Overload of Dynamo

—It may happen through some cause or other that a greater output is taken from the machine than it can safely carry. When this is the case, the fact is indicated by exce ive sparking at the brushes, great heating of the armature and other parts of the dynamo, and po ibly by the slipping of the belt Gf a belt-driven machine), resulting in a noise. The causes most likely to produce overload are: (a) exce ive voltage; (b) exce ive current; (c) reversal of polarity of dynamo; (d) ‘Short circuits or grounds in dynamo, or external circuits. If at any time it be nece ary to run an engine driving a shunt or compound dynamo at a lower speed than the normal, the voltage and output of ibe dynamo can generally be maintained at their ordinary value by coupling up the shunt coils in parallel, thus increasing the strength of the current flowing in the shunt circuit and the strength of the field correspondingly. Care should be taken, however, that the coils do not overheat with the increased current.