Pulse Operation of DC Solenoids


Posted on Feb 7, 2014

With pulse operation, the solenoid is energized momentarily with five to six times its rated voltage, then held in with less than half of its rated voltage. Application time is reduced drastically and the reduced holding voltage produces less arcing when the circuit is opened. Additionally, a well regulated d-c power supply is not required. With switch S open, capacitor C charges to the line voltage value, VL. If a 24vdc


Pulse Operation of DC Solenoids
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solenoid is used with a 120vdc line, the solenoid receives five times its rated voltage when the switch is closed. After switch closure, solenoid voltage, Vs drops sharply due to resister R. Since power varies with the square of voltage, reducing the holding power to 1/2, reduces power dissipation to 1/4. Because poor regulation is permissible, a simple half wave rectifier converts the a-c source to a d-c voltage. Capacitor C charges to the peak line voltage at approximately 160 volts, for a standard 115 volt line. Operation from a dc source is the simplest CASE, Fig. 1. After selection of a solenoid rated at approximately 20% of available peak line voltage, values of R and C must be determined. Resistance determines the holding current. Most solenoids in the 9 to 12 watt range will remain energized at 10% to 20% of rated voltage. Limiting voltage to 1/2 to 1/3 rated voltage assures sufficient holding force. Resistance R is calculated from: Where VL is line voltage, Vs is required solenoid holding voltage, and Rs is solenoid coil resistance. To hold a 24vdc solenoid at 1/3 rated voltage ( 8vdc): Capacitance requirements for the pulse operation circuit are not so easily determined. The capacitor must store sufficient energy to establish the required magnetic field in the solenoid; this field must persist long enough to accelerate the moving parts actuated by the solenoid. The solenoid will not remain energized if the...




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