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A NEW TYPE OF IGNITION TRANSFORMER.

24th November 1925
Page 32
Page 32, 24th November 1925 — A NEW TYPE OF IGNITION TRANSFORMER.
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A Device Claimed to be Free from the Troubles that _Beset the Induction Coil and to have Advantages over the Magneto.

THE use of battery ignitiOn is not so frequent on commercial vehicles as is the case with touring cars, in connection with which the system is steadily growing, on account of the fact that practic. ally every car made to-day is furnished with either electric lighting or electric (starting, or both. Equipments for either of these purposes naturally include a battery, so what is more natural than that the current available there should be drawn upon for the ignition, more particularly seeing that there is greater certainty and greater efficiency at low speeds with battery ignition than with the magneto, which must be revolving fairly fast before it will give a spark of maximum intensity. With the battery system the intensity of the -spark does not vary with the speed, and it is only necessary to Pass the current to the points for a full-power spark to be given.

In battery ignition an essential feature is the induction coil, which changes the low-tension current obtained from the battery into the high-tension current required for ignition purposes. The induction coil, however, has its weak points, and troubles arise in the way of "shorting," " grounding " of current and occasional :` burning out." But now a snbstitute for the coil has been introduced by an American firm of electrical apparatus manufacturers, in the shape of the Thordarson Primax transformer, for which many advantages are claimed.

Readers familiar with the induction coil will know, of course, that it consists in the main of two coils of fine wire wound around a bundle of straight iron wires, with insulation between the

coils. They will also know that the primary or battery winding is on the inside around the rods, and that the secondary is on the outside again, and that magnetism.: in order to travel from end to end of the core, has to pass through the outside air in doing so, and the magnetic resistance of air is 15,000

times greater than that of iron.

In tin Primax transformer these conditions are very materially altered. In the first place, the core is of the closed type a complete magnetic circuit, having low magnetic resistance and leakage, preventing the great power losses o. the open core construction. This core is not made of iron wire in the usual way, but of thin flat blades of steel .007 in. thick, an arrangement which puts more metal into a given space, increases the power transfer from primary to secondary circuit, and has less magnetic lag, faster action and, consequently; a higher secondary voltage. This ewe is covered with mica wrapping to prevent ahy chance of grounding the windings or connections.

The position of the primary and secondary windings is reversed, the secondary or high-tension wiring being wound directly on to the mica wrapping of the steel core, instead of, as with the induction coil, on the outside of the primary winding. This gives more turns for the same length of Wire, reduces the resistance and increases the magnetic effect. Its position is in the strongest part of the magnetic field, which increases the secondary voltage

from a given primary current. This secondary winding is not' grounded on the core, thus removing any chance of the high-voltage current grounding through the core. It is surrounded by sheat mica, which prevents the escape of high-voltage current to either the ground or the primary circuit, and it as insulated under a high vacuum. This process completely insulates every turn and layer, and removes every trace of air and moisture, whilst the distributor connection is soldered into a hollow ter= minaron th3 case, thus making a continuous copper path for high voltage.

The primary winding differs from the winding of an induction coil, not only in the position it occupies in the construction, but in being made not of wire, but of copper ribbon, which increases• the surface for getting rid of the heat. It is of the single-layer type, and in place of only the three or four layers tsed in construction there are no fewer than 140 layers of ribbon winding, which reduces the voltage difference between layers to less than 3 per cent. of that in ordinary coil windings. It thus obviates short-circuits. Moreover, by being wound underneath the secondary winding, radiation of the heat of Ile primary winding into the secondarywinding is prevented.

A condenser, every unit of which has to stand a 500-volt alternating current breakdown test against puncture, is providel and built into the transformer case. All circuits end at terminals outside the • case, which terminals are plainly marked to carry the ends of the primary, secondary and condenser circuits, and the whole construction is cased in sheet bakelite, with solid brass end plates, the general appearance being as illustrated.

It is claimed for this instrument that you cannot put it out of business, that it will not burn out, will not develop a short, or a ground, or any other of the troubles to which coils are subject, :and that it produces a most powerful fifish.

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