Solenoid Fundamentals: Economy Circuit

An alternative method of increasing the torque/force output is to use a continuous 100% duty cycle rated solenoid and apply an over voltage input for a short period of time and then reduce the voltage across the solenoid coil to the 100% duty rated voltage for the hold-on period. Influence on over voltage on the solenoid's characteristic.

a  = characteristic with normal voltage
b  = holding force with normal voltage
c  = effect of over voltage
W1 = available work output at normal voltage
W2 = additional work output available by over voltage

The method of achieving an increased torque/force and a continuous 100% rating for hold-on is to use an economy circuit which switches a resistor in series with the solenoid coil when the operating stroke is completed and the plunger has reached its hold-on position. The conditons which apply during operation are as follows:

Plunger in start position and during operation.

P1 = (I1)2Rs Where I1 = V / Rs

Plunger in end position (hold-on)

P2 = (I2) 2Rs Where I2 = V / RS + Re

P1 = Solenoid input power at start.
P2 = Solenoid input power at hold-on.
Rs = Solenoid coil resistance.
Re = Series economy resistance.
V  = Input supply voltage.

The value of Re must be designed to give a solenoid input power equal to the rated 100% ED power value when switched in series.