Well I'm feeling disappointed. I had thought that by now some evidence of degradation would be visible in the contact resistance. But after operating the relay 262,000 times I don't see any strong evidence the end of life is near. The ADC reading for the voltage across the closed contact has been quite consistent over time. The variability could be due to fluctuations in ambient temperature and RF interference from cellular and wifi sources.
I'm going to modify the code so that 8 readings of the contact resistance are taken, instead of the present 16. That will allow me to record twice as many cycles before filling up the 32mb memory chip. It will also reduce the "on" time each second which will reduce the temperature of the LM317 used in the 2 Amp constant current generator. I suspect the LM317 gets hot enough that the temperature protection is causing the current generator to fold back to a lower figure.
But I am starting to wonder if switching 20% of the rated current means the life is governed by mechanical, not electrical, failure. That would be over a million cycles.
73's
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