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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum (src_forum@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by:Lawrence Lacuesta (Lawrence.Lacuesta@tas.alcatel.ca )
Date posted: Tue Apr 3 17:00:43 US/Eastern 2001
Subject: Relay Failures
Message:
hi! The failed relay is solder-mount on a standard 3U PCB, pluggable, ground mobile environment, operating at least 150,000 cycles/year, current rating is 10% of rated load at 1A (lamp). Relay is rated 100,000 cycles @ rated load. Failure Analysis result: The relay contact shorted to the coils was caused by broken moving contact spring. The normally closed contacts remain open when the voltage was removed from the coils (de-energized) was caused by damage/fractured of the over-travel spring and broken weld joint of the armature hinge pivot, which prevented the armature from assuming the drop out position. Per manufacturer, the weakest point on the relay is the spring that is sitting directly on top of the contact pins inside the relay enclosure. Is the above result caused by shock and vibration and not over cycling? Thanks in advance!


Reply:

Subject: Reliability Analysis Center
Reply Posted by: Patrick Hetherington
Date Posted: Wed Apr 4 9:19:49 US/Eastern 2001
Message:
Without doing a thorough failure analysis on the spring and weld, I don't believe it is possible to provide anything conclusive. What is certain is that the spring failed and the manufacturer says it is the weak link. The question is did it fail prematurely. Springs will fail due to fatigue that can be accelerated under higher temperature. Although you are operating at 10% of the rated current, this does not imply the spring should last 10 times as long. Lower current will result in less residual heat and should have a possible impact on spring life. You did not mention how many cycles were on the relay at failure. Vibration will induce additional cycling on the spring.


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