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Posted by terry on September 20, 2007, 4:15 am
> the secret is if the output switching device is a relay,
> thermal relay, or a solidstate device.
>
> You can tell by the wiring, relay/thermal relay is operated
> from the AC line and will have THREE wires, black(hot),
> white(neutral), and red(lamp load). It will directly
> connect the red to the black when "dark", you can hear a
> relay "click" but the thermal relay will be silent and
> delayed as a small heater heats a bimetal set of contacts.
>
> Without being connected to anything, an ohmmeter will show
> the black and red to be a direct short. the photo cell only
> powers the relay while in daylight, the relay actually
> "opens" the contacts, turning off the light. backwards from
> what you might have expected. they also usually have a high
> current rating like 15A.
>
> Solid state devices are TWO wire, black and black, or black
> and red. It is wired in SERIES with the hot line and the
> lamp. This creates two problems, while "off" the cfl isn't
> enough of a load to provide the few volts the ss device
> needs to properly operate. This causes the output to pulse
> on and off, beating the crap out of the cfl until it fails.
> And even when "on" the cfl can't provide a stable voltage to
> keep the ss device in "on" mode while operating, sometimes
> only providing half wave DC to the cfl.
>
> Cfl's only like fullwave AC power fully "on" or completely
> 'off'. Anything else and the two fight each other until the
> cfl just fries itself. these devices will have a minimum
> wattage(load) like 5-20 watts, and a maximum like 600 watts.
>
> There are ways of making a "safe" ss device that switches
> just like a relay, but that would require 12 components vs
> the 4 used now, and there MUST be a neutral wire connection.
> And no one would pay for them ;-)
>
> -larry / dallas
Thank you very much indeed to Larry and others for the detailed info.
Learnt a lot. The comment about insufficient load through a 'ss only'
device makes sense; similar to solid state programmable thermostats
that specify a minimum of say 500 watt heater load to ensure enough
voltage to operate the device.
Ours sensors controlled fixtures do indeed 'click' (you can hear them)
so figured there was relay in there and relays don't like inductive
loads very much, cos sparking at the contacts erodes them. But we are
switching AC here anyway (not DC through say an inductive load!).
Again ours with black live and white neutral 'in' and red switched
live 'out' also seems to confirm that they are a relays.
Also realised that the sensor alone would make a good security device
to set off an alarm. Think I'll acquire some more of these devices!
Many thanks for the useful discussion.
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