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Optocouplers for mains? Answered

I would like to know if i can use an optocoupler instead of a regular relay?
Like on one side would be an arduino and on the other would be 220 v ac to control a  light for example
Is this setup possible?



Best Answer 4 years ago

Yes !
Here is a circuit that uses any uP output pin.
to turn on an incandescent light bulb.



BTW  the 470 ohm resistor does not need a lot of power.
That is because as soon as gate current flows
the Triacswitches into conduction and
there is no more voltage across the power pins::-)

Brilliant , so can i use the MOC3023 and the bt137 with the 470 ohm to switch mains ? 200v upto 10 amps?

sorry 220v 10 amps and also what about fans , like a ceiling fan , can i use the same setup to control that as well?

The MAC12 with 12 amps RMS is better then the BT137 at 8 amps RMS. It will take 65 amps start up serge but the BT137 will get hot at a constant 10 Amps.

Thanks , i did a little research and i found out something about a snubber circuit , do i need that for a ceiling fan ? what about a table fan?

If there isn't one in the fan already yes. Some adjustable speed fans have snubber circuits in them.

It is worth understanding what a snubber circuit does for this triac.
  • All semiconductors have peak voltage, peak current, dv/dt and di/dt limitations
  • A Good design takes care of peak voltage and current.
  • BUT dv/dt which is a momentary transient raise of voltage
  • Can and does turn on a Triac when you don't expect it to.
  • A snubber will prevent or absorb excessive dv/dt protecting the semiconductor from a transient power line condition.
  • This is why hand drills must have a mechanical disconnect at low speed end.
  • You would not enjoy !! the shaft suddenly turned while changing a drill bit !!!

Oh my last question , Say i use the MOC3023 and the BT137 , what can be the maximum limit i can push this system to before it causes any problems?

Well your mains are 220 AC volts so the BT137-500E should be fine it is 8 amps RMS (running current) and 65 amps surge or start up current.

As long as you do not run it for a long time over 8 amps it should be fine.

The MOC3023 is also fine for running the BT137-500E

You can get the datasheets here:


Yes you can control a ceiling fan !
and with no annoying relay clicks
or sparks that could cause a fire.

A Triac optocoupler like a MOC3010 to a Triac like BT137 will do 8 amp RMS or a MAC12 for 12 amps RMS.

The finish Triac current and gate current are your challenge.

I would like to thank both of you for taking your time to clear my doubts and explain what i didnt understand
Thank you