Relay design help

Discussion in 'Electronics & Electrics' started by oped, Oct 18, 2018.

  1. oped

    oped Member

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    Hi everyone, I have a relay design problem which seems to have stumped the Jaycar people so i thought I would turn the the smartest community I know, OCAU!!!

    So I have a tank of water at waist height (on a table) which is connected to a tank sitting on the floor via PVC piping which has a gate valve halfway to control flow, to an extent.
    This constantly feeds into a bottom tank, which also has a tap at the bottom which goes to a water pump which pumps the water back to the top tank... which then flows back down to the bottom via PVC then up again.

    Now foolishly at the start I thought I could 'match' the water pumps flow using a gate valve on the PVC piping with some trial and error.... I could, but as soon as some water evaporates it'll be out, flooding or over draining the bottom tank.

    Sooo, I thought my solution was to buy a float switch, install it in the bottom tank to turn the water pump on once it hits over its desired water level, so that the pump and switch is de-activated until the water hits the float switch level and it would turn the pump on to keep it from overflowing.
    I went to Jaycar and one of the guys there designed me a relay because he advised me my plan to splice the float switch into the active or ground (to cut the power to the pump) was apparently a bad idea lol. There's a diagram of the relay below.

    Float Switch Relay.jpg

    It works, but it reaches a balance where the pump gets turned on for a second, then off for a second, then on for a second, off for a second etc etc. and it sounds like that pump will be fucked in no time or will drive me insane first.
    Sooo my second idea to that would be to add some part to the relay so that once the float switch turns the pump on, the pump stays on for a designated amount of time like 30 seconds or a minute, so it will drain more water than needed before it stops, giving the pump a rest while it refills.

    So I went back to Jaycar to find if there's a device to do so, I was told there is no easy or direct way to do so and they were kinda stumped how to do it at all, so he had me buy some arduino/raspberry pie type stuff and said to google how to use it and add that to the relay....
    Seems a bit complicated and it seemed like he just wanted me out of his face at that point lol so I'm guessing it's not the best solution.

    Does anyone have any ideas to my problem?
     
  2. _zak

    _zak Member

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    A 555 IC would be the ideal way to do this. You can set it up to output a pulse for a fixed period of time based on an input (the switch closing). The only issues to overcome would be supplying low-voltage DC and ensuring the coil of your relay is suitable.
     
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  3. RussellK

    RussellK Member

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  4. OP
    OP
    oped

    oped Member

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    Thankyou both so much that's exactly what I was hoping to find!!!

    I can't wait to tell Jaycar about the 555 IC when I return the other crap they sold me, thanks zak,
    And thankyou Russel I wish I bought that at the start, that is perfect!
    Do you know, do I just replace my current float switch with this one in the relay I already have built?
     
  5. paulvk

    paulvk Member

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    Get a second float switch that is lower than the first
    The higher one turns it on , the lower one turns it off
    And I would not have mains power on the float switches as per your diagram its just too dangerous
    so a small transformer is needed a 12v DC plug pack would be good
    I will get a diagram together for you as soon as I can
     
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  6. OP
    OP
    oped

    oped Member

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    Thank you so much Paul! I was thinking that after I noticed when you look at 2 stage/dual float switches they have 4 cables coming out which suggests two different switches.

    Is there a way to add it into the relay I've already built? The relay cost me $100 in parts as it's quite big and in a waterproof relay box, all cables pass through the box with waterproof grommets
     
  7. paulvk

    paulvk Member

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    Have you any plug packs laying around from cordless phone, xmas lights or similar
    and how good are your construction skills some simple soldering?
     
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  8. OP
    OP
    oped

    oped Member

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    I do, I have plenty of those packs lying

    I'm good with constructing stuff, especially soldering. I'm a goldsmith so soldering is my jam but yeh, soldering electrical stuff I can do. I can read simple electrical diagrams, high school level, but I never learnt relays or anything beyond a switch haha
     
  9. paulvk

    paulvk Member

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    Have you a 12v DC one it will should be on the pack it does not need to be very big as its only
    going to run a small relay which in turn will drive the relay you already have
    So you will only need another small relay and a float switch
    what will happen is the top float will operate the relay
    the relay will keep itself operated through two of its contacts and via the second lower float
    when the water gets below the lower float this will release the relay
    then the tank fills ,the lower float switches on but relay does not operate,
    water gets to top float it operates relay, pump on
    this repeats itself.
    Note now all the 240V AC will be inside the box !

    the relay Jaycar SY4065 + float switch so $27.90
     
    Last edited: Oct 20, 2018
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  10. dakiller

    dakiller (Oscillating & Impeding)

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    RussellK's linked float switch will work without a relay, plug pack or anything else. Just wire the switch inline with the pump and that is it. Does not get any simpler.
     
