I need some help with a time delay circuit. Please help

Discussion in 'The Projects Forum' started by arcaneiceman, May 14, 2011.

  1. arcaneiceman

    Thread Starter New Member

    May 14, 2011
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    Hello All.
    I have a project planned which basically needs to do the following and i dont really know where to start:
    I have a water well and a 1 hp motor that pulls water from it and almost finishes it in about 15 minutes and the well takes about 30 minutes to recharge after that, after which water can be drawn out again.
    I need to design a relay circuit or any other type of circuit that will allow the motor to be activated and keep it running for 15 minutes and then shut it off for 30 minutes and then turn in back on for 15 minutes and so on.. where do i start? please help. I am a beginner. thank you so much
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    I suggest that this would not be a good application for a timer. Although it may seem to you that the time required to fill/drain the well seems fairly constant, it will vary with how saturated the soil is, and how high the groundwater level is.

    What you really need is a float switch.
    When the well is nearly filled with water, the float rises up, causing a switch to turn on, energizing your motor.
    When the well is nearly drained of water, the float descends, causing the switch to turn off, thus removing power from your motor.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    Wookie, have you ever used a well like this? My folks were in an almost identical situation after my Dad retired from the Air Force. The well hole is deep (exact depth unknown, but guessing at 50'), and the hole is only 4"-6" or so wide. A float switch was not a practical solution for this problem.

    Part of the reason it is a problem is you have to prime the pump when the well has been sucked dry. I used to do it regularly, as did the rest of the family.

    How we handled it was manually timing it. We had a light rigged inside the house so we could see when the pump was on. When it was on for a duration we stopped using it for 30 or so minutes. It sucked, badly. I was a young teenager at the time, so there wasn't much I could do to help. It meant showers were a luxury we didn't always have. There is a small tank next to the pump with a float switch inside for setups like this, the pump fills the small tank, the small tank feeds the rest of the house.

    I've put thought into it long after I have left that aspect of country living behind. If I had to do it over I would have a mini water tower, and a timer similar to what the OP suggests. You could use a float switch to fill the water tower, which could provide a decent bath/shower and more, and add an industrial filter to clean up the water. I will never miss that sulfur taste again.

    To the OP, I'll help you as best I can. I need to know how much current your pump motor draws, and I am assuming a 120VAC system. You will need an outlet in the pump house (of course). What part of the world are you? City, State, Country please.

    You will need a 12VDC wall wart, the more current the better, lets say 2A for now. Email address via my profile if you can (click on my name). This site has a rule about private mails and 10 posts, you must have 10 posts or more to fully use all the features here, thanks to other people abusing the system.

    If you can email me using my profile we'll talk a little off line, but most of the technical stuff will be discussed on the forum. See the signature lines Wookie and I have posted. Don't post your email out for everyone else to see, this and other sites are regularly visited by bots harvesting address for spam.
     
    Last edited: May 14, 2011
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Bill,
    No, I haven't dealt with a deep well before. We did have well water when I was growing up in Michigan, but the well never ran dry that I remember. They finally ran city water out where we were living (rather rural area at the time) and my folks decided that was better than fooling around with pumps and water softeners.

    If the well were that deep and that narrow, it would need a long float stick indeed.

    Long-time family friends built a home on a hilltop south of Prescott, Arizona, and had to drill down several thousand feet before they hit water. :eek: They were lucky though; some friends of theirs drilled down 11,000 feet before they ran out of money - and still didn't hit water.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    OMG, that's incredible to a Midwesterner. I can pretty much stick my toe in the ground and find water around here! Those of us a stone's throw from the Great Lakes truly don't appreciate how rare that is on this planet.
     
  6. arcaneiceman

    Thread Starter New Member

    May 14, 2011
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    0
    well see the well im dealing with at the moment isnt all that deep.. its about 20 feet deep tho the radius of the hole is like 3 feet, so you can pretty much guess what sort of a hassel it is getting down there... float switch may work but id have to actually apply the float switch idea IN the well because there is only one operational pump... its a reciprocating pump by the way. so i could apply the float switch problem. Thought, i wanted to get around that problem by simply applying something that times the circuit allowing it to operate as long as i want. and then shut off for a variable duration. id really like to just keep it external. the power supply i have is 220-240 AC..
    i actually wonder if there is any such device or component like a timer that would do the trick. if not then float switch is my only other option.
    btw thank you so much for helping.
    and yes, i cant use many of the features of this forum yet.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    Wookie's float switch is the best solution, but you will need low voltage as an interface. It would self adjust, if you had lots of ground water then you could get more water faster.

