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 conditions which apply during operation are as follows.
Plunger in start position and during operation:
- P1 = (l1) 2Rs Where l1 = 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.