Electromagnetic Relay

[jkmi]

I have two questions on electromagnetic relay (EMR)

1. Why is the OFF voltage for the relay coil is less than the ON voltage? In some literature i have found that the OFF voltage is of the order of 10% of the rated voltage of the coil compared to the ON voltage which is above 75% of the rated voltage.

2. Why make va for the relay coil is higher than the break va?

 

[jbartos]

Suggestions:
1. Why is the OFF voltage for the relay coil is less than the ON voltage?
///ON voltage is higher to develop enough force margin to keep relay without any chatter. OFF voltage is then the lower limit of the ON voltage. At certain lower voltage the relay armature/plunger will start chatter and tend to drop off.\\ In some literature i have found that the OFF voltage is of the order of 10% of the rated voltage of the coil compared to the ON voltage which is above 75% of the rated voltage.
///There may be large design margins involved produce for some purpose.\\
2. Why make va for the relay coil is higher than the break va?
///The make VAs for the relay have to overcome the force that involves a large air gap between armature/plunger and electromagnet.\\\

 

[OperaHouse]

The magnetic field decreases with the square of the distance. Play with a magnet. You have a lot of holding force when it is just against steel. Now slip four sheets of paper (about 0.015 inch) between it and the metal. The holding force is a lot less. So you need a lot more voltage to create a stronger magnetic field to pull it in.