    I'll pursue the timer option, if someone comes up with the float switch arrangement they can also post it, then you decide with one you need to use.

    The 30 minute off time is the important duration, the on time is critical, but the off time must be considered first.

    If your problem is like the one we were having while you are running water the pump is on. The need to fill pots and pans (or the bathtub) is the major problem, as it can run the pump/well dry. Sound about right?

    Just brainstorming (thinking out loud), something that integrated would be best for the on time. If you have 15 minutes of water, but 30 minutes of recharge, then if you were to run the water 5 minutes, sit for 5 minutes, and repeat this 5 times you would loose your prime. What you need is something that can "remember" how long it has been on over a duration, and trigger the hard off time when a thresh hold has been reached. In electronics this is called integration.
     
    Last edited: May 15, 2011
  8. Wendy

    Moderator

    Mar 24, 2008
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    Thinking about it I may change to a up/down counter for the timer. The down counter will count down half as fast as the up counter.

    Before I start drawing, how good are these times? 15 minutes on, 30 minutes off? This is important.

    This is definitely an application for a microcontroller if I've ever seen one.
     
  9. williamj

    Active Member

    Sep 3, 2009
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    arcaneiceman,

    I also belive that the use of limit switches is the way to go. With a timer circuit a water level sensor would still be needed to tell the pump that it is okay to cycle, running a dry pump is a VERY bad thing indeed.

    There is no need to actually go "into" the well to set up a limit switch assembly, simply hang it from the top and let geavity hold it in place for you. You will, of course, have to measure the difference between the high water level and the low in order to place your limit switches on the float switch assembly.

    The assembly itself could be constructed from easy to find pvc piping from your local home center and limit switches ordered online from your industrial supplier. I have attached a simple drawing to indicate one way of construction.

    The assembly mast would be pvc piping (length as needed) and the float shaft would be a smaller diameter pvc pipe (again length as needed) with a large toilet float ball epoxied and sealed to the bottom of the smaller diameter pvc pipe. The guides for the float shaft are nothing more than pvc couplings (of the apropriate size) with the internal lip ground out for easy sliding up and down the entire length of the float shaft. The couplings are attached to the lower portion of the mast and the limit switches attached to the mast above the couplings, appropriately spaced.

    The circuit itself is as simple as possible. Other than the two limit switches, one relay and one contactor would also be required, along with wire, tape and other miscellaneous supplies. A ladder diagram is also atteched to indicate current flow in the circuit, the actual wiring arrangement is up to you as required by your circumstance.

    All devices indicated in a ladder diagram are shown in a "deenergized state. So when power is applied any changes to relays and contacts have to be taken into consideration when following the circuit path.

    Current flow is as follows...

    Pump motor switches are put in the on position (I recommend ground fault circuit interupt breakers) and power is available to the pump motor and the control ciruit.

    The control circuit switch is placed in the on position (this "switch" could also be a contact from a seperate timer circuit). Current then flows to upper limit switch (ULS, shown normally open but will close when water is at the appropriate level), through relay coil (R 1) and through lower limit switch (LLS, lower limit switch is held close as long as water is above the lower level).

    When R 1 is energized all R 1 normally open contacts closed a current passes to coil R 1 keeping it energized until water passes the lower limit and LLS is release and LLS's contact held closed opens. Simultaneouslythe second set of R 1 contacts close passing current to the contactor coil (M) closing contacts M and energizing pump motor.

    When LLS is above water level LLS switch opensand current to R 1 coil stops, R 1 contacts open, pump motor stops and the whole circuit waits until ULS is closed when water level reaches high level and the cycle begins again.

    I hope this is of help and that I didn't miss or misrepresent anything. If I am wrong on anything please speak up (anybody).

    williamj
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    Just verifying, you aren't talking about putting a high voltage system down the well, right? This is why I mentioned he would need a low voltage interface, there is every indication it will get wet, and this is drinking water heavy in minerals, very conductive.
     
