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A New British Magneto.

17th September 1914
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Page 8, 17th September 1914 — A New British Magneto.
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Which of the following most accurately describes the problem?

The British Thomson-Houston Co. Producing Magnetos in Large Quantities.

One of the first anxieties with which manufacturers of motor vehicles of all kinds in this country were faced a. few weeks ago was the possible deadlock in respect of the supply of magnetos. This anxiety was certainly comprehensible in view of the virtual monopoly which the Bosch Co. had secured in respect of the supply of high-class magnetos. Calmer consideration of the problem revealed, however, the fact that the situation was likely to be one of less gravity than was at first expected on account of several circumstances.

Primarily, this country was found to hold considerable stocks of magnetos of the original kinds, and, secondly, the demand for various types of them for pleasure' cars at once fell away very considerably. Lastly, and what is far more important, it as ascertained that several British experts of first-class reputation had the problem of supplying British-made substitutes thoroughly and promptly in hand. In this last respect, we were ourselves reassured when we learnt officially that the British ThomsonHouston Co., the famous electrical firm of Rugby, would shortly be in a position to supply large quantities of its new Magneto. We are now happy to be able to give early particulars of this new component.

The B.T.H. Magneto is manufactured at the Coventry works of the company, and it is not as a matter of fact, the result of any hurried exploitation of the present circumstances, but of over a year's systematic experimenting both in its electrical laboratories, in hard actual practice on the road and in connection with stationary work. After tests which have included the

severest of service conditions, we are now assured that this magneto has definitely proved itself able to stand up as well a.s the Lest of the rnadhines which it is obviously destined .largely to supersede.

In designing and building this magneto, the company has brought its best electrical experience to bear upon the whole subject, and it is interesting to note that no extraordinary experiments have been tried. Existing construction has been accepted as a satisfaetory criterion, and, as a matter of fact, the new B.T.H. magneto is interchangeable with existing types, and will certainly, we feel sure, give equally satisfactory results. .

The B.T.H. Co. is, of courae,'one of the largest manufacturers in this country of electrical apparatus of all kinds, and it is thoroughly familiar with the need which this class of plant claims in respect of high-grade and accurate workmanship--primary necessities in respect of the construction of such a piece of mechanism as the magneto. As the general design, therefore, of the B.T.H. magneto follows the lines (_.f standard magnetOananufacture, as it has for some while now been accepted, its adoption will entail no change whatever in standard practice The B.T.H. has a base and end plates of aluminium, and is totally enclosed and weatherproof. There is a, fine-gauze protection cover over a small opening in the top of the magneto, and this enables air to reach the armature, a necessity which will be admitted by all those with any knowledge of electrical construction of this kind. The magnets are longer than is usually the case, a change which has, it is claimed, resulted in the attainme.nt of a more permanent magnet, and the securing of a hotter spark at low speeds. The B.T.H. Co. has for years manufactured electrical instruments in which the variation of the permanent magnetic field is not allowed to exceed one per cent., whereas a ar iat ion up to 10 per cent. will not seriously affect the operation of a machine of this kind. Therefore, there should be no anxiety whatever regarding the permanence of the magnets used in the B.T.H. machine. These are manufactured from a. special grade of tungsten steel, which possesses great retentivity.

The armature is neat and compact, the condenser being Contained in a brass cap at one end of the core. Its dielectric consists solely of pure mica sheets, and here again the electrical experience of the company in respect of the manufacture of condensers of all kinds has told its tale. The armature shaft is mounted on ball bearings, the greatest care having been exercised to ensure good lubrication, while, at the same time, oil is totally excluded from the vicinity of the windings. In view of the fact that the Rugby house was the first concern in the United Kingdom to insulate the armatures on their large electrical machines by means of vacuum impregnation, as well as of the company's exceptional experience in regard to armature insulation, it is not too much to anticipate that this all-important portion of the new magneto will be above suspicion. In order that high-voltage windings may be thoroughly reliable, they must be impregnated or filled with some supplementary material which will occupy all the interstices so that the coils may in the end become solid, impervious masses. To accomplish this, the coils, after they are wound, are frequently treated with a bituminous or resinous material liquefied . by heat and forced into the windings -under pressure. Such treatment, however, is unsuited to windings that are to be rotated at high speed, as the prolonged effect of warmth and centrifugal force will more often than not cause such filling material gradually to work out again.

A very effective treatment, which avoids this defect, is secured by the employment as filling material of an insulating substance which cannot subsequently soften. After winding, by the B.T.H. system1 the coil is covered with a heavy jacket of suitable insulating material,. which, by subsequent treatment, is converted into a homogeneous waterproof unit. As an additional safeguard for the armature insulation, a safety spark gap is provided, which, in the event of the voltage rising to an abnormal value, acts in

the usual way as a safety valve.to prevent breakdown of the insulation.

The construction of the contactmaker is shown in one ,of our illustrations. This is easily accessible and detachable. Special attention has been given to the contact points ; they are very substantial, and will obviously ensure long life. B.T.H. magnetos are already available in three sizes : the smallest is suitable for single-cylinder motorcycles, whilst the two larger sizes can be used on four-cylinder engines for commercial vehicles. -We learn that other sizes are in course of preparation.

We feel sure that those of our readers who are particularly interested in petrol-vehicle construction will read of this company's preparations to overcome the threatened dislocation owing to the cutting off of supplies of German magnetos with considerable interest.

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Locations: Coventry

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