looking for a latching relay

Discussion in 'The Workshop' started by aidank, Feb 8, 2020.

  1. aidank

    aidank Well-Known Member

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    Im looking for a relay for a project. The relay will be connected to a 2 position water tank level sensor,

    I want the relay to have two inputs such that when the high level sensor pulses and is triggered in the water tank the solenoid valve connected to the output of the relay turns on and stays on until the low level sensor is pulsed in the water tank and triggered.
     
  2. whichwire

    whichwire Well-Known Member

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    could you used a fairly standard relay. When the high level switch closes, it latches the relay. Have the low lever switch in that circuit so that when it opened the feed to the relay is cut, unlatching the relay?
     
  3. Knickam

    Knickam Well-Known Member

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    You will only need a single 2 pole relay to do this.
    The attached drawing should help.
    The low switch needs to be on an open contact when the level is low
    Level rises, Makes low switch and allows power onto high switch/relay contact
    High switch makes when level reaches high switch
    This energises relay, 1st contact latches relay and second contact energises solenoid
    Level starts to drop and high level switch opens
    Relay states latched due to 1st contact
    When level reaches low switch, Switch opens removing power from relay opening both contacts and de-energising solenoid
     

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  4. Bluffegan

    Bluffegan Active Member

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    You could also buy an off the shelf float switch may be worth considering.
     
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  5. aidank

    aidank Well-Known Member

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    After some thought I found out I will be using a 1.5" valve on a suction line, thus a solenoid valve is not suitable, when solenoid valves get up that big they become pilot operated and are therefore not suitable for sction lines.
    Therefore I will be using a 2wire motorized ball valve with a 7 second open close time which will do me nicely.
    This motorized ball valve has limit switches so it wont sit there humming away in either fully open or closed position.

    It is a 2 wire ball valve and operates as follows when the black wire is - and red is +, valve closes, when the + and - are reversed the valve opens.

    So project description is now as follows
    Low level sensor in the tank is triggered the ball valve closes. The water tank then fills up with water. The high level sensor then pulses and the solenoid valve opens. It then needs to remain opened until the low level sensor is triggered.

    I need a DPDT relay to do the forward reverse control of the motor circuit. How do I connect my sensors, as these will be just 0.1sec pulses rather than continuous input
     
  6. scoffcruddle

    scoffcruddle Well-Known Member

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    Make sure you ball valve is the highest grade of stainless,Chlorine eats anything copper,most balls are made of copper.

    I bought a relay to do what you want a couple of years ago,I’ll look later to find the exact one.
     
  7. aidank

    aidank Well-Known Member

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    for exactly the reason you mention I was going to go with UPVC, this is what i had in mind

    and here we go a breakdown of the materials http://www.china-tonhe.com/?u=2&m=product&id=571
     
  8. scoffcruddle

    scoffcruddle Well-Known Member

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    I don’t think it will cope with the temp of the water,only rated to 55degrees c.

    I’ve a couple of these https://www.i-acs.co.uk/store/index...rQZEpB2ZW4SNOjDYyaA8gP0MFrHjcQMIaAtIwEALw_wcB
    Bought off eBay for £26each you can use them on a stainless valve.

    Personally I’d favour a pinch valve on the suction tube,this would mean no contact with chemicals or hot water.
     
  9. aidank

    aidank Well-Known Member

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    what do you use those actuators for if u dont mind me asking.
     
  10. scoffcruddle

    scoffcruddle Well-Known Member

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    I bought them to turn water on and off remotely using an app.

    They are great because they can use ac or dc power.
     
  11. aidank

    aidank Well-Known Member

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    how long to turn through 90degrees, from the document it says less than 75seconds motor running time. Its hardly that long is it ?
     
  12. scoffcruddle

    scoffcruddle Well-Known Member

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    It didn’t seem long,I’ve another the same as the plastic one you showed but that is far slower.
     
  13. Bluffegan

    Bluffegan Active Member

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    Can you outline the process which the controls are required for. Is it the batch mix of a product or the prevention of a tank over filling.
     
  14. aidank

    aidank Well-Known Member

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    @Bluffegan

    I want to improve the hot wash on the milking machine via shutting off the suction pipe and allowing a quantity of water to build up in the wash trough before the suction restarts.

    I propose to do this via installing a motorized valve on the suction pipe to shut it off until approx 40l of water has returned to the wash trough. (There would be approx 100l of water in the entire milking machine.)
    Shutting off the suction will allow the level of water in the wash trough to build up. When the valve opens I will get a powerful flow of water through the plant thereby giving me a much better wash. Shutting off the valve will also keep the suction system from pulling in cold air and keep the wash much hotter.

    I propose to use a low level and high level sensor in the wash trough and a 3PDT relay to control the valve as per wiring schematic attached.

    My relay should operate as follows as per the electrical drawing.
    • When low level and high level switch are made the coil in the relay pulls in and switches the 3 Poles. The valve opens and water sucks up and begins to drop. Pole one is wired across the high level switch thus as the water drops the valve remains open.
    • When the water drops below the low level the entire circuit switches off and the poles flip back to home position and close the valve.
    The cycle then repeats until Auto/Manual Open switch is pressed which keeps the valve always open.

    I guess I will need a second switch for power for the entire thing rather than keeping power alwyas on the relay.

    and here we go a 3PDT with a 24v coil https://ie.rs-online.com/web/p/non-latching-relays/0536912/

    All of my porposed wiring is an extension of what @Knickam and @whichwire proposed above
     

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    Last edited: Mar 30, 2020 at 9:00 PM

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