The coil operating current should be pure direct current for optimum
operation. Rectified alternating current may be used but the operating
characteristics, primarily pickup and dropout voltages, may be altered due
to the ripple factor of the rectified current. A capacitor may be used to
reduce the ripple factor to below 5% by applying the following formula:
To calculate the ripple
factor
Ripple factor (%) =
E max. - E min.
E mean
X 100%
E min. = min. value of pulsating
component
E max. = max. value of pulsating component
E mean =
average value DC component
Full wave rectified current may be used but a slight
decrease of attractive force may result accompanied by a change in
vibration and shock resistance.