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Looking for mains latching timeout relay to prevent water pump flooding

Discussion in 'Electrics UK' started by lardconcepts, 18 Sep 2018.

  1. lardconcepts

    lardconcepts

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    I would like to replace the relay which triggers a water pump, with a relay which times out after, say, 10 minutes. And if it times out, it stays locked out until reset.

    Needs to be 230v AC on both sides of the relay.

    If it doesn't time out, the next time it's triggered it should come on normally.

    I've spoken to everyone from RS to Farnell, and they have everything but. I even found a specialist called Quasar who were very helpful, but again, had everything but, although these came close... https://quasarelectronics.co.uk/Category/kits-modules-multi-mode-delay-timers

    I've got about 10cm by 12cm space to replace the relay currently inside the box.
    Some pics here: https://photos.app.goo.gl/18RiWUcP5Hz9dCo29

    Yes, I know I could probably roll my own with an Arduino, but if it all went wrong, not sure what the insurance would say!

    I've posted more on the plumbing side over in this thread if you're interested in the application.
    https://www.diynot.com/diy/threads/problems-with-float-switch-in-header-tank.509127/
     
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  3. EFLImpudence

    EFLImpudence

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    You are overthinking everything.

    Just get it all working as it should with new float switch. Have two in series if you want.
     
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  4. lardconcepts

    lardconcepts

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    D'oh! That's so simple! I think that would do - I just liked the idea of a third line of defence - mechanical (switch), plumbical (overflow) and electrical (timeout relay)
     
  5. ericmark

    ericmark

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    Off delay relay should do it, don't understand why RS have a problem. However also would go for second float which turns off and raises an alarm.

    We use to say more than 3 timers then fit a PLC. And yes a PLC will do all you want, but to me over engineering the job.
     
  6. lardconcepts

    lardconcepts

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    Yeah, I can find loads of off-delay relays. The trick is finding one which locks-out until manually reset, if the delay is reached.
    In other words, if the float switch is still apparently requesting water more than 10 minutes after it was first triggered, then something is wrong.

    I just thought of another benefit...

    But if someone leaves a tap on or a pipe bursts elsewhere, the tank will just keep on feeding the flood until someone arrives home. But if it's cut out after 10 minutes, the damage is reduced!

    I knew there was another reason!
     
  7. EFLImpudence

    EFLImpudence

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    What damage?

    The damage was caused by a blocked overflow.


    The same could be said in all houses with tank when tap left on, broken pipe or the ball vave fails.

    It depends how much you worry. What if your timer fails?
     
  8. lardconcepts

    lardconcepts

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    Well if, for the sake of £10-£20 I could do a drop-in replacement of a relay without a timeout relay, that just adds another level of protection.
    It's like saying "why have an RCD? What if it fails? Why put a seatbelt on? What if it fails"?

    Belt and braces?
     
  9. EFLImpudence

    EFLImpudence

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    I did say "It depends how much you worry".

    Some do indeed advocate two RCDs.

    Belt, braces, piece of string, anti-gravity machine, another belt, keep hands in pockets.
     
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  11. JohnW2

    JohnW2

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    Where's bernard?
     
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  12. flameport

    flameport

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    There isn't a single device, but that functionality can be obtained from an on-delay relay and another latching relay.

    Latching relay contacts switch the power to the entire system, when closed, things work normally.
    The on delay relay contacts power the coil in the latching relay.
    In normal operation the on delay relay never reaches the on position. If it does, it powers the latching relay coil which disconnects power to the whole system.
    Reset is a separate momentary switch which will power the latching relay coil, switching it to the on position again.
     
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  13. ericmark

    ericmark

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    If a float is asking pump to run after 10 minutes it is also asking pump to run after 20 minutes once the pump has stopped running due to time out so no need to latch.
     
  14. bernardgreen

    bernardgreen

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    As I posted in your other thread there might be a suitable switch in the Kari range of float switches. Depends on the size of the tank.

    https://www.kari-finn.fi/index.php/En/products/float-switches/miksi-kari-pintakytkin-en

    They, together with a simple self latching relay or contactor, are a very reliable way to control liquid levels in a tank.

    It looks like this switch responds to a low float by turning the pump ON ( are there two cables or two single wires coming from that switch

    0x23.jpg

    and this switch responds to normal high water level by turning the pump OFF

    0x22.jpg

    The red mark highlights debris in the hinge of the switch which may have prevented the float rising far enough to operate the switch. There is a magnet in the float which operates the switch when float and body are in line. It is not a good idea to use this type of switch with the float below the body and water lifting the float up to the body.. They are more reliable when the water lifts the float away from the body.

    Or the black box may contain two switches , low level START and high level STOP.

    The answer to using a timer to limit pump run time could be complicated if in normal use the flow from the tank is greater than the rate the pump can supply and flow from the tank runs for longer than the pump's allowed run time.

    Can the pump be allowed run into a closed pipe ? If it can then fitting a standard ball cock to the tank would be a way to prevent the tank over filling if the pump control system fails
     
  15. lardconcepts

    lardconcepts

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    Thanks for the fast replies - sorry, I was away yesterday!

    Thanks for that - would this suit for the delay-on timer? The voltage, price and functionality seem right!
    https://quasarelectronics.co.uk/Item/cebek-i-137-230vac-delayed-on-timer-relay-module-2-45-minute

    The only thing I'm unsure of now is the name of the latching relay - yes, I can find loads of them, but I think what we're looking for is something which mechanically locks-out/off, until reset.

    I get the concept, I just don't know what I'm looking for!

    Not sure I follow? Or I sort of do, but timeout relay resets when the power is cut.

    Exactly - it's a Stuart Float Switch - in fact, it's so old, it was actually made in England (how about that!).
    Found the manual - it can switch 3 amps inductive load, so I wonder why a relay was added?

    Yes, I thought of that - for example, running garden hose in the summer. Over-ride switch!

    No - it makes a horrible squealing noise, there's a burning smell and it cuts out!
    But don't forget, this project isn't just about stopping something filling when it's full, or even ensuring it overflows properly, but is also about mitigating for what happens when a pipe bursts or a tap is left on...
     
  16. bernardgreen

    bernardgreen

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    Easier and cheaper to replace a relay. Switch operates only the relay coil hence minimum contact wear in the switches so very long life time.

    Flow detector on the output. If it detects flow for an excessive length of time it shuts down the pump.
     
  17. EFLImpudence

    EFLImpudence

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    Of course.
     
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