Using a D2E-S-DC12V to Switch RF at 6M

 

Initial tests are encouraging. Insertion loss less than 0.3dB and both isolation and return loss around 35dB.

Time now to put it on the 6m radio and see how it copes with 50W of FM.

73's

Richard

Relay Life for Relay #2

After some 10 days of continuous operation the test board flash memory was full with over 2 million cycles of data at a constant 2 Amps using a constant current generator. Below is a picture of the actual relay, nearly destroyed when it was removed from its original PCB.

 

I chose this recovered relay because it was damaged. It was surprising that despite the abuse during removal the results, below, show there was no real degradation over 2 million cycles at the rated contact current capacity. Perhaps 30 volts at 2 Amps would give a different result compared with 12 volts at 2 Amps. But for now I am completely satisfied that this relay, of which I have recovered dozens, will be a suitable basis for use as a 50 watt 6m changeover relay.

 

To put this in context the ADC returns a reading of 214 for 0.685volts. For each cycle 16 readings (the graph was wrongly label as the sum of 8 readings) of the voltage across the relay contacts is taken, summed, and stored for the analysis. So a sum of say 200 means there was 40 mV across the terminals. With 2 Amps passing through the contacts that means the resistance was 20 milli-ohm (0.020 ohm).

That is probably enough from me on the subject of relay life. I'm satisfied that operated within the specified ratings a relay, even when recovered, is not going to wear out. All you have to watch out for is  relays re-printed with over-stated specifications sold by the Chinese on Ali-express etc. Similar to the ludicrous ratings printed on 18650 lithium batteries they sell.

73's

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