A Magneto that Gives Easy Starting.
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ANEW magneto was shown to us last week. It has been developed by the experts of the French company, Societe. Magnetos R.B., which has had many years of experience in magneto design, manufacture and maintenance. After a test period of about two years, 50 of the type were put into use on the Citroen cabs in Paris, with ex
cellent results. It has now been adopted by half a dozen of the leading French automobile makers, and the output is now 750 per week. An English company has been formed to exploit it under the title of A. Rist (1927), Ltd., of Waveney Works, Lowestoft, the head of which, Mr. Rist, has himself had a very extensive experience in ignition matters, having been responsible for a very large output of coils and coil ignition apparatus, and therefore having a predilection for coil ignition with its efficiency at low shaft speeds.
The accompanying graph shows the relative good and bad features of /magneto ignition and coil ignition. The magneto has a low spark
energy at slow speeds, the energy improving, as is shown by the line M, as the engine speed rises. In other words it is a bad starter. Coil ignition, on the other hand, gives its greatest efficiency at starting, as is shown by the line B, but its spark energy falls off as the engine speed rises for reasons which are well known and need not here be entered into. A combination of the two is ideal, as is shown in the line C in the graph.
The new Voltex magneto gives a very much better line than the line M, as when the shaft is rotated by thumb and finger it will give a spark in atmosphere about threequarters of an inch in length and at less than 50 revs, per mm., the spark in a cylinder under compression is ample for starting purposes. It is claimed that this result is due to the cleverness of the design.
The magnets are disposed horizontally instead of vertically, the rotor rotates between the laminated pole pieces at .right angles to the position which has hitherto been adopted in magneto design, and a one-piece body is rendered possible. The rotor is carried in two bearings of substantial size, between them being the helical drive for the distributor shaft. The winding is enclosed in a Bakelite case which prevents losses and is stationary. this, again, avoiding breakdowns and losses. The distributor casing is set slightly inclined from the vertical so that it is immediately accessible and it includes the condenser. The two details of any that are prone to breakdown are the winding and the condenser, and it is generally a big job to replace either, so that the usual standby is a complete magneto. In the case of the Voltex a new coil can be inserted in
15 minutes (but, owing to the large size and the heavy gauge wire used, it is less likely to breakdown) and to put in a new condenser is the work of but two or three minutes. Hence if spares be thought desirable those two components are all that need be carried.
Other merits of the Voltex magneto are that its price is low (IS for a four-cylinder machine) whilst for an extra £1 a coil and switch are supplied that provide for both battery and magneto ignition, the alternative primary current being taken from the lighting battery. Dual ignition is undoubtedly the correct thing for commercial vehicles, the engines of. which so often have to be started on cold mornings after the vehicle has been out in the open all night, when covered garage space is not available. With commercial vehicles a quick start has to be made to ensure punctual service.