Wireless Switch with 2 Dimmers and Load incompatibility

Hi There Gurus,

I have a problem with a Wireless switchplate (2 dimmer) location that is driving two circuits.

The only place these two circuits appear is near the front door. One is a lounge area circuit and has no problems, but the other is an outdoor light which is currently an Arlec style Sensor Light.

Though noting the may or may not work issue to the client prior to install, I thought this would probably still be OK if I just set the dimmer to act in On/Off only mode. This actually works fine for turning the light on and off but the sensorlight needs you to turn it on, then off for five seconds then back on to set up the Sensor triggering mode. The problem lies (I think) in that the Off isn't Off enough as there is still power flowing for the normal filament pre-heat. So you can't get it into sensor trigger mode (without using the circuit breaker off method ).

I am now contemplating using a 240VAC Contactor on the dimmer using it to switch the light circuit fully in and out. Do you think this will work or will the Relay load be in-sufficient for the triac and it think the bulb has blown and shut it down?

Is there another way you can suggest (there's no wired C-Bus network access nearby for a 5750WPL sensor)?

Your thoughts appreciated,

Brad

 

The dimmer channels will always have a small amount of current passing through them (about 1/2 a watt total for dimmers), even when off, due to the EMC filter components, and also for powering the unit's internal electronics. Remember that there is no neutral, so the unit has to harvest power from the small amount of power trickling through the load, even in the off state. It sounds like the continual trickle of power is enough to make the Arlec motion sensor think that power has not been turned off.

It might be a case of just having to wait for more than 5 seconds. Try giving it a few different longer time intervals to see if it's enough for it to discharge sufficiently.

Another option might be to fit a bypass capacitor (Clipsal 31CAP or a 470nF X2 type, for example) in parallel with the Arlec sensor light to help bypass the sensor light when the dimmer channel is off.

Connecting contactors or relays to dimmer channels can be quite hit-and-miss. The dimmer is a 2-wire type (no neutral), so full brightness is actually a little less than full conduction, and this can make the relay/contactor windings hum/buzz and heat up. If your dimmer is a Leading Edge model there will also be a voltage spike when the dimmer turns off (as it does not go to 100% conduction) which will shorten the life the various electronc devices. On the opposite end, when the dimmer channel is off the bleed current may prevent the relay/contactor from un-latching reliably. A third possibility is, as Ashleigh says, the contactor might not provide sufficient load to the dimmer, and the unit may run out of power and reset itself.

If you don't have any success with the longer time interval or bypass capacitor options you can replace the 2-channel dimmer with a 2-channel relay. The second channel of the 2-channel relay features a proper micro-gap disconnection, such that off is really and truly off (there is a little Mu character on the product label adjacent channel 2 to indicate this, which you can see on page 13 of the Installation Instructions). If you connected the light circuit to channel 1 and the sensor circuit to channel 2 then you should be able to achieve what you want, minus the dimming.

 

Hi Newman,

Thanks for the options. I will give them all a try and report back. I think the capacitor idea is probably the best one if it works as I suspected the 'brute force' contactor approach would have a few thorny issues which you seem to agree with.

Unfortunately the other circuit is the main lounge room downlight and so relays would not be viable. I would run a C-Bus line to a 5750WPL before removing the client's main lounge dimming!!

Many Thanks,

Brad

 

Hi NickD,

I like your thinking ..... but unfortunately the conduit behind the wallbox is too thin!!

I suppose I could mount the light on an enclosure and put the relay inside but that might look a bit odd, but would work as a last ditch effort. But does the plug adapter relay share the channel one design from the switchplate? (ie still leach current through the load)

To be honest I think I would battle through running a C-Bus cable to a 5750WPL before that though.

Thanks for the idea though.

Brad

 

The plug adaptors are quite different as they have both active and neutral available through the 3-pin socket, and therefore they have no need to harvest power from bleed current through the load. Off is still not completely off as the EMC filter components still allow a tiny amount (> 0.1W) of power to bleed through the load but that may well be low enough for your arlec sensor to think that it's properly off. In fact if you're going to install a plug adapter you might as well use a relay version.

 

Thanks Newman,

Brad