I'm controlling 4 Relays(10A) with a controller. While randomly switching it without zero-cross my controller gets restart. To avoid this I'm switching relays at the zero-cross point, But my question is every relay had the different operating time(on time) and different release time(off time) in the datasheet.

Should I add these times with zero-cross detect time or directly switch relay whenever zero-cross occurred.???

Little bit confused with these time durations, Can anyone explains how to use zero-crossing for relays switching exactly???

  • \$\begingroup\$ If this an electromechanical relay? If so, I do not believe electromechanical relays are fast enough, or consistent enough to switch at a zero-crossing even if you sent it the right signal. \$\endgroup\$
    – DKNguyen
    Aug 8, 2020 at 16:29
  • \$\begingroup\$ @DKNguyen I'm not switching it consistently at every zero-crossing. I'm switching it randomly but want to reduce EMI from it. \$\endgroup\$
    – ravi teja
    Aug 10, 2020 at 10:09

1 Answer 1


While randomly switching it without zero-cross my controller gets restart

That's a susceptibility weakness of your controller.

To avoid this I'm switching relays at the zero-cross point

Sounds like you intend to swallow a spider to catch a fly. Where does this stop I wonder?

Use this opportunity for improving the EMI rejection of your controller. The controller (any controller) should not be susceptible to this. Fixing your controller is the best long-term advice you will get.

Should you not heed this advice and one day you are presented with a load that is inductive in nature, instead of switching at the voltage zero-cross you will need to switch at the peak of the voltage (where the current passes through zero).

And, if you do decide to press ahead with synchronizing the switching then, it would be better to switch at the load current zero-cross. Of course, you may have been planning to do that all-along but, your question wasn't clear. Take into account both switching times and, if it's 10 ms (for example) then begin switching 5 ms before the zero-cross.

You might also consider that when switching off you shouldn't use a diode clamp on your relay but a zener/diode clamp to ensure the off-speed is minimized.

  • \$\begingroup\$ Thank you for your response. My intention of using zero-cross, to reduce EMI and to extend relay life. \$\endgroup\$
    – ravi teja
    Aug 10, 2020 at 11:51
  • \$\begingroup\$ @raviteja are you done with this now? Do you need more clarification on anything? \$\endgroup\$
    – Andy aka
    Aug 10, 2020 at 12:08
  • \$\begingroup\$ Yeah, It's done. \$\endgroup\$
    – ravi teja
    Aug 11, 2020 at 11:13
  • \$\begingroup\$ electronics.stackexchange.com/questions/368461/… This one helped me from reboot \$\endgroup\$
    – ravi teja
    Aug 11, 2020 at 11:16

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