to make and break the primary circuit and thus make rapid changes in the magnetic field produced by the primary coil. The primary coil of the spark coil is many times larger than the coil of the bell, that is, it contains many more turns of wire. It has much more iron in the core. ”

“ What Ratio of Transformation Means.--To make a spark coil step up the low voltage direct current into high potential alternating current the primary coil is wound with a couple of layers of thick insulated copper wire and the secondary is wound with a thousand, more or less, number of turns with very fine insulated copper wire. If the primary and secondary coils were wound with the same number of turns of wire then the pressure, or voltage, of the secondary coil at its terminals would be the same as that of the current which flowed through the primary coil. ”

“ A one-inch spark coil will give very good results by connecting the spark-gap directly across the secondary of the coils. The aerial is connected to one side of the gap and the ground to the other.
The transmitter may be "tuned" and the range sometimes increased by using a condenser and a helix.
A condenser is most easily made by coating the inside and outside of a test-tube with tinfoil so as to form a miniature Leyden jar. The end of the tube is closed with a cork through which passes a brass rod connecting to the inner coating of tinfoil. ”

“ The secondary windings of coils are often punctured or broken down by operating the coil with the high tension circuit open, or by trying to cause long sparks by increasing the spark gap over 3⁄8 of an inch in the open air. Coils are also broken down by allowing excessive currents to flow in the primary coil. Never cause a spark to jump over 3⁄8 of an inch.
High compression in the cylinder shortens the jumping distance of a high tension spark. ”

“ By means of the condenser connected across the interrupter terminals, the current at "make" is caused to take a considerable fraction of time to grow, while at "break," the cessation is instantaneous. The currents induced in the secondary at break are so powerful that they leap across the space in a brilliant torrent of sparks.
Building a Spark-Coil Perhaps more attempts are made by experimenters to construct a spark-coil than any other piece of apparatus, and the results are usually poor. A spark-coil is not hard to construct, but it requires careful work and patience. ”

“ The trembler blade is shown at D, with the adjusting screw F 58and the platinum-tipped contacts G1, G2. The iron core of the coil projects a little above the case, as shown at E in Fig. 50. The strength and character of the spark may be varied considerably by slightly screwing F up or down. When current is supplied to the low tension terminals of the coil it flows through the primary winding and magnetizes the iron core, completing its circuit by passing across the platinum contacts. ”

“ All that is necessary to get a spark is to provide a suitable resistance coil with an iron core, so that the fuse will not be blown and to secure sufficient inductance to get a hot spark. The writer uses an ordinary 50-ohm telephone induction coil, in which the primary and secondary are placed in series by the diagonal connection indicated in the sketch. ”

“ Four to eight large cells of dry battery are used, or eight cells Edison-Lalande—iron-clad type. Number of cells varies with size of coil needed, some classes of engines require a heavier spark than others to ignite the vapor.
When a primary and secondary are used, the primary should be made of two or three layers No. 14 B & S magnet wire, and a secondary of one pound No. 34 B & S magnet wire. There can be an independent contact breaker or the coil can be made up similar to a one-half inch spark Ruhmkorff coil (see Chapter I.) .
Fig. 12. ”

“ The intensely disruptive power of the long spark is readily shown by its power to perforate substances, but great care must be taken that the secondary wires of a coil are led away from the body of the coil. A good plan is to hang two silk cords or stout threads from the ceiling, to which the secondary wires may be attached and kept in sight when experimenting at any distance from the coil. ”

“ The induction-coil is fitted with a trembler or interrupter, which easily gets out of order and which must be regulated with considerable accuracy. The spark-plug is a particularly delicate part, subject to many possible accidents. The porcelain of which it is made is liable to crack. ”

“ If a heavy discharge of sparks takes place between the end of the cable and the metal of the engine, the coil is in good condition.
If a partial short circuit exists, the spark at the gap will be weak and without heat; the result will be intermittent, or misfiring with a loss of power. Moisture in the cylinder is a common cause of plug short circuits, the moisture coming from leaks in the water jacket or from the condensation of gases in a cold cylinder. A drop of water may bridge the spark gap, allowing the current to flow from one electrode to the other without causing a spark. ”

“ If, however, much higher speeds are employed, then the time of contact becomes abbreviated, and the ability of the coil to charge a capacity is diminished.
Professor J. Trowbridge has described an effective form of motor break for large coils, in which the interruption is caused by withdrawing a stout platinum wire from a dilute solution of sulphuric acid, and by this means he increased the spark given by a coil provided with hammer break and condenser from fifteen inches to thirty inches, when using the liquid break and no condenser. ”

