Three Methods for Reducing Nominal Operating Power in Relays

November 14, 2016
By Bethany Dunich

Every day energy is being wasted through inefficient technologies – ultimately costing people money. To help alleviate this issue, new features are being added to the components designed into various devices. Relays, for examples, can have huge energy saving benefits when designed into applications like Photovoltaic (PV) Systems.

The nominal coil holding voltage of a Relay can be reduced 100 milliseconds after the contacts have closed.  Relays can minimize the impact of the entire systems power consumption by taking advantage of reduced coil holding voltage techniques.  Here are the three most common methods to reduce coil holding voltages.


Apply a voltage over nominal coil voltage (around 130%V).  After the Relay is ON, the power consumption is controlled using the values of the Relay coil resistance, Capacitor and Resister (R).



Operate by turning on SW1 at the nominal voltage.  After the Relay is closed, turn SW2 on and release SW1.  Set the coil holding voltage using resistance (R), and the Relay coil resistance to reach the voltage you are aiming for (around 50%V).



Turn the MOSFET on to supply voltage to the Relay coil and make sure the duty ratio is at 100%.  After the contacts are closed, start PWM control with MOSFET duty ratio at 50% and control the power consumption.  A recommended PWM control frequency is 20kHz to 100kHz.


To achieve the lowest coil holding voltage using the above methods, it is important to design in the appropriate Relay. Below is a list of recommended Relays, manufactured by Panasonic, and their specifications. These Relays are some of the best in the industry and can achieve the lowest operating coil holding voltage.

Product Contact Arrangement Current Capacity Coil Holding Voltage Nominal Operating Power Coil Holding Power Consumption
LF-G 1FormA 22A, 31A 35%V of nominal coil voltage 1,400mW 170mW
HE-S 2FormA, 2FormA + 1B 35A 30%V of nominal coil voltage 1,880mW 310mW
HE-PV 1FormA 35A, 48A, 90A 40%V of nominal coil voltage 1,920mW 170mW

To learn more about Panasonic Relays, click here or contact your local Panasonic sales representative.