Relay/timer design help

Discussion in 'General Electronics Chat' started by gturnbull, Jun 1, 2009.

  1. gturnbull

    Thread Starter Active Member

    Jun 19, 2008
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    Hi Folks,

    I am trying to design a circuit and I am not sure on the components needed.

    I know what I want it to do and I know it's possible, but just can't figure out what I need.

    What I want to do is as follows,

    Float drops calling for water, operates relay, activates pump drawing water from another tank, tank gets filled to required level, float switch rises opening relay, this is simple enough, but I also want to incorporate a timer, so when the relay operates the timer counts down and should the water in the tank run out it shall only operate for 15 seconds maximum, it cannot be latched on for 15 seconds the timer is only there for backup/safety.

    The system shall be run in 12v DC.

    There shall be a power on light and a pump on light.

    What parts would I need for this, I want it as simple as possible.


    Thanks in advance :D
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    I've done the same funtion differently. I used optical liquid sensors, they are a self contained three lead parts (+12,gnd,sense) that use an LED bouncing off a surface to detect whether the device is immersed or not. I put one high, one low, and a timer relay.

    Only mention this to possibly give you more ideas.
     
  3. gturnbull

    Thread Starter Active Member

    Jun 19, 2008
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    0
    Hi Bill,

    Thanks for the reply, I too looked at optical sensors, but they are a bit more expensive.

    I am trying to do away with the need for the high sensor/float, as having the in built timer should the sensor/float malfunction it will only operate for the say 10/15 seconds I have on the timer, this shall not reset until the sensor/float de-activates.

    The system shall be run by the sensor/float, the timer is safety only.

    I think its a logic timer I need I/O, timer starts (I signal) and only resets after a "O" signal is sent and will not ativate till a "I" signal is sent and so on.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    I bought an off the shelf timer, with a knob on the top to set the delay. Might also be a bit expensive though.

    I don't know your level of electronics, have you seen this...

    555 Monostable

    You may want to put a transistor in front, I'll draw it and be right back...

    [​IMG]

    There are lots of other ways of doing this, the positive edge transistion needed an inverter, provided by the transistor.
     
    Last edited: Jun 1, 2009
  5. gturnbull

    Thread Starter Active Member

    Jun 19, 2008
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    If I am being honest, and I am, It's all greek to me.

    It's just a little project I am working on, I know alot about domestic electrics, but all electronics is a whole different ball game to me.

    Can you suggest any good articles to help me, I have the basic understanding, but not what all the bits do, I know what I want to do, just not how to go about it.

    Thanks
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Did you read that article I suggested? I have several I've written for beginners. Here is my blog for even more choices...

    Bill's Index

    That industrial relay timer I suggested is pretty easy to use. They very somewhat in price, and basically have the circuit I drew already inside. This means you don't have to solder something together, or make a box (though the larger project will need one). Think Grainger, or McMaster Carr, both have online catalogs.

    Whatever you decide, we'll try to help out. I surprised one of the other guys haven't jumped in already, usually the hard part is filtering through all the ideas. :D

    Just curious, (and it just occurred to me), do you need someone to help diagram the whole system?
     
  7. gturnbull

    Thread Starter Active Member

    Jun 19, 2008
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    Hi Bill,

    No I never read that article, never noticed it was a link to an article to be honest, I will have a read tonight.

    I have got a programme called "Tina" to help design and test the circuit, I had a look at it last night and think it will take some getting to grips with.

    I don't want someone to do it for me, but if someone is willing to draw a diagram, I would be very grateful.
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    Have you got a float switch picked out yet?
     
  9. gturnbull

    Thread Starter Active Member

    Jun 19, 2008
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  10. Wendy

    Moderator

    Mar 24, 2008
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    Cool. It would have been a drop in replacement for my sensors, almost. You are wanting to use two of these, one for top and one for bottom. Correct?

    Is the pump motor 120VAC?

    Give me a day or so and I'll try to reconstruct what I did. I'll probably refer you to the time delay relay, but if you want to try to build the 555 circuit that is cool too.

    By way of information, my project was for a sump tank off a chemical effluent. We feed the output of the pump through a fancy filter and then to city water drain.
     
  11. gturnbull

    Thread Starter Active Member

    Jun 19, 2008
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    Thanks for all your help Bill.

    I really only want to use 1 float, but have a timer there should the float switch go faulty, the unit shall only run for 15 seconds tops, but in normal working conditions the level shall be controlled by the float.

    If the circuit could be designed with a 2nd float opton (high level) just in case I go for that design.

    It would have an on/off switch, red power on light and a green pump on light

    The system is run on 12v dc.
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    I'm going to bed for the day, but a 2 float system (as cheap as they are I'd think about a 3rd for safety) is much simplier. 2 Switches, one relay. BTW, does the pump motor use 120VAC. I asked before, but didn't see the answer.
     
  13. gturnbull

    Thread Starter Active Member

    Jun 19, 2008
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    The system runs on 12v DC, This includes the pump.

    I am running a 3 float system at present just wired through a relay.

    Just trying to do away with the need for the other 2 floats by replacing them with a timer, so the system should not keep running if the float switch fails, but the float will govern the system in it's normal running condition, the timer is only there for backup.
     
  14. gturnbull

    Thread Starter Active Member

    Jun 19, 2008
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    To clarify,

    I want a timer to start counting down when a float switch "makes" and then stop when the float switch "breaks", should the float switch not "break", the timer shall "break" the circuit when the set time period is up and will not reset until a "break" signal is received.
     
  15. Wendy

    Moderator

    Mar 24, 2008
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    Basically what I described. 3rd time is a charm, what is the motor your running, 120VAC, or a DC motor?
     
  16. gturnbull

    Thread Starter Active Member

    Jun 19, 2008
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    4th time :D

    The whole system is 12v DC including the pump :)
     
  17. Wendy

    Moderator

    Mar 24, 2008
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    OK, gotcha, it's either going to be pretty low volume, or pretty high current.

    I do like those float switchs.
     
  18. gturnbull

    Thread Starter Active Member

    Jun 19, 2008
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    Low volume is probably exactly what I am looking for, the application I am using it for is to top up evaporated water from a marine fish tank.

    I was going to use a 12v adaptor like this CLICK ME It is 2amp or 2000ma 24w

    The pump shall be 15w with a power on light and a pump "pumping" light also an on/off toggle switch.

    A link to the thread, of the auto top up unit I built, I have it on the Marine keepers forum I use alot. CLICK ME

    Thanks
     
  19. gturnbull

    Thread Starter Active Member

    Jun 19, 2008
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    Bill,

    Just to complicate things, or maybe not. :)

    Would it be possible to allow for a small buzzer/sounder, should the timer reach the end on the timed cycle before the float switch sends the "break" signal, but reset when the "break" signal is received. (only sound if the system is in fault status.

    If it is to complicated, don't bother, it's just yet another safety feature I was thinking about.
     
  20. Wendy

    Moderator

    Mar 24, 2008
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    OK, I think this will do what you want. If the top switch is not de-energized the pump will not turn off.

    [​IMG]

    Or not, Let me reread your posts to see what else. This will run the pump an minimum of the timer, but will cut off after the timer times and AND the low float switch opens (no liquid).
     
    Last edited: Jun 3, 2009
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