“ When the Ruhmkorff induction coil is joined to the electric circuit a series of violent discharges of great rapidity occur between the tube terminals, resembling in their power the discharge of a Leyden jar, though for want of a dense atmosphere the brilliant spark has been replaced by a glow and brush-light in the tube. The coil is of large dimensions, capable of passing a spark across an air-gap of ten to twelve inches. It will perhaps increase the reader’s respect for X-rays to learn that a coil of proper size contains upwards of thirteen miles of wire ”

“ With this coil, when fairly well produced, they are about 25 to 30 centimetres long. When the hand is held against them no sensation is produced, and a spark, causing a shock, jumps from [Pg 220] the terminal only upon the hand being brought much nearer. If the oscillation of the primary current is rendered intermittent by some means or other, there is a corresponding throbbing of the streams, and now the hand or other conducting object may be brought in still greater proximity to the terminal without a spark being caused to jump. ”

“ The coil and batteries or magneto by no means form the entire ignition system, although the generation of the spark depends entirely upon them. The spark must be regulated to occur at the proper point in the stroke of the piston, as a continuous spark would not only waste the current, but would cause the ignition of the charge during the upward stroke and would result in an impulse in the reverse direction that would prevent the motor from running for more than half a turn. ”

“ By this simple arrangement of two coils we can thus exalt a current of low pressure to one of high electro-motive force. A battery current which can barely produce an electric spark of one hundredth of an inch at the ends of the coarse coil can cause a spark of eight inches or more at the terminals of a fine coil. ”

“ Remember that a hot spark causes rapid combustion, and will fire a greater range of mixtures and “leaner” charges, than a straggling, thin, weak spark. Spark coils that give poor results with a long spark gap under high compression are often benefited by the shortening of the spark gap. Shortening the gap will increase the heat of the spark, and will insure the passing of a spark each time that the timer makes contact. ”

“ The commutator should be kept clean and well oiled at all times.
One is located at the top of each cylinder and can easily be taken out with the spark plug wrench included with every car, after the wire connection is removed. The high voltage current flows out of the secondary coils in the coil box and on reaching the contact points in each spark plug it is forced to jump a 1/32" gap, thereby forming a spark which ignites the gasoline charge in the cylinders. ”

“ The vibrator on the coil causes the magnetic field to rapidly vary in strength. This induces a secondary current in the whole coil which, because it passes through a very great number of turns, has a high voltage. This passes from C through B to the base of the engine, then up the walls of the cylinder to the plug f, then jumps across the gap at a, causing the spark which explodes the mixture of gasolene and air in the cylinder. The spark plug f is porcelain—an exceedingly good insulator. Through the centre of this passes a wire from a to e. ”

“ Starting is accomplished by spraying cold gasoline into the cylinder through the fuel valve in the same manner that the heavier oil is fed during operation, and the ignition is performed by a high tension coil and batteries. No spark time device is used, so that a continuous shower of sparks is thrown into 189the mixture during the starting period. Within a minute after the engine is started, the ignition switch may be opened, the gasoline cut off, and the heavy oil turned on for continuous running on full load. ”

“ By modifying the ordinary induction coil, so as to make it yield a highly heating spark, and remedying its property of losing tension rapidly after leaping four or five solutions of continuity, the Messrs. ”

“ A coil much used for electric baths has a primary winding only, regulated by the sliding in and out of the iron core, which necessitates the use of an independent vibrator, or else by varying the current strength with a rheostat. The general directions given before will answer in the present case, the only data necessary being the size of wire, which should be about six to ten layers of No. 20 B & S. The coil with movable secondaries here comes into service. Strong currents are needed for bath work, and any variety of winding can be used with this make of coil. ”

“ It is absolutely essential that the diameter of contacts for all contact breakers should be as large as possible and their faces filed truly parallel to enable them to easily carry all the current required. One of the main causes of failure of coil is burning of the platinum point and platinum burr, the current being then materially reduced. Large sparks at point of rupture are often indications that the condenser is not working properly—perhaps has broken down or is not large enough. ”

“ The decomposition of water, which consists of oxygen and hydrogen in the formula H2O, is readily accomplished by the secondary current, and the greatest volume of gas (hydrogen) will be evolved at the negative pole. For ready reference a summary of these facts is given 45below:
Although it is customary to use bundles of fine, soft iron wire for coil cores, very excellent results have been obtained with cores made up of soft iron filings. ”

“ There is nothing quite so startling as to receive an electric shock unexpectedly and such a shock may be given to a friend while shaking hands upon meeting. The shock produced is not harmful and the apparatus can be carried in the pocket. It consists of a small induction coil that can be constructed at home.
The core of the coil, A, Fig. 1, is constructed in the usual manner, of small soft-iron wire to make a bundle about 3/16 in. in diameter and 2 in. long. The coil ends are made from cardboard, about 1 in. in diameter, with a 3/16-in. hole in the center. ”