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:
- 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.
- Opening and closing times have no strong correlation with contact resistance so I will not be recording them any more.
- 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
