Relay Life - Tests going forward from 5 Million Cycles

After a cumulative 5 million cycles in total the increase in contact resistance is conclusive. Shown below is the final 3.1 million cycles.

 OK, so I was surprised to lean just how robust these inexpensive Chinese relays are. But I also learned what failure looks like and by using various statistical measures I have concluded that going forward I will:

1. measure the voltage across the contacts and save only the sum of 4 readings. This gives me just as good a measure of increasing resistance as 8 readings.
   
2. Opening and closing times have no strong correlation with contact resistance so I will not be recording them any more.
3. Measurement will start at the same time reading 6 is currently taken. The average of readings 1-5 are statistically different to the last three readings, but that difference is decreasing i.e. reading 1 is more different than reading 5 when both are compared to reading 8. Without the RC network this effect is still present. So perhaps this is a heating effect of passing current through the contacts?

Which all means the external flash memory chip I used can now records over 2 million cycles. Which is fortunate because my interest is switching to these 2Amp signal relays for use as a 50 watt 6m changeover relay.

 

I will test one of these shortly at a constant 2 Amps using a constant current generator. These should fail relatively quickly at 2Amps. I might then redo the test with the RC network with an expectation they will fail really quickly. But all I need is 10,000 cycles to meet my goals. 

73's

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