|Maximum applied voltage
The permissible maximum applied voltage of a given relay coil changes with ambient temperature. The coil temperature rise (the self-heat temperature, i.e., the applied-voltage-dependent portion) is the difference between the permissible temperature specified by relay design and the operating temperature.
Refer to the coil voltage vs. temperature derating characteristics in the Technical Documents for this value. An example is shown in Fig. 5.
The permissible temperature of relay operation is determined mainly by the coil wire and plastic materials used. In the case of the NEC Miniature Signal Relays, the standard specification is set at 120°C.
As the applied coil voltage increases, the operate time becomes shorter. However, the bounce in the make contacts becomes longer, increasing the contact opening or closing frequency. This may affect the life of the contacts.