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Relays Home > Kilovac Home > Non-Power Switching Applications > Momentary or Pulsed Loads Through Closed Contacts
Momentary or Pulsed Loads Through Closed ContactsKilovac vacuum and gas-filled relays can handle momentary current pulses much higher than their continuous current rating. The key is to keep the temperature rise of the relay within safe limits since the normal failure mode in high peak current applications will be either contact welding from very high, very short current pulses or loss of seal integrity of the glass-to-metal or ceramic-to-metal seals due to excessive heat.
** Pulse, 5ms Duration, Closed Contacts; Failure=Welded Contacts *** Pulse, 1s Duration, Closed Contacts Therefore, there are two key parameters you must consider in selecting a relay for this type of application. First, refer to Figure 19 for recommended relays and their estimated peak current pulse rating. Second, you must calculate the duty cycle of the pulse to ensure that you will not exceed, on average, the relay’s continuous current rating. To calculate duty cycle, Pulse duration (in seconds) X pulse rep rate (in cycles per second) x 100 = duty cycle (in percent) The duty cycle times pulse peak current should not exceed the continuous current rating of the relay. For example: A pulse of 50 amps, lasting 50 milliseconds is passed through the relay every 200 milliseconds. The duty cycle is... .050 pulse duration X 1 cycle/.200 seconds = 25% duty cycle The average current is... 25% X 50 amp peak current = 12.5 amps continuous Thus, a relay with a 12.5 amp or greater continuous current rating will be suitable for this application. |