I would like to take the 240V feed from a trailing edge dimmer that is driving LED lamps and use it also to activate a contactor or relay. This would in turn run a 230V fan.

(Reason: want to have a single dimmer switch controlling bathroom lights, but also have the switch turn the extractor fan on. But don't want to send a dimmed signal to the fan!)

I'm worried that the chopped signal from a trailing edge dimmer may not be what the coil of a relay or contactor needs.

Can anyone shed some light on this, please?

Either, will a relay work just fine on this circuit? Or are some relays more tolerant of what activates them?

Many thanks!

  • \$\begingroup\$ Can you get dimmers designed for 3-wire (switched-hot/dimmed-hot) magnetic fluorescent loads? \$\endgroup\$ – ThreePhaseEel May 5 '17 at 3:08
  • \$\begingroup\$ Do you have access to constant undimmed 230 V anywhere near your fan? If so, so can create a circuit from your dimmed output which would switch a relay from said 230 V to your fan. \$\endgroup\$ – winny May 5 '17 at 5:00
  • \$\begingroup\$ Hi ThreePhaseEel, alas no. There have been a few dimmers in the past that offer essentially a two pole output, one dimmed, one switched, but they're hard to come by, and they were never produced with a trailing edge dimmer. The dimmer itself is the main event, and must take centre place. The dimming of LED lamps is so fussy! \$\endgroup\$ – Bagpuss May 11 '17 at 13:58
  • \$\begingroup\$ Hi winny, yes, I do indeed have access to permanent live mains 230V. This is what I plan to use to drive the fan, switching it using the relay! I think what you've described is exactly what I'm trying to do! It's all about activating the relay with the dimmed output. Will the coil of the relay work okay with a dimmed/chopped output? \$\endgroup\$ – Bagpuss May 11 '17 at 14:02
  • \$\begingroup\$ If you give a relay AC it will chatter. It would first have to be at least rectified and filtered, probably regulated too. \$\endgroup\$ – Phil C Apr 26 '18 at 2:27

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