Relay life - Degradation after 4.7 million cycles

 Just to recap:

• 1.8 million cycles switching a 2 Amp constant current
• Added an RC network giving some 10Amps on contact closure falling to 2Amps constant current
• Ran for a further  1.3 million cycles
• Got impatient, reduced R to give >10 Amps on contact closure falling to 2Amps constant current
• Ran a further 1.6 million cycles (Run 6 and onwards below)
  

 Total cycles now 4.7 million. For the 2.9 million observations with the RC network we see:

 

The analysis of variance by group shows run 11 had an increase in average contact resistance of around 8% and much greater variability. 

 

The 15% increase from run6 to run11 means the relay contacts are dissipating 32% more heat when closed.

I'm going to hit a total of 5 million cycles with the next run. 

73's

Relay Life - Cumulative 3.4 Million Cycles

We have endured some of the worst storms over the last few days. Lightning close enough to trip circuit breakers!

Did that bother the relay?  It's now 1.6 million cycles since I added the RC network and still the relay clicks away.

The variation in the contact resistance measurements looked interesting. And some statistical tests confirmed that the latest run was in fact different. The contact resistance is now starting to increase with the latest run of observations being approximately 10% higher on average. An increase that is statistically significant.

 

So perhaps failure is getting closer? Only one way to find out. Clickety click.

73's

23cm FM receiver - 1st Mixer Stage

Autumn starts in a few days bringing the promise of cooler days. So back to the 23cm project. I decided, based on what was in the junk box, to use a MAX2681 mixer. Reasonably cheap if you have to buy one I was able to salvage a couple from 900MHz data modems. 

One of the unforeseen bonuses with this part is the input matching at 23cm.

The input impedance is 50-j133 ohms. So a 16nH inductor in series with the input pin will cancel the input reactance. 

Too easy!

73's