I have a LV light in my outside porch canopy (IP56 before anyone screams)
and as the builder (its a new house) has yet to install a streetlight, I
would like to put a PIR on it, so that any "visitors" during the dark hours,
get a nice welcoming light to invite (or repell) them as required.
I got a standalone PIR from screwfix (11291), which is about 2KW for
standard lights, there is another lower rating (which I cannot recall) for
energy saving, but there is no rating for LV lighting.
I have a 60W LV transformer from screwfix, and its definetly an electronic
type (as oppose to a standard wound coil) - Question, will this fry the PIR?
PIR seems to be solid state, I am worried about the effect the electronic
transformer will have on the device... its temping to try and see for
£8.99... but if I go to the effort of installing it and it pops a week later
I will not be amused!!!
Anyone ever tried this?
The problem is inductive loads are much worse to switch than resistive
ones. Contacts for inductive loads therefor have to be derated.
Were you switching a transfomer type LV light, I would advise caution
in the the rating of the PIR's contacts, but as it is an electronic I
suggest there will not be a problem. Set the PIR's time to a sensible
on time, to avoid repeated triggering.
I was wondering if it qualified as an "inductive load" - which the PIR is
rated at something like 500W from memory (derated from 2000W). I am always
wary of these things, I imagine its a load of circuits and some oscillator
arrangement qith a few capacitors etc that brings power down to 12v, and I
can see it giving a large back spike when it powers off...
I was going to have a pretty long time on the "light on" setting, as the
canopy will be very cold at night, and whilst I got a longer life 4000 hour
bulb, I am sure that I can substantially reduce that with a good bit of heat
stress on the bulb!
I will give it a go, and if it dies, I will buy a replacement and a sutible
size 230v relay from Maplin...
An ordinary lamp bulb is an almost entirely resistive load. The
electronic unit you describe is actually a switch mode power supply
unit SMPSU. Whilst these do have some element of reactive load, it will
be tiny by comparison to that of a motor or transformer. Personally I
wouldn't have any concerns about it.
In uk.d-i-y, Paul <paul at javajedi dot com> wrote:
Almost certainly it'll be totally fine. The PIR's switching element is
unlikely to be solid-state anyway: all the cheapie PIRs I've had, from
Screwfix and other places, have used a relay as the final switching element.
Go ahead, suck it and see.
Since the PIR you have is a "fullfeed" (N & perm L in, switched L out),
you won't even need to use the trick of putting a low-wattage ordinary
incandescent bulb in parallel with your electronick/low-energy load, which
is sometimes necessary/useful for getting in-line dimmers which connect
only in the L line to work with "electronic" loads.
Good luck - Stefek
Great, thanks Stefak.
If it dies a death, I will let you all know!
note: I was sort of impressed with the deisgn - which it sounds like you are
familiar with! It means you can use it on the feed already in place (from my
builders) leaving the switch on 24x7 indoors, but if you are having a party,
or want the light on, you flick the switch and the PIR senses it, and stays
on until it gets light. Very impressive for a 9UKP sensor!
As mentioned earlier I have a LV pir setup, this is for use inside.
Our porch light is a bit of a hybrid using a light sesitive switch and a
timer, This way the porch light is on from 3pm to 11.30pm and 6am to 9.30 am
but only comes on when its dark enough.
"Paul" <paul at javajedi dot com> wrote in message
If you were using an LV transformer, you'd need to know its VA rating, as
this takes into account the inductive nature of such things.
If the PIR is suitable for low energy types as well as normal lamps, then
it probably means it has a relay switching the output. And no 8ish amp
relay I know of couldn't cope with *any* sort of 0.25amp (60 watt) load,
so you'll be safe enough.
*Why is it called tourist season if we can't shoot at them?
Dave Plowman firstname.lastname@example.org London SW 12
60VA I guess, as its 60W... its not a lot, and only has a 35W bulb on the
south side of it anyway...
Hmm, yes I see what you mean. Actually, thats why I asked the question, as I
am pretty sure there will not be a relay (I have not plugged it in yet, I
might be lying) due to the size of the space I cannot explore not really
being big enough to house a sensible 230V relay. I am quiet happy (as the
canopy is hollow and space is not an issue) to get a mains relay from maplin
or RS and connect it between the PIR and the transformer for the light in a
weatherproof box: bit it all seems overkill if the PIR will cope, its only
35W for goodness sake!
Oh, and if I have a relay, then I have to find my bag of Diodes to solder
accross the relay coil contacts and stop the spike from the solenoid
disengaging from blowing up the PIR electronics... and I don't know where I
left them... ;-)
I will wire it all up... and see how long it lasts...
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