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I have existing led lighting in my garage 240 v ac which operates from a pull switch. My garage door opener provides a facility to power a light with 240 v ac as well. What if any additional circuitry, if any, would I need to add if I connect the garage door opener to the same light to cover the situation where both supplied power at the same time?

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    I take it your mains voltage is 240 not split 240/120 that is used in the U.S. – Ed Beal Aug 13 at 21:35
  • Where are you on this planet, and is this pull switch integral to the fixture, or separate from it? – ThreePhaseEel Aug 13 at 22:39
  • I am in the UK so its 220-240 volt ac single phase. The pull switch is separate from the lighting. I guess what I am asking is what is the effect of connecting two power sources at the same time and how can I prevent this if its bad. – user1759818 Aug 14 at 12:51
  • Can you mount something like a RIBH1C at your pull switch? – ThreePhaseEel Aug 14 at 23:43
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If I've understood correctly, you want the existing lighting to turn either when the pull switch is activated or when the door opener is activated.

To accomplish this use a relay. The relay's coil would be powered by the door opener and the relay's switch terminals would connect to the terminals of the existing switch. In this way the light will be powered from its existing source whenever the pull switch or the relay (or both) are activated. The relay protects against a variety of bad results that could occur if the door opener output had been connected directly to the pull switch or lighting.

You'll have to choose a relay with appropriate voltage and current specs, and consider local requirements and customs to choose a junction box to contain the relay and wiring. I'd suggest that the relay should be located as near to the pull switch as possible.

schematic

  • Notably, the garage door "lamp" can go straight to a 24V transformer. The 24V wire runs between the opener and the relay's coil, which would need to be 24V to match. Being low voltage, the rules for wiring are significantly relaxed. Instead of jury rigging a 24V transformer, you could use a simple cell phone charger block screwed in with an adapter, and pull the 5VDC out via a USB cord you cut down. – Harper Aug 13 at 22:08
  • That said, this drawing could be improved by fudging physical locations to reflect best wiring practices, i.e. Relay right next to switch. – Harper Aug 13 at 22:09
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Greg has the crux. I'm only going to talk about packaging.

I gather the pull switches are inside the LED lights. I would modify each LED light as follows:

  • I would affix two-terminal low-voltage screw terminal blocks to the outside of each LED light, and put a label that says "Apply 5 VDC to bypass pull switch and turn on light".

  • I would get a 5V relay with contacts rated for tungsten load at least as large as your LED light (1 amp should suffice).

  • The coil of the relay is wired with #18 wire to that external terminal block.

  • The "NO" contacts of the relay are wired to both sides of the pull switch, so it is in parallel with the pull switch.

  • Now if you apply 5 volts to the external terminals, the light comes on.

At the garage door opener, I would unscrew the light. Then I would install a common "Edison E26/27 to NEMA 1-15R" screw-in adapter that turns a light bulb socket into an appliance socket. Then I would install any common cheapie USB cell phone charger block that works on 100-240V and yet has a NEMA 1-15P plug into that adapter.

I know I'm sending you on a snipe hunt to find NEMA 1-15 gear, but NEMA 1 is the only mains socket that will fit inside an Edison E26/27 socket.

As of now, when the garage door turns on the light, you can charge your phone LOL.

Then I would get any competent USB cable and cut it midway. Find the wires which connect to the outer two USB terminals. Splice those to #18 thermostat wires, and distribute that to each of the LED lights.

  • Those are great enhancements to the idea, especially if the lights each have their own switch rather than being controlled by a single switch. The suggestion to use an off-the-shelf USB power supply to get away from mains voltage and simplify the wiring methods is both clever and elegant. – Greg Hill Aug 13 at 22:35

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