Smart switch no neutral issue Featured

Some no-neutral smart switches acquire power by trickling current through the load, which gives them enough voltage drop to scavenge power. That only works with a filament bulb because you can't trickle through a fluoro or some forms of LED PSU. Have you changed the LED recently?

Otherwise I think they try to harvest power when the light is on, when there's enough current flowing to cause a voltage drop, and store that in a supercap. That only works if the light is on regularly enough to charge the supercap.

I suppose putting a cap in series with the load might act as a capacitive dropper and also offer some voltage drop.

The one variable here is the LED driver, which is something the switch doesn't know anything about. All this trickling and dropping only works if the load will allow current to flow. Maybe your switch and tube combination are incompatible? Maybe there's something about fluoro-replacements that make them look different from bulbs?

Unfortunately no-neutral switches are a hack at best, so it might be trial and error to find something that works. A filament should, but I don't know about fluoros or fluoro-replacements.

Or get one with a battery that doesn't need to scavenge power?

Theo

Thanks for that. It's a little frustrating as until it decided to not work, the one I had in place worked fine for 6 months. Hopefully I will get an identical one from the vendor in the new year.

I'm not too bent out of shape as the one I'm trying now was less than £8 from China in 6 days.

I agree the LED drop-in replacement for the fluorescent tube is the unknown quantity here. All my other smart switches work fine with no neutral and "regular" LED lamps.

Is the the sort of switch where you push it and the light switches on for a set period of time?

I tried several versions for my downstairs loo with and without a capacitor, but none lasted more than a few months...

.. in desperation I tried an old fashioned pneumatic plunger but that didn't stay on long enough for me to finish the crossword, so in the end I wired the switch permanently on and fitted an infra-red sensor from screwfix.

It can be set accurately and a quick wave will re-start the time should I be struggling with the crossword. Its been there for nearly two years now and still works fine...

Dave

When I re-wired our bungalow I did consider looping in at the switches thus providing a neutral but owing to the fact that the roof pitch is so shallow you cannot stand up in our loft and possibly working in the extremes of the trusses, I opted for running a series of Wago boxes down the spine of the house branching off to the switches and rosettes. The plan being to use Quinetic switches where I want smart functionality by simply removing the switch wire and wiring in a Quinetic WiFi receiver at each Wago box where I need smart functionality and replacing the switch plate with a Quinetic switch this would enable switching either with the switch or Alexa voice control.

Richard

As an update to this:

while waiting for (hopefully) a like for like replacement from the original (works with my LED replacement for fluoro tube), I thought I would try the new switch in a different fitting - with 3xLED bayonet type lamps and no neutral.

Still didn't work.

Annoyingly all my switched lights are LED or LED replacements for fluoros, so options are limited.

Unusually, I must have got lucky with the original design of smart switch for it to work with 4 LED lamps of various stripes.

Replacement switch arrived today.

Idiot courier tried to jam it through the letterbox which managed to shatter the glass cover. Luckily I had the old one so it was an irritation rather than an issue.

Connected it in and it worked perfectly.

Clearly not all "no neutral" devices are equal.