Float Switch question

off the gridoff the grid Registered Users Posts: 5
Hello Everyone,

This is my first post. Here's the scenario. I am pumping H20 approx. 3,000' with 350' lift. I have speced out a Grundfos 3SQF3 pump with four 205 Watt panels. I was planning to have a low level cut off float switch at the bottom tank and full cut off float switch at the top tank. Grundfos advises the max. run for their float switch is 1,600', which obviously comes up way short. Are there any other float switches, wireless set ups that will allow the top tank (supply) to communicate with the lower tank (spring). We were prepared to run conduit until we heard the bad news from Grundfos. Thanks a million.

Comments

  • icarusicarus Solar Expert Posts: 5,108 ✭✭✭✭
    Re: Float Switch question

    On quick glance,, look here. http://www.remotecontroltech.com/Applications/pumpcontrol.aspx

    I didn't read through very carefully, but it looks like this should be right up your alley. 3000 ft of wire must come at some cost, plus the installation, conduit etc.

    Tony
  • EcnerwalEcnerwal Solar Expert Posts: 101 ✭✭
    Re: Float Switch question

    Well, you might be able to use the water, and keep the wiring short.

    Given what lightning thinks of 3000 feet of wire, that might be a good thing.

    350 feet up is basically 150 PSI. If you use a finely adjustable pressure switch down by the pump rather than a float switch, and adjust it to cut off when the pressure is "to the top of the tank", you'd be good. You might not be as precise as a float switch, but you would not have 3000 feet of wire, either.

    If your upper tank can be configured to have a vertical pipe sticking up for the overflow that goes up a ways, the precision of the switch adjustment required to achieve a full tank would be reduced. The pressure would rise quickly as the overflow pipe filled. How that interacts with freezing is another problem, if you freeze.

    Another approach, if pipe is cheaper than wire, would be to run an overflow back down to the pump, and put the high-level switch in a "slowly leaking bucket" under the overflow.

    And a third approach (you have the low cutoff to prevent pumping the source dry) would be to have an intermittent water source that ran when the tank was full and the sun was shining. ie, just let it overflow (but do something with it - create an artificial wetland, or a rice paddy, or whatever...)
  • icarusicarus Solar Expert Posts: 5,108 ✭✭✭✭
    Re: Float Switch question

    And a third approach (you have the low cutoff to prevent pumping the source dry) would be to have an intermittent water source that ran when the tank was full and the sun was shining. ie, just let it overflow (but do something with it - create an artificial wetland, or a rice paddy, or whatever...)

    Or an overflow pipe that ran back to the well source with a water contact relay control. When the upper tank over flows, the water flows back to the source, triggering the shut off. Need 3000' extra feet of pipe however. I think the RF remote is cheaper though.

    Tony
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Float Switch question

    this makes me wonder why they limited it to 1600'? was it based on the resistance of the wire not carrying the current because if this is the case, larger wire can be used to carry it further. it would be more of an expense with larger wire, but the alternatives can also be expensive and any transmitter/receiver arrangement needs powered so problems can multiply. do they specify the gauge used for 1600'?
  • EcnerwalEcnerwal Solar Expert Posts: 101 ✭✭
    Re: Float Switch question

    If O.T.G. was willing to run conduit to put wire in, a less expensive hunk of water pipe (plastic, I assume) would provide the ability to have the float switch near the pump. If would also provide a spare pipe in place in the event of a problem with the main pipe (I like options for when things fail).

    Icarus's "water contact relay control" and my float switch in a leaky bucket serve the same purpose. The float switch is simpler, IMHO.

    You fill the upper tank. Water comes back down from the upper tank to the leaky bucket. The leak in the bucket is slow - a small hole. Water fills the bucket, the float switch turns off. The leak slowly drains the bucket - the float switch turns on. If the upper tank is still full, the bucket is filled again fairly soon and the float switches off. If the tank was drawn down, it takes longer, as the upper tank has to be refilled before it overflows down the pipe to the bucket again.

