Connect with us

water level high point, 12V relay kick on help

Discussion in 'General Electronics Discussion' started by DIYer, Jun 13, 2012.

Scroll to continue with content
  1. DIYer

    DIYer

    12
    0
    Apr 30, 2012
    Ok,.. so i have a 12v solenoid valve, hooked to a 12V/30A Relay, which is powered by a 12v car battery. Only part i'm stuck on, is how to pop the relay when water level reaches a high point in a container. WITHOUT using a float! Mechanical devices fail. The valve is an N/O solenoid, and its a last defense in case of flood, so although it'll often never be used, it needs to work like a charm when asked. I've tried a few things i thought would work, but i know little about electronics. I thought wiring the solenoid directly to the battery, then run the negative wire through the water container, so if water got too high it would bridge the connection, pop the relay, and the N/O valve, but it doesn't seem like theres enough conductivity across the water because it won't reliably pop either the relay or the solenoid. I have one of these liquid level controllers that would work, but its a spare and i don't want to have to use it just for this failsafe measure. Anyone know a cheap reliable way to pop my 12v N/O noid incase of overfill?
     
    Last edited: Jun 13, 2012
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,164
    2,550
    Nov 17, 2011
    My coffee machine uses this technique:

    Within the tank there is a tube containing a small magnet within a shell such that the magnet floats on water. this tube is placed directly at the side of the tank (in fact, it is part of the tank). The magnet rises and falls with the water level.
    Outside of the tank is a sensor which is activated if the water (and thus the magnet) reaches a certain level. I don't know what's in my coffee machine, but a magnetically activated reed relay could work. My coffee machine has been doing fine for years now.

    I know this is kind of a float but it seems to be a reliable one. Plus it doesn't take up lots of space.

    If you really can't afford even such a simple mechanism, there are several other ideas. To list but a few ones:
    1) put the tank on a "scale", a mechanism that trips if the weight of the tank reaches a certain level.
    2) use an ultrasound detector to measure the water level
    3) use an LED and a phototransistor. As long as the LED is outside the water, its light will be reflected back to the phototransistor. If the water reaches the LED, the light will be diffracted within the water, so less light will reach the phototransistor.


    Harald
     
  3. DIYer

    DIYer

    12
    0
    Apr 30, 2012
    Thats some good outside the box thinking Kapp. Thanks for the reply. The right float might work, but i've yet to see one for sale i like. See i fill the container pretty full, and the Liquid Level Controller stops the fill process close to the top, so not sure i have room for a float. It would have to click on reliably within 1" too high liquid level, more then 1.5" too high and liquid will overflow onto the floor. I think this excludes a scale too, as the weight to trip the valve on would be a small window to hit, also would cost more then the spare LLC i could use to accomplish this ($40).

    Wires in the water (just like how the LLC works) seems like it would be the most accurate solution, but i'm not sure how to trip the 12v relay that way. 3.8v is suppose to kick it on. In my testing, putting 12v into the water sometimes kicks on the LLC, and wont let it shut off, so that's a problem too.

    The whole reason i want this failsafe shutoff valve in place is because one day the LLC realized it was time to refill, but didn't stop filling! Thankfully i was home and noticed before too much liquid hit the floor. There is relatively nasty liquid in this container too, think coffee like in your java maker. So a second problem i would like to find a better solution for is better probes for the LLC, because i think that's probably why it overfilled that once. The wires i'm using now are not copper, or magnetic, maybe their stainless steel? So i assumed they would stay clean and keep contact the best, but that one overfill has me worried. What's the best alloy to use in heavy water, that won't corrode? I was thinking maybe tin/lead solder over the bare wire tips might be help keep a connection in real hard water?

    Got anymore good ideas? :)
     
    Last edited: Jun 14, 2012
  4. DIYer

    DIYer

    12
    0
    Apr 30, 2012
    hmmm,.... i just thought of something i think might work, and cost pennies. Maybe i drill a hole in the container, then use a balloon to seal the hole. Water gets too high it pushes the balloon out a bit, and i could use that horizontal movement (since i have no room for a vertical float) to connect two wires that would activate the shut off valve.
     
  5. dssteven

    dssteven

    47
    0
    May 9, 2012
    That sounds pretty sketch to me. Kapp has some very solid ideas and although they may cost more than a baloon they will hold for a lot longer and give you much better reliability. My personal favorite was this:

    Put quite simply, even if you don't have the resources available now, wait until you do because even if the balloon trick would work, it would not last long. Just my opinion but an opinion from experience... trust me don't be *too* cheap. :)
     
  6. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    They are still some of the most reliable method to detect and control fluid levels...

    I do like like Harald Kapp suggestion of ultrasonic, it's no contact solution so no risk of 'scum' build up that will occur with anything placed in contact wit the water... And you can get the prebuilt modules dirt cheap, that offer decent resolution...
     
  7. DIYer

    DIYer

    12
    0
    Apr 30, 2012
    A prebuilt ultrasound detector module to measure the water level dirt cheap? I'm down for that, but Google isn't being my friend ATM. Where would someone procure such a device?

    I scrapped the balloon idea because i don't want to drill into the container, but for the time being, (because i need a fail safe so i feel i can leave the home) i'm building a float specific for my needs out of some wine corks and pvc tube. I ran a wire through the cork, soldered it to a nickel on top, cut a slit down the side of the tube for the wire to slide up and down with the floating cork, all metal will be out of the water. A big metal flat washer glued on top of the pvc tube has the other wire soldered to it, so as the cork gets too high, presto connection is made. Cost me a whole nickel. So you're right dssteven, I'm being way too cheap here, lol

    I've had problems with small floats i bought just flat out working intermitently at best, thus why i used big flat surfaces to bridge the connection with the one I'm making, hopefully it'll work till i can find something even better for cheap.
     
  8. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Ebay for the ultrasonic modules, you will need a circuit to drive them though...
     
  9. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    Why are you worried about price if you are dealing with heavy water?

    Washing machines use a pressure switch to control the fill. One of these could be used.

    A normal ball valve lever with a magnet actuating a reed relay would be my preferred solution.
     
  10. DIYer

    DIYer

    12
    0
    Apr 30, 2012
    Well, like i said, I bought an extra LLC as a backup, so i have a solution for $40 sitting here,.. so by default thats my high price point for this part of the project. But it's a simple task and shouldn't cost nearly that much to do reliably. I've never used an ultrasonic module before, and since their like $1.50 i wan a try one, seems cool as hell. I just gotta figure out which is the right one to get and how to power/wire it to i guess flip the 12v relay?.. hmmm
     
  11. Harald Kapp

    Harald Kapp Moderator Moderator

    11,164
    2,550
    Nov 17, 2011
    Last edited: Jun 14, 2012
  12. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    There are two common types of modules...

    One kind outputs a number via a serial line that represents the distance...

    The other kind waits for a request (small pulse) and then outputs a high pulse back to you, you measure the duration of this returned pulse to get your distance...

    You need an additional circuit to measure the returned value and do the switching when the proper distance is returned...
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-