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It's just a surge limiter, you would need information from the unit manufacturer to identify the one they used, but it's usually not at all critical.
However, it only seems to be feeding a zero-crossing detector, so there shouldn't be any surge anyway?. What values are the two resistors feeding the opto-coupler?
It's in series with the rectifier feed to an optoisolator, not a power system.
It appears to be a VDR that could be used as a voltage dropper for that, ensuring a long turn-off around zero crossings? Or possibly some kind of an "early power fail" brownout detector circuit.
If the welder is for 230V, I think the VDR should have a breakdown voltage (not AC working voltage) of around 80 - 120V.
That will split the power dissipation between that and the 22K, RZ105.
Thank you for advice. I think I understood how it works. This welder is for 230V, but I dont know what voltage I should take to account, Urms =230V or Upk=230*1.41=324V.
Typical value of input forward voltage for couple CNY65 is 1,25V.
Neither, exactly - it appears the voltage should be split over the VDR and the series resistor. The current to the opto isolator LED will peak at around 6 - 7mA or so, then.
As I suggested, try a VDR with a breakdown voltage around 100V or so.
Something like this should be reasonable, to see how it works?
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