# Electromechanical relay AC load synchronization

I am trying to check the durability of a relay (G5LE family, 5v relay). I wanted if the relay contacts will still work after a certain number of cycles (ex. after 1 million switching cycles).

I am having a problem about switching AC loads. I've done a test where I connected an 83 ohm resistor (multiple wirewound resistors in parallel for more power dissipation capability) with a 230Vrms (main outlet) as the load source.

My input to the coil side is a square wave of 60 Hz, 5 to 0v. After just ~1.5k switching cycles, the relay contacts have failed. The normally open (NO) and common (COM) have become shorted regardless of the input to the coil.

After searching for a bit, I come across this: " It appears that since my switching frequency is also 60 Hz, it may be possible (depending on my timing of pressing the start button of the 60Hz signal generator) that the contact current is at the maximum absolute values (most positive or most negative current) whenever my contact closes or opens. As we know, higher current during contact closing/opening leads to contact material migration (welding of contacts).

I am also thinking that if my coil square wave input happens to start in phase with the 60 Hz load source, then my contact current waveform consists only of positive half-cycles (which results to relatively high average current). Does this negatively affect contact life (compared to say if I have complete positive and negative cycles of current which results to ~0 Amp average).

Now my question is, instead of making a microcontroller code to have "random switching" of the coil, is it possible do the following things instead: -Decrease the frequency of switching so that for every "contact ON time", there a lot of complete cycles (both positive and negative current) so that the average current during this "contact ON time" is roughly 0A?

• Are you saying that you're switching the relay on/off at 60 Hz? And that you expect that 1/60th of a second, no that's on/off so 1/120th of a second, 8.3 ms, is enough time for the relay to close/open properly? My point: if you would switch the relay much slower, which is the way that it is designed to be used, the relay contacts will suffer much less with each on/off cycle. Jun 3, 2021 at 7:47
• Looking in datasheet: Durability: 10,000,000 operations min. (at 18,000 operations/hr) 18000 operations per hour means an "operation" every 200ms. That's much longer than your 8.3 ms. Also note how the contacts switch a DC current in that test. Jun 3, 2021 at 7:50
• If you want to switch loads constently, you'd rather use a mosfet based switch like a static relay as mechanical relay will fail eventually. Jun 3, 2021 at 8:37