Bypassing Delay Switches

Discussion in 'Electrics UK' started by bigalxyz, 7 Oct 2021.

  1. bigalxyz

    bigalxyz

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    manufacturer has replied to my query, says PIR consumption is 0.5W so that’s (scratches head) 1 unit in 2,000 hours = about 4.5 units per year which will be about 80p per light per year on our current tariff. I think I can live with that!
     
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  3. JohnW2

    JohnW2

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    Yes, if that is correct, then 19 of them should only cost around £13 per year to run, which is pretty trivial. However, even that is probably more than it would cost if you had all 19 lights coming on simultaneously, very occasionally, for a minute or three.

    Another thing to bear in mind (as well as the up-front cost of all the PIRs) is that the PIR electronics does fail. I have half a dozen PIRs in my garden, and I probably have to replace one every year or two - so with 19 it would probably be at least an annual event - and don't forget that if they are 'integrated' (PIR+light) fittings, you would have to replace the whole fitting, not just the PIR part.

    Also, from the practical/safety viewpoint, since you are illuminating a (presumably 'very long') 'long hallway', if you have each light coming on/off independently (under PIR control) part of the hallway would be unilluminated if one of the fittings (PIR and/or light) failed, whereas if all lights came on together, there would still be a fair bit of illumination, even if one of the lights was not working.

    As has been said, if you are unhappy with the (un)reliability of pneumatic delay switches, there are electronic versions (probably easier to find than pneumatic ones these days) which are not so mechanically unreliable.

    Kind Regards, John
     
  4. SUNRAY

    SUNRAY

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    My point is based around the, assumed, capacitive 'voltage dropper'. If it needs to supply 50mA to drive a relay (as in the old unit I checked) the capacitance needs to equate to around 4KΩ and this needs to be followed by someform of voltage regulation, commonly a zener diode. All the time the dc needs to be kept to say 24V that basic dropper system will consume lots of power. One of the sensible design features is to use a higher voltage relay, for example 12V will require 4 time the current of a 48V relay

    However if the maximum current is 5mA as in the triac unit the capacitancors impedance will be around 40KΩ resulting in a much lower power consumption
    AsI mentioned before the idle current is much lower than the old days(y)

    .
     
  5. bernardgreen

    bernardgreen

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    Some of these units use the charge in a charged capacitor to pull the relay in (ON) and then rely on a much lower current to keep the relay held in.
     
  6. JohnW2

    JohnW2

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    If they used a zener to 'regulate' the supply to 'everything' (including the relay coil), there would presumably have to be in excess of 50mA constantly passing through the zener in the idle state - but that would be ridiculous, and I can't imagine that they would be that daft. To regulate the voltage of just the supply to the electronics would only require a tiny current.

    Kind Regards, John
     
  7. SUNRAY

    SUNRAY

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    Indeed it would have to maintain the 50mA so it has not only been done the way I mentioned, however in order to accomodate the 50mA the power section has to be able to cope, generally I've found that means a higher standing current than it could be. As Bernard says there are a nmber of ways to reduce things.

    I have some 'nightlights', big 13A plugs with 3 leds and LDR, they run at 18/19mA idle/on or 4VA (thanks to Plugwash for th correction).
    Hmmmmmm.....

    I keep meaning to get one of the power meter like Big Clive uses.
     
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  9. JohnW2

    JohnW2

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    I nearly forgot this, but have just found a few 'spare moments'.

    I used a very cheap energy monitor (whose only real 'failing', for this purpose, is that is displays power only to one decimal place of Watts). As ca n be seen in the tabulation below, the results I got with various cheap ('capacitive dropper') LED lamps/bulbs and an incandescent lamp/bulb indicate that it is giving reasonable results - with a PF of 1.00 for the incandescent, and roughly 0.4 - 0.6 with the LEDs, lower for the lowest power of the LEDs.

    I then tried with a cheap standalone PIR which I had on my shelf (a spare, since I have several of these in service - see picture of the type below), which has a relay output and claimed power consumption of 'approximately 0.5W'), and got results even more dramatic than I expected, with a PF less than 0.1, and with both PF and power consumption much the dame with the sensor in its 'idle' and 'activated' states.

    So, the bottom line is that the (true) power consumption of these PIRs is trivial/negligible - in the case of my one, something like 6.1 kWh per year for continuous 24/7 (about £1/year at 16p/kWh). That type cost around £8-£10 and, at least in my experience, usually last for at least 5 years (often a lot longer) - so the total cost of having one (initial outlay + running costs) probably amounts to £2 - £3 per year.

    upload_2021-10-19_17-3-36.png

    upload_2021-10-19_17-24-46.png

    Kind Regards, John
     
  10. plugwash

    plugwash

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    Sounds like about what I would expect for a capacitive dropper base solution.
     
  11. JohnW2

    JohnW2

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    If one does the sums, it's reasonable enough - so perhaps the more surprising thing is that the PFs with (capacitive dropper) LED lamps/bulbs are as high as they appear to be.

    Kind Regards, John
     
  12. plugwash

    plugwash

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    I suspect the difference is the LED bulbs are dropping most of the voltage across the LED arrays and only a relatively small amount in the capacitive dropper while the PIR is dropping down to the relay coil voltage (say 24V or so) using the capacitive dropper.
     
  13. JohnW2

    JohnW2

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    If that were true, it would obviously explain the difference, but I didn't think that there were all that many LED elements.

    Do the 'chips' in these bulbs perhaps each contain multiple LED elements (I had assumed that it was just one element per chip)? The 7W one I tested had only 10 'chips' (and the 12W one had 22 'chips').

    Kind Regards, John
     
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