WEMO Hardware

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Posts: 1
Registered: ‎02-13-2017

Zero Crossing - do the plugs have it?

Do the smart mini plugs have zero crossing relay/SSR circuit inside?


Zero crossing means that power is turned on or off synchronized with the AC signal such that it minimizes disruption of the thing being powered. I'm thinking of turning on and off a subwoofer amplifier which is somewhat sensitive to power condition when turned off. It can make a loud whomp if it's not zero crossed.


I can just try it of course, but it would be good to have this technical question answered definitively.



WEMO Maker Inventor
Posts: 1,562
Registered: ‎06-14-2014

Re: Zero Crossing - do the plugs have it?

Wemos use mechanical relays to switch the line current so no different than powering on with a regular lightswitch.

Posts: 320
Registered: ‎05-04-2015

Re: Zero Crossing - do the plugs have it?

[ Edited ]

Mike's quite right, braddo.


It's just a case of switching on at any angle of the waveform of the mains. It's usually an issue (if at all) at switch on though, but an amplifier could indeed produce a loud thump at switch off.


At switch off it's perhaps more likely due to an RF spike coming from the relay contacts when switching an inductive load, in which case a line conditioning capacitor might help. You can get one at your local domestic appliance repair shop as they use them to suppress interference from motors and switches and so forth.