PIR (standalone) with LV transformer ok?

Paul wrote on Tuesday (06/01/2004) :

Hi Paul,

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.

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 > >

Thanks Harry.

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...

Paul.

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.

On 06/01/2004 Paul opined:-

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.

On 06/01/2004 snipped-for-privacy@hp.com opined:-

The easy way to tell which is which, is to trigger the PIR and if it clicks you know for sure it is a relay type.

Hi Been there done it , And it works fine, Been in place for about 8 months now with no problems.

Ian

Hi Dave,

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

I will wire it all up... and see how long it lasts...

Paul.

Hi

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.

Ian

Are you thinking of using a 230VAC coil on this relay?

Christian.

I would bet that it does have a relay.. The relays they use are quite small, the size of a large rectangular capacitor.