Original PIRs Stop Smart Light Switches Working

[New Forest Giles]

Here’s a problem I’ve hit when installing a no-neutral, 2-gang, smart light switch into an existing 2-wire (UK) wall switch enclosure, which has PIRs wired in parallel:



When either of the PIRs (motion sensors) are triggered, this effectively shorts the two poles of the smart switch, so there is no voltage across them, hence they de-power and lose connection with Wifi / smart hub. Is there a work around to maintain power to the switch, hence keep it connected and allow the other gang to be operated?

I’ve seen this problem posted in a couple of forums, but no solution has been forthcoming...

 

[MassiveJim]

No, smart switches aren't designed to be used in tandem with normal switches.
You would need to find a compatible smart PIR.

A smart PIR would work with the smart switch and send a signal to the switch to turn on when it is triggered.
I achieve this in my house with Samsung Smartthings.

 

[New Forest Giles]

OK, I've replaced one of the original PIRs with a smart PIR & setup a rule to activate the smart switch. It kind of works, but there's a 1 to 5 sec delay between the smart PIR sensing movement and the light coming on, hence I've usually left the room again before it activates. I'm guessing this is because I'm not using a local hub, hence the signals are going to the 'Smart Life' app servers in China. Also this app only allows a minimum of 110 sec countdown when really I only need the light on for 10 sec as I walk through the room.

 

[MassiveJim]

OK, I've replaced one of the original PIRs with a smart PIR & setup a rule to activate the smart switch. It kind of works, but there's a 1 to 5 sec delay between the smart PIR sensing movement and the light coming on, hence I've usually left the room again before it activates. I'm guessing this is because I'm not using a local hub, hence the signals are going to the 'Smart Life' app servers in China. Also this app only allows a minimum of 110 sec countdown when really I only need the light on for 10 sec as I walk through the room.

probably yes. I use Samsung smartthings which uses a local hub and its pretty much instant

 

[New Forest Giles]

Postscript to this discussion:
I eventually found a solution to this problem using a general purpose relay (PY2NJ + PTF08A base ~ £6 on ebay)

Seems to work a treat!

 

[lewism]

Looking at that schematic, would the activation of PIR2 not create the same shorting of terminals and cause the fault to occur? With the relay only being on PIR1?

 

[Pho]

As a slight side note for you, you're using PIRs from Tuya - they make the Smart Life app, and tonnes of smart plugs are just rebadged Tuya electronics and reskinned Tuya apps.

If you want a bit more control you might want to look at running something like Home Assistant on a Raspberry Pi or similar as this has an official plugin from Tuya themselves.

I'm kind of doing the same thing but in a slightly more complex way: I have Hue outdoor motion sensors (running electric cables was hassle) which are integrated to my HA set-up so it pings it when there's motion, then I have a rule set-up to trigger a few different smart switches (Tuya ones) for ~5 minutes which are connected to outdoor floodlights.

The reason I did it this way rather than just buying a floodlight with PIRs built in was that I wanted motion at the front of the house to trigger floodlights at the back etc, and this would've been a pain to wire with traditional PIRs and no smart plugs.

 

[New Forest Giles]

Hi lewism - The double smart switch I have only seems to draw power from the left-hand S1 switch to operate (hence the capacitor on that circuit), so I only needed to install one relay.

 

[lewism]

Hi lewism - The double smart switch I have only seems to draw power from the left-hand S1 switch to operate (hence the capacitor on that circuit), so I only needed to install one relay.

I seen the capacitor but didn't understand why it was required in parallel with L1 but not on L2. Is this something that you added in yourself on the circuit? If so where did you add it? (As in its physical location)

I would wonder if it's due to the electronics in the dumb PIR causing issues with the electronics in the Smart Switch as you never reported this fault with the smart PIR, just the delay? That would suggest to me an oversight on the smart switch manufacturers part as a set of clean contacts inside the smart switch would solve this issue.

I'm an electrician rather than being in to electronics but it's still interesting none the less.

 

[New Forest Giles]

I purchaased a number of these no-neutral single, double & triple 'Smart Touch' light switches last year and they all came with a 0.33μF capacitor plus instructions to place them in-parallel with the load on the S1 (left-hand) switch. This YouTube video goes some way to explain how these no-neutral smart switches work & why a capacitor may be needed to allow a transient current to pass.

The existing dumb PIRs are just that, simple on-off switches. I did try a Smart PIR (see above), but this entailed no aditional wiring, as it was battery powered.

 

[Semple]

As a slight side note for you, you're using PIRs from Tuya - they make the Smart Life app, and tonnes of smart plugs are just rebadged Tuya electronics and reskinned Tuya apps.

If you want a bit more control you might want to look at running something like Home Assistant on a Raspberry Pi or similar as this has an official plugin from Tuya themselves.

I'm kind of doing the same thing but in a slightly more complex way: I have Hue outdoor motion sensors (running electric cables was hassle) which are integrated to my HA set-up so it pings it when there's motion, then I have a rule set-up to trigger a few different smart switches (Tuya ones) for ~5 minutes which are connected to outdoor floodlights.

The reason I did it this way rather than just buying a floodlight with PIRs built in was that I wanted motion at the front of the house to trigger floodlights at the back etc, and this would've been a pain to wire with traditional PIRs and no smart plugs.

If you want to hardwire the floodlights, take a look at Shelly. They do a Smart relay which is good for 16amps, has local control too.

 

[New Forest Giles]

I hope to take a look at the Home Assistant ecosystem in the coming months to better understand what it can do.
I'm familiar with the Shelly devices and already use a couple of the Sonoff equivalents.