Pool water level stabelizer

[rybitski]

below I have attached a diagram of my idea.
When it rains my father's pool starts overflowing with water so he has to go out and hook up the sump pump and let it run for a while. Sometimes he forgets that it is running and he pumps too much water out. So my idea was to make a switch to turn the pump off.

The switchis going to have pvc around it to deflect the waves and keep the pump from turning on and off all the time. I need to know what wouln be the best switch to use. The switch will have to be water proof becasue it will more than likely get wet.

I also need to know of the best type of relay to use. The pump will reguire no more than 10-15 amps. I was thinking about using a solid state relay but those tend to be more expensive...

If you have any better ideas please let me know.

[Enac]

Google "float switch". I found some inexpensive ones, and plans for a homemade one.

[rybitski]

A 'float switch' isn't exactly what I am looking for/need. From what I can tell float switches are for turning on pumps when you have 2 feet+ of unwanted water. I need a switch that turns on/off with 4-6 inch precision.

[Cabwood]

What about a mercury tilt switch? It won't corrode since it is encased in glass, and it has inherent hysteresis which would help reduce erratic switching from small waves.

[Cabwood]

Or - perhaps even better - use a magnetic reed switch, like those used in alarm systems to detect an open door or window. I imagine you could float a magnet on the water inside the pipe, and place the reed switch in a fixed position above it. These too are sealed and exhibit hysteresis.

[rybitski]

A mercury tilt switch like in an old thermostat? I don't think that would work because if it is colder then it would take a higher water level to turn it on, or reverse if it is hotter. that would be good if the mercury didn't change with temperature changes.

[rybitski]

would it hurt anything if I were to just use 2 metal rods so that when the water got high enough the 12vdc flows from one electrode through the water to the other? 12vdc isn't enough to hurt anyone any way as long as it is at a low amperage, right?
it would look something like this, but it would still be encased in the pipe to keep the waves away.

[Cabwood]

A mercury tilt switch is a glass tube in which mecury is free to flow from one end to the other under gravity. At one end are two contacts which the mercury flows over, closing the circuit. This has nothing to do with temerature, and everything to do with position.

What's wrong with the magnetic reed switch solution? This would be my preferred option, in this situation, for its simplicity and availability, and because there are no exposed electrical contacts.

You'll not get enough current to flow between two exposed electrodes (as you suggest) to trip a relay. Besides, the electrodes will corrode over time, especially with DC flowing between them.

[rybitski]

very true about the corosion...
Where would you get a mercury tilt switch or a magnetic switch? How much would either be?

[Cabwood]

Now I think of it, mercury in a swimming pool isn't a good idea. Stick with the reed switch idea, or use a tilt switch with a ball instead.

Google has all the answers you wll ever need regarding "tilt switch" and "magnetic reed switch".

[MP]

Rybitski,
You would want a little more control than that, but you have the idea. Here is one example.

MP

[rybitski]

Thank You for your input, but I have a question. Why would you need2 transistors, why not just one? why do you need them in the first place? I understand what a transistor does, but I don't understand why I need one for this project. Please explain.

[MP]

A couple of rods in the water will not be a reliable trigger for your circuit. There are two parts to the circuit here. One part is the trigger from the pool water. The other part is the control switch to turn the relay on and off.

Also, I am not sure where I got this drawing. There is certainly room for improvement. One is the need for a protection diode at the relay.

MP

[rybitski]

Sorry for the confusion, I'm not going with the metal rods anymore, was just an idea. They would eventualy corrode to the point where it was polluting the water and live current in a swimming pool just doesn't sound appealing...

My previous post shows the updated idea. using a switch I wouldn't need to use the transistors, right?

[rybitski]

Updated float switch:
Reed switches and whatnot still aren't water proof so I came up with this design. nothing has to be submerged.
Idea:(look at picture)
switch is off when depressed and on when not depressed.

[MP]

I'm not sure how you were going to connect a switch, but DC voltage will not hurt anyone in the swimming pool. A good finish on the electrode will allow it to last for a long time. If you connect a float to a switch, you would not need transistors. However, I tend to worry when someone talks about switches and live mains around a swimming pool. If you have mains anywhere near the pool, be sure to use a "Ground Fault Interrupter" circuit. I would certainly make sure the mains are not near the pool water. Switches have a tendency to arc when they are triggered.

