Total Newb Graciously Asking For Help

Discussion in 'The Projects Forum' started by T Chaffin, Jun 9, 2014.

  1. T Chaffin

    Thread Starter New Member

    Jun 9, 2014
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    My name is Taj. I have zero electronics experience. I am hoping a generous soul will help me with what appears to be a simple application.

    We have a 40 thousand gallon reservoir underground, at the top of our 70 acre property. We would like to be able to get a sense of how much water is in the tank without walking up there and looking inside. I have looked at many applications and the one I am hoping to employ appears to be the simplest. "which is all we really need".

    I want to connect three of these mercury activated float switches http://tgwastewater.com/sje-rhombus-sensor-float-mini-sump-pump-switch-submersible to a pvc pipe and submerge them inside the reservoir. When the reservoir is full, all three mercury float switches would power three individual led lights pieces. As the level goes down the switches would fall and go the "open" position in order, thus turning off one, two or all three lights depending on how many switches drop because of the water level. This would allow us to determine if the tank is mostly full, half full or almost empty.

    Here is where I need help. I have no idea how I would wire such a thing.

    Can someone please tell me like I am a 10 year old, how to tie in the floats to the transformer to the lights? Like, I cannot visualize how I would do that. Thanks so much in advance.
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Note on the data sheet that this switch is not the best for very low current loads, like LEDs. Is this for a remote indicator, or do you want the lights where the tank is? Also, is AC power available up there? It might be simplest to use normal AC light bulbs, and that's the kind of load the switch is designed for.

    ak
     
  3. Brownout

    Well-Known Member

    Jan 10, 2012
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    You might want to call the toll-free number and ask them why the switch isn't recommended for low amperage switching. It might be that you'd simply be paying for extra safety for applications that are already 'intrinsically safe.' If that's the case, it should be nobody's concern but your own.

    Lighting a LED with these switches is as simple as connecting one wire to a DC voltage, say 6V, and the other wire to the LED in series with a current limiting resistor. If, for example, your led wants 20mA and runs at 2V, the resistor would be calculated as:

    R = (6-2)V/.02A = 200ohms. So, a standard 220ohm resistor would be appropriate. The wattage rating of the resistor would be W = V*A = 4*.02 = 80mW (.08W) And so you need a standard 220ohm, 1/8watt resistor.

    Of course, you'll use different values for your operating voltage, your LED voltage and LED current. So, the general form of the above equations are:

    R(ohms) = (v(operating) - v(LED))/I(LED)

    R(watts) = (V(operating) - v(LED) * I(LED)
     
  4. inwo

    Well-Known Member

    Nov 7, 2013
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    It looks like your electrical method will get answered.

    Some other thoughts:
    The pressure, when measured at a fixed point will correspond to water level.

    In other words a pressure gauge anywhere in the line below tank will show feet of head.

    Of course it requires a separate sensing line if you have flow.
     
    Brownout likes this.
  5. wmodavis

    Well-Known Member

    Oct 23, 2010
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    It will work fine if you use a high current CREE LEDs which have various specified currents depending on the one you pick but well above the 30mA minimum the float switch requires.

    Each float switch could be wired in series with an appropriate source of power to the LED you want to turn on.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    Why would flow make a significant difference? :confused:
     
  7. wayneh

    Expert

    Sep 9, 2010
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    He was referring to a pressure gauge on the line, potentially not near the tank itself. Dynamic pressure drop across the line would make it difficult to estimate static head.

    My solution would be a vertical piece of clear plastic hose connected to the reservoir at its (the hose's) bottom and vented at the top, suspended vertically outside the tank. A "sight glass". Tried and true, no power, almost no maintenance.
     
    inwo likes this.
  8. Brownout

    Well-Known Member

    Jan 10, 2012
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    That won't work because the tank is under ground.
     
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Because the contacts are cadmium silver or some other alloy that relies on arcing to keep them clean. Silver makes for small contact area with excellent conductivity, but it oxidizes. An intentional arc burns away the oxide. This is common in appliance switches. For low currents the contacts should be gold plated so they stay clean without intentional burning.

    ak
     
  10. Brownout

    Well-Known Member

    Jan 10, 2012
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    A brief over current is easily created with a simple RC network, if using DC.
     
  11. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Some questions:

    Where and what powers the lights?

    What lights?

    Are the lights at the tank or somewhere else?


    Here's one way to wire things:

    [​IMG]

    Note in a schematic the connections are important, the physical arrangement is not a factor. Let me know if you need a version showing how the wires would run to real world parts.
     
  12. wayneh

    Expert

    Sep 9, 2010
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    Haha, a forehead slap for me.

    The "sight glass" approach would still work - same as a pressure gauge - if it was downhill far enough.

    Another electronic approach would be an ultrasonic sensor at the top looking down at the surface of the water.

    I'm pressing the case for non-contact methods.
     
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