
74 Electric Motors and Drives
coils with twice as many turns of wire having only half the
cross-sectional area of the original. The full speed would be
the same at
24
V as the original was at
12
V, and the rated
current would be
2
A, rather than 4 A. The input power and
output power would be unchanged, and externally there
would be no change in appearance, except that the terminals
might be a bit smaller.
Traditionally d.c. motors were classified as shunt, series,
or separately excited. In addition it was common to see
motors referred to as 'compound-wound.' These descriptions
date from the period before the advent of power electronics,
an