The mercury switch mentioned above is not a bad idea if you do not want to make a circuit. It would certainly be a good low maintenance, low cost solution to take care of this problem while the pool is unattended. Mercury switches usually come as a floating device on the end of an insulated wire cable. When the level of the water changes the angle of the float, the mercury switch inside the float changes state. It either turns the circuit on or off. Still it is something that you would not want in the pool while you are using it.

MP

[rybitski]

the mains are now where near the pool, 20 feet or so away, and they are already gfic equiped. The only live wires would be the two wires carying the 12vdc.

When you say propper finish, what do you mean? What finish can you put on metal to keep them from coroding and still be conductive?

come to think of it it would be a very good idea to take it out of the water while you were swimming so it doesn't cause it to go on and off all the time...
I came up with the idea to hinge the sensor aparatus... here is a picture:

I'm sorry this is project is kind of random in the way that I continue changing the design... I guess I'm still in the brainstorming process.

[MP]

I see no problem with it. I assume you would use a float type switch? Something like this? http://www.homesecuritystore.com/ezStore123/DTProductZoom.asp?productID=1075
You know, if you find something on the market that you like, you can go here: http://www.uspto.gov/patft/index.html
to find all the information regarding the patent on it.

In regards to metal finishes, most hard finishes will withstand a lot of abuse before corroding or rusting. Anodized rods or chrome plated rods are still conductive. Actually, you can purchase special probes, but they cost much more than a home-made one.
I like the brain storming part of your project. It is always good to get many ideas out in the open before destroying materials on the workbench. Normally, you will find that there are a lot of ways to proceed. Then it is a matter of preference, and sometimes, cost.

MP

[rybitski]

I really like the design of the switch you sent me, but I'm thinking I could make something like it myself. A reed switch was suggested earlier, but I wasn't thinking how easily it would be to seal it in a waterproof case. I think I could seal it in hobby resin, or even a big glob of hot glue. Put a magnent on a float inside the pipe and cover the bottom end om the pipe with a mesh or something so that water gets in but the float doesn't fall out.

I'll be thinking on this more... Thank you MP!

[Cabwood]

Electrode corrosion would occur, almost certainly, not due to oxidisation but to electrolysis. To avoid this, the sensing current would have to be A.C., which really complicates matters from a design point of view.

My money is still on the reed switch - fix it to the pipe interior, and float a magnet on the water underneath it. As the water level rises, the magnet rises too, approaching the switch. At a couple of millimetres distance or so from the switch, the switch will close, energising the relay, and switching on the pump. No fancy circuitry, no moving electrical parts, no underwater connections and no worries about corrosion.

[MP]

You're not going to see electrolysis effects for a long time. The chlorine would have a bigger impact than electrolysis. In fact, chlorine is going to be harsh on a reed switch. Also note that a floating magnet setup will act erratic. Instruments that use a reed switch and magnet have the reed switch fixed and the magnet movement is controlled so that it is always the same reed switch/magnet interface each time. When you do not control this mating of the components, you have erratic switch action. Best to use a float ball with an arm and use the controlled pivot point of the float arm for this.

MP

[rybitski]

The reed switch would be no more erratic than the metal rods...

[ante]

My experience with sensors is: use stainless steel rods and AC voltage for sensing.

Just my two cents. ;)

[rybitski]

What setup would you use to trigger the relay, and what relay would you use?

[Cabwood]

A sealed reed switch won't be affected at all by corrosion or electrolysis. It's easy to find glass encased ones, and as for the solder contacts outside, a bit of silicon glue will seal them nicely (just be careful when soldering glass reed switches to avoid cracking them open).

The magnet/switch mating is critical in door/window sensors because the magnet is weak. Stronger magnets can trip a sensitive reed switch from several centimeters away. This application does not require a very strong magnet or a very sensitive switch.

As I said, with no moving parts except for the floating magnet, this solution is easy to implement, and the wiring is supremely simple - reed switch and relay coil, powered from 12V DC (or less).

As for the assertion that this setup would be more erratic than the electrode idea - WHAT? Electrodes will sense a closed circuit the instant water bridges them, and any wave (even tiny ones) could potentially cause opening and closing at ridiculous rates, until the electrodes are well and truly submerged. Either the pump or relay would soon pop without some kind of timing circuit to reduce switching.

The hysteresis in reed switches (or even mechanical switches) eliminates the need for complicated timing or hysteresis circuits, and would end up much, much less erratic than a basic electrode setup.