    I still prefer the pressure switch, for simplicity - but it may leave you with the tank not full when a float would have filled it (not a problem if you use the extended vertical overflow/vent - the limitation with pressure switches is the "deadband" which would amount to several feet of water on a switch that will handle 150 psi/350 feet of water.)
  • icarusicarus Solar Expert Posts: 5,108 ✭✭✭✭
    Re: Float Switch question

    The link I cited below:http://www.remotecontroltech.com/App...mpcontrol.aspx has a 1 watt transmitter that is all setup for solar applications, http://www.remotecontroltech.com/product/accessories.aspxvery specifically for the remote tank system that OTG describes. Sounds to me line it would be way cheaper than 3000' of either wire or pipe,,, or both.

    Tony

    I didn't bother to write to get a cost however
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Float Switch question

    tony,
    i have no doubt that would work and initially it may be cheaper, but imho the wire would be more reliable and cheaper in the long haul as batteries need replacing and those transmitters and receivers can fail. true, it is allot of cost in wire, but nothing will windup being cheap for this and it depends on what he wishes to do as he may go your route and just have a spare set of transmitters and receivers. the battery(if it has one as i didn't look, but assumed) can be a big problem though if it fails as one usually doesn't have one sitting around for years just in case.
    if they specify a certain gauge for that 1600' then he could figure going 3 more gauge numbers to halve the resistance and allowing 3200'. going 3 gauge numbers is odd and going 4 may be all that may be available to him.
    decisions decisions.:confused::cry:
  • icarusicarus Solar Expert Posts: 5,108 ✭✭✭✭
    Re: Float Switch question

    Let's assume for the sake of this argument that the spec number for the wire is say #18. Now if you go 3 sizes bigger that would put you into #12. 3000' of #12, plug either the ditching or the conduit has to come at some considerable cost. Understanding the cost and reliability of the transmitter system,, it still would be my choice...I think.

    Tony

    PS On the other hand, the OP hasn't shown back up so we may be arguing with ourselves!
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Float Switch question

    wrong as that would be #15 and is an odd gauge number as i stated so #14 could be used.
  • off the gridoff the grid Registered Users Posts: 5
    Re: Float Switch question

    Thank you guys for the insights. BTW, the medium range transmitter runs $2,300. I will be discussing these options with my friend who is installing the system. The pressure switch idea seems worth looking into, and is probably the least expensive option. I appreciate your input on this.
  • icarusicarus Solar Expert Posts: 5,108 ✭✭✭✭
    Re: Float Switch question

    $2300??? ouch! You would think some of the Ham whizzes here could cob something up cheaper. What was the cost of the shorter range version?

    Niel,

    Once again you reveal my ignorance. I have never seen wire in "odd" number gauges until #3. I didn't know there was even a #13 or 17 gauge wire. As I said in my signature,, I learn more every day,

    T
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Float Switch question

    don't worry about it tony as we all learn here. to be honest, i thought you misunderstood how i said it.
  • machinemanmachineman Solar Expert Posts: 129 ✭✭✭
    Re: Float Switch question

    Here's the reed float switch I used with the shut off lead on my linear current booster.
    http://www.gentechsensors.com/pdf/liquid/LS803-51p.pdf

    I used 400ft of direct burrial sprinkler wire which was the cheapest route. It comes in 500' rolls from Home Depot. Not sure about 3000' working. You could test it by hooking up 3000' while still in the rolls and see if it works before installing it? If not then return the wire if possible?

    Off Grid Cabin, 24V 440ah 6V GC battery bank, Xantrex MPPT60-150 CC, Magnum MS4024 inverter-charger, >1200w Solar bank

  • BB.BB. Super Moderators, Administrators Posts: 28,628 admin
    Re: Float Switch question

    You can also measure/calculate the resistance of a 500' spool--multiply by 6x.

    Get a small resistor from the local electronics store (I would probably double the value of the resistance for a minimum margin of error/safety factor). If it works, great--if not--some other solution.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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