Float Switch

DesertDweller
DesertDweller Registered Users Posts: 16 ✭✭
in Solar Water Pumping #1
I'm about to install my Grundfos CU-100 Float Switch into my cistern. Wondering what is the best way to "hang" this. From the top? Is there a gasket or strain relief connector for a water tight connection into the plastic cistern? Should I counterweight to keep the float from falling or by strapping the wire in place?

Help, I can't find pictures or tutorials anywhere about this!


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  • wellbuilt
    wellbuilt Solar Expert Posts: 763 ✭✭✭✭
    #2
     A float switch in a tank is a common thing , most of the time I just drop a pvc tube into the tank and let the end sit on the bottom . The top is secured and the float cord   gets zip tied to the pvc pipe with 16” of slack 
     I end up with 6 floats  hanging off the pipe some times
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  • wellbuilt
    wellbuilt Solar Expert Posts: 763 ✭✭✭✭
    #3

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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #4
    Hanging from the top is the easiest, drill a hole slightly larger than the cable and tie a knot in the desired position to act as a strain relief, since it's at the top it doesn't have to be water tight 

    The need for a counterweight, or not, depends upon the control desired, so it's a difficult question to answer definitively without details on what it is you are trying to achieve. One needs to think very carefully when designing automation in offgrid applications because there are times when pumping water is undesirable, such as at night or when PV availability is low.

    Designing an automated system that takes everything into consideration is possible using the right components, wether it be computer based or electromechanical, both  would still rely on basic sensors to provide information and a single float sensor provides limited information.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
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  • wellbuilt
    wellbuilt Solar Expert Posts: 763 ✭✭✭✭
    #5
    Most of the floats I use have to flip all the way up before it triggers a response . 
     Hooking the float to the pipe allows you to lift the pipe out to adjust the height or change the switch with out reaching into the tank . I do sewage pump all the time . 
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #6
    Make sure there is room for the floats to move/up down... Had a small sump area and "just enough" room for the float switch to move--Until it did not, and flooded out my furnace. Replace with captive redundant floats and an alarm.

    Redundancy/cost of failure is always a question... For example, if the float does not turn off the water--What happens if the pump runs for 24 hours when you are not home... Take your battery bank "dead"? Water overfill cause erosion of ground support, flooding of basement, etc.? Second float for redundancy? Alarm "float", wet floor alarm?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • DesertDweller
    DesertDweller Registered Users Posts: 16 ✭✭
    #7
    hmm...now I'm thinking overflow in case the float switch ever fails! I suppose I can put in another bulkhead at the top and run a pipe.

    What about venting? Is this neccesary for a buried cistern?

    I still want to find some nifty strain relief connector for the float switch but I might just run it through a conduit connector and silicone the gaps. I really don't want dirt to get in there!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #8
    From a mechanical point of view--You need to vent tanks to prevent negative pressure (drawing water out of tank) from collapsing the tank. And filling of water to prevent blowing up like a balloon.

    You want a screen to keep out insects, squirrels, rats, etc... And don't want dirt/ground water contaminating your water.

    Your venting may need to be better than PVC if you have bears in the area (especially kitchen and other vents that may have smell of food or water in dry season.

    I don' know about venting (or not) to keep water "fresh".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • wellbuilt
    wellbuilt Solar Expert Posts: 763 ✭✭✭✭
    #9
    O it’s a under ground tank , is it plastic or Concreet ? 
     You need a good size vent 11/2 so it won’t get plugged up  .  
     Don’t use Regular silicone to seal up a tank for drinking water . 
     Most plastic tank lids have a built in vent but can suck dirt in . 
     If you add a bull head fitting at the top , get the type that are threaded on the inside allso . 
     Use threaded pvc fitting inside and out  ,extend  the pipe into the tank 12” below your hi water mark . 
     the vent needs to be 24” above the ground 
     thread your fitting into the tank and glue a 11/2
     sink trap  elbow on top so the hole faces down they sell screens that snap in . 
     Your float wire can just be drilled into the side of the vent just below ground and wrapped up with pump  tape to seal it . 
     On the bottom drill a hole 1” up from the end of the pipe , run your wire thru the hole and 
    zip tie it with about 12” of slack . 
      I find floats in tanks just floating around louse all the time . Do your self a favor and use pump tape And zip ties for your float 👍
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  • DesertDweller
    DesertDweller Registered Users Posts: 16 ✭✭
    #10
    I like this plan. But what do you mean by "pump tape"?

    What about drilling the hole for the float switch wire ABOVE ground so no dirt gets in? I have a PVC electrical connector that I might be able to attach to the vent pipe and run the wire through that.

    HydroMaxx 100-Pack 38 in Dia Liquid Tight Non Metallic Electrical PVC Conduit 90-Degree Angle Fitting Connector-CAF038100 - The Home Depot  

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  • wellbuilt
    wellbuilt Solar Expert Posts: 763 ✭✭✭✭
    #11
    You need the tank to vent , that fitting is conduit I run my float cable thru the pvc vent .
      Pump tape is green or gray and is used for potable water a lot of guys use electrical tape but it’s plastic , pump tape is more like rubber .
     Put the wire thru a snug hole bend the wire up and zip tie it , then wrap it with the tape you will ever have a problem . 
     I run 4/5 float on one pole . Plumbing supply has the tape 
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  • wellbuilt
    wellbuilt Solar Expert Posts: 763 ✭✭✭✭
    #12

    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
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  • DesertDweller
    DesertDweller Registered Users Posts: 16 ✭✭
    #13
    OK sounds good. When you mentioned running the vent pipe 12" below the high water line, do you mean, the pipe inside the tank needs to be submersed in water?
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  • wellbuilt
    wellbuilt Solar Expert Posts: 763 ✭✭✭✭
    #14
    Yes , the float wire will go thru a small hole  , then zip tied and taped at the bottom of the pipe . 
      You need 12” of wire on the float so it stands  up straight to turn the water off . 
      You could add a tee above the water line so the tank vents  or I’ve drilled  3 1/2 “ holes on top 
     so the tank draws air there .
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
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  • DesertDweller
    DesertDweller Registered Users Posts: 16 ✭✭
    #15


    Cable Glands! I found out what they are called. They make a waterproof seal around the cable as you tighten the nut. I can use these to bring my solar wires into the house as well. Hopefully these can replace the need to zip tie and tape! 
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  • wellbuilt
    wellbuilt Solar Expert Posts: 763 ✭✭✭✭
    #16
    Nope the wire will crack at the compressing point , it happens all the time . 🤗
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
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