Page:Motors and motor-driving (1902).djvu/335

Rh to treat of them here. As regards the gearing breaking or stripping, that is comparatively inexcusable in an electromobile, as the kind of effort which an electric motor exercises is a steady and continuous one, and the gearing is subjected to none of the jerks and jars which occur when an explosion engine is the motive power, and when change-speed gear is varied by an inexperienced hand.

The motors may fail from various causes. The most common of these is burning up, due in general to forcing too much current through them either to get up a steep and muddy hill, or less generally in an attempt to run the vehicle up to or beyond the due limit of speed. When the motor proposes to bum up there is no doubt at all about the fact. It begins usually some minutes previously to diffuse an agreeable perfume, not very dissimilar to the smell of incense, the result of the vaporisation of the shellac which is used in the insulation of the windings. It is quite possible for a motor to diffuse this perfume without actually burning up, this merely being an evidence that the motor is getting extremely hot; but the wise man when he perceives it will usually, if possible, put his controller into position to give less current to his motors. Burning up may take place either in the field magnets or the armature, not very often in both at once. It nearly always means rewinding the part affected an expensive performance. The burning up of an armature, however, is always much worse than the burning up of a field, as nearly everybody can wind a field, but an armature winder is a skilled mechanic, who commands high wages and often puts on airs. Sometimes, without actually burning up, the heating will cause failure of insulation between the windings of a motor, and then the motor, though continuing to run, will take considerably more current for the same power developed. It is better to rewind or get rid of a motor in this condition.

A motor may under circumstances refuse its work altogether, that is to say object to starting, though in a well-constructed car this is a very unusual occurrence. It may be due practically