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  11. OP
    OP
    oped

    oped Member

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    Thank you so much PaulVK, I am going to attempt to build it today, I just watched some videos about how relays work. I'll have a go at it and let you know how go.

    The only single problem is it's method of reading the water level doesn't suit my tank. My tank is quite narrow so there is no room for the float to float out to :(
     
  12. paulvk

    paulvk Member

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    Yes the float is simpler but adjustment between on off is unknown
    Ok have drawn a diagram.
     

    Attached Files:

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  13. OP
    OP
    oped

    oped Member

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    PaulVK, thankyou so much for this diagram. I must admit I bought all the parts straight away and have been trying to wrap my mind around the diagram (with my little knowledge) but had to pause due to work, anyway I'm back on it again and I think I understand it, but I wouldn't mind you/someone with more knowledge to check over it for me just to check I got the normally open and normally closed bits correct.
    I've just re drawn your diagram in a way I understand.
    At the bottom is the old relay and the new parts (the relay itself burnt out from on/off'ing constantly which is why I have another now)
    [​IMG]
    [​IMG]
     
  14. paulvk

    paulvk Member

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    Yep you have it

    When the water rises above the top switch it operates relay this locks up via its own contact
    While the bottom float switch is operated the 12v relay can work so when it goes below this relay releases pump stops
    12V only on float switches so if a leak occurs you do not get fried!
    Note that pump relay is 240V ac not 24V that was so you could use your existing relay
     
    Last edited: Dec 11, 2018
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  15. MUTMAN

    MUTMAN Member

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    i propose no relays and no float switch ...
    have a look at aquariums with sumps. you setup the top tank to have a 'overflow' to the bottom. the pump lives in the sump and runs continuously.
    the overflow only flows when the pump has pushed enough water back up.
    the system reaches equilibrium almost instantly. if the power goes out no loss, no crazy restart procedure
    sump needs enough capacity to hold the drain back water from the plumbing and the 'head' in the top tank

    https://www.google.com/search?q=aquarium+overflow+sump
     
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  16. OP
    OP
    oped

    oped Member

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    Dude, that's a brilliant idea! BUT, what would be the sump tank is actually the elevated tank, and the tank which is lower in elevation is the one which the water level is important. Sorry should have mentioned that, unless you could for see a way of employing it to the reverse.
    I wish they made the a float switch like the cheap jaycar ones which were 240v
     
  17. OP
    OP
    oped

    oped Member

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    Awesome, thanks man, haha you've helped me learn relays and wiring diagrams, thanks again.

    haha yeh I almost bought a 24V bilge pump which handles 30amp, lucky I brought the old relay and the jaycar dude looked at what I brought in rather than what i told him hahaha
     
  18. MUTMAN

    MUTMAN Member

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    add a third tank the one you want with a constant level is the middle one ???
    this time the top and middle tanks have overflows, the bottom is still the sump
    in use the sump doesnt need to be 'lower' than the tank, it could be behind the show tank just a slightly lower edge height compared to the show tank
    hang on edge overflow that self start are easy enough to build and take up little room. stand pipes are noisey (sound like a toilet thats running constantly) and use a bit more room inside the tank
    anyway, food for thought, and you've already bought the gear, so on with the show :)

    this seems like a good candidate for an arduino, a ultrasonic level detector, and a PID library running a small varible speed dc pump ???
     
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  19. OP
    OP
    oped

    oped Member

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    PaulVK you are a genius, it works absolutely perfectly!! Thankyou so much mate, this also taught me how to draw and read wiring diagrams and how relays work
     
  20. OP
    OP
    oped

    oped Member

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    I will be making another similar system which I plan to be simpler and cheaper on equipment so this sounds like the go. Especially when the first relay burnt out and I came to find the bottom tank completely overflowed and the top tank empty haha Also super keen to learn arduino programming. I have a jewellery store and will be building a breach room entry type deal with magnetic locks which only open once another door has closed and locked. Not to mention the fume cabinet and room ventilation I plan to install
     

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