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Bypassing Delay Switches

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

  1. bigalxyz

    bigalxyz

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    True, although on the other hand it’s often the case currently that only one or two lights are really needed and yet currently they all come on (19 of them) so there must presumably be a decent saving to be had by having each light controlled by its own PIR sensor - so that only the lights that are actually needed are lit up.
     
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  3. JohnW2

    JohnW2

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    Well, for a start, "having each light controlled by its own PIR sensor" would presumably require the purchase of 19 PIR sensors, and it would probably take a long time (if ever) for that up-front cost to be recovered by reduced electricity usage (if any).

    Remember that, as winston said, each PIR may well cost around £4-£5 per year to run, so around £76 - £96 per year for 19 of them - so that could well cost more than letting all 19 lights come on together.

    Kind Regards, John
     
  4. bigalxyz

    bigalxyz

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    True, but the current setup is in a sorry state (long story). The delay switches don’t work well and more than half of the existing lights don’t work either - so we’ll need to replace them with *something*! The bulkhead lights with PIR can be had for £18 which is a bit more than a non-PIR light but if it means we can get rid of the delay switches (which are always seizing up & have never worked well), I’m ok with that.

    gonna try to find out the power consumption of the PIR sensor when switched off anyway, just so that I know what to expect.
     
  5. EFLImpudence

    EFLImpudence

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    You can get electronic timed switches - possibly, depending on the wiring method, with only one timed switch and the rest just momentary switches which activate the timed one.
     
  6. SUNRAY

    SUNRAY

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    My apologies, I totally misread the original post and now removed mine.
     
  7. SUNRAY

    SUNRAY

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    I think your 3 watts may be out of date now but the sentiment is spot on. I'd like to think the newer sensors are more like 1W these days.

    A while back I was doing some controls work in an office building, 5 floors with ladies and gents toilets on all, each had a light in a lobby with a switch, over the basins with a switch and over both cubicals sharing a switch. First person in the morning would switch all 3 on and cleaners would switch off as they finished.

    This was long enough ago now to forget actual weekly figures but it goes something like:
    4x 7W CFL x 12 hours x 5 days = 1680Wh... x 10 toilets = 16800Wh or 16.8kwh

    After fitting 3 PIRs in each toilet:
    3x3W x 24hrs x 7 days = 1512Wh for PIRs
    4x 7W CFL x 6 hours average x 5 days = 840Wh
    Total = 2352Wh.
    Net increase of 672Wh per week x 10 toilets = 6720Wh or 6.7KWh or 40% increase for the building.

    I have overcooked the figures as I don't recall it being this bad.

    The electricians employed to do the survey/report and cost saving work were challenged and I believe not paid but we got paid to remove the PIRs and fit new switches, fortunately no wiring had been removed.


    With the economy of LEDs now I'm finding some places are leaving lights on 24/7 or using a single dusk to dawn sensor to control large areas of lights.
     
  8. JohnW2

    JohnW2

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    Yes, we/you really need to know that - as SUNRAY has said, winston's 3W per PIR may be pessimistic in terms of modern units. However, I nevertheless suspect that 19 of them would very probably consume more electricity than they saved, even if appreciably less than 3W each.

    Kind Regards, John
     
  9. SUNRAY

    SUNRAY

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    I've just measured 2 units, the 10+ years old is 14/67mA (3.2/15.4W) and the new one purchased July 6.9/19.9mA (1.6/4.6W) at idle/relay operated.
     
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  11. JohnW2

    JohnW2

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    Thanks. Even 1.6W (idle) is around £50 per year for 19.

    Kind Regards, John
     
  12. SUNRAY

    SUNRAY

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    And another with triac switching: 4.3/4.7mA (0.99/1.08W)
     
  13. JohnW2

    JohnW2

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    That's presumably just 'co-incidental', since whether the switching is by relay or triac should not alter the 'idle' power consumption - in other words, this ~1W (idle) one probably just has 'lower power' electronics than the 1.6W one, regardless of how the switching is done when it is activated.

    Kind Regards, John
     
  14. SUNRAY

    SUNRAY

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    I assume that's the case, based around not needing to cater for a high power device (the relay).
     
  15. plugwash

    plugwash

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    It's also worth pointing out that you can't just multiply voltage by current to get power, if the PIR is powered by a capacitive dropper it may have a very low power factor.
     
  16. JohnW2

    JohnW2

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    Indeed. Although the 'driving' semiconductor, or semiconductor element, obviously has to carry a much higher current in the 'activated' state in the case of a relay (as compared with a triac), it should be totally 'off' (no current, hence no power consumption) in the 'idle' state in both cases (i.e. even if there is a relay).

    Kind Regards, John
     
  17. JohnW2

    JohnW2

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    Good point. If I have some spare moments sometime, I will try to 'do the experiment'!

    Kind Regards, John
     
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