  11. williamj

    Active Member

    Sep 3, 2009
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    Bill,

    I'm not "advocating" high voltage and contact with water. As with any electrical usage, without having to be told, precautions must be taken.

    In the scenario above the limit switches can be be place above water level, above well top level or encased in waterproof containers. Or, as suggested by you, a low voltage control transformer and associated equipment can be aquired and utilized.

    One scenario not explored here is replacing the recipricating pump with a submersable pump. "High" voltage and water are mixed successfully all the time but it's done by professionals.

    I aplaud you concerns on safety and I say keep up the good work. I may not have stressed the safety factors but I think some assumptions must be made, such that the OP is able to determine whether or not he/she is capable of doing the work required or if they need to hire or consult the pros.

    again, keep up the good work,

    williamj
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    I understand, but when the voltage can come into intimate contact with flesh, safety first.

    I haven't forgotten about this thread, I have a design floating around in my head. The digital does seem to be the best solution, but it is definitely more complex.
     
  13. terra

    New Member

    May 12, 2011
    13
    0
    Good Day mates,

    Problem : Findout when to start and stop motor

    Option no1 : Timer as mention earlier(Timer driven)
    Option no 2; Float switch to control on/off (evnt Driven)
    Option3; Using Laser/infrared/RF to find out teh watre level and start and stop motor
     
  14. Wendy

    Moderator

    Mar 24, 2008
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    Option 1a (which is what is taking me so long) - a timer with an integrator, it measures the time on, if the duration exceeds 15 minutes (even with on and off water use) it shuts it down. Rather than shutting it down for 30 minutes, it lets the pump fill half way (15 minutes) then allows it to turn on again, for around 7 minutes.

    Both fill and pump cycles are integrated over time. With occasional heavy use you might no even know it is there, while a 30 minute shutdown will be painfully obvious.

    Current thought, an up/down counter, 8 bits

    The clock counts up when it is pumping. When the well is recharging the clock goes half as fast, and the counter is counting down.

    When all 8 bits are on it trips a specialty circuit, to shut it down until half way.

    The counter must stop when it is at 0 or 256.

    A simple relay will be used on wiring going to the motor. I am not comfortable with this, since the OP is not an electrician, but I don't see a way around it. A simple transformer around the motor/relay to detect when it is trying to turn on.
     
    Last edited: May 17, 2011
  15. arcaneiceman

    Thread Starter New Member

    May 14, 2011
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    0
    well that was exactly my point.. i would love to keep it external.. it would be just great for simply having a a circuit that simply allows or cuts power to the motor without me having to actually go down the well.. but if i AM going to put a float switch, i would simply attach it in the easiest way possible. thether it to the well pipe that takes the water up in the first place... i dont think it will be TOO much of an issue... but like i said, wont it be just better developing a simple timing circuit.
     
  16. arcaneiceman

    Thread Starter New Member

    May 14, 2011
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    and Bill,
    yeah the digital option sounds complicated by seems very effective... and you are right. and it would be perfect for the situation
     
  17. Wendy

    Moderator

    Mar 24, 2008
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    I've started sketching, when I have something substantial I'll put it up. Suggestion, spam this thread a little to get to 10 posts. I would like to talk to you off the record, but as long as your post count is under 10 it tain't possible.

    What part of the world are you. Trust me on this, it doesn't matter to me directly, I will help you in any case. It does help with things like shipping and parts however.
     
  18. arcaneiceman

    Thread Starter New Member

    May 14, 2011
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    dear bill
    thank you very much
    i live in karachi pakistan. im pretty sure i can get most of the parts, tho, i dont think they should be too much of a problem
    i appreciate the help a lot . thank you so much!
     
  19. Wendy

    Moderator

    Mar 24, 2008
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    Sorry I haven't checked back. Been thinking about it (the circuit), but haven't started serious drawing, just doodles. How much experience to you have with soldering circuits?

    I hope your area is calmer that others I've been hearing about. I have no problem with where you live, or you. The Irish, when they were having all the conflict, called it The Troubles.

    I'll see if I can't get it drawn up in the next week.
     
  20. magnet18

    Senior Member

    Dec 22, 2010
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    Same here...
    Ours is 100' or 300' or something but could be 10 feet with the same result.
    Heck, we have a marsh beside our house.
     
    Last edited: May 23, 2011
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