Pool water level stabelizer

[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.

 

[MP1]

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...

 

[ante1]

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.

 

[rybitski]

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

This is true, but it is also true for the reed switch. ( I like the reed switch idea)

Let's complicate things... Now we need some kind of circuit that doesn't turn on the relay unless the switch is closed for more than 5 seconds (or something like that).

 

[rybitski]

How about a timer circuit that when energizes times 5 seconds then sends the signal to the relay. After the circuit is de energized the timer resets and waits to repeat the process...
I don't know of a way to do it, but it is a theory...

 

[ante1]

There is no big problem using electrodes to control a relay. Just like an automatic bailout pump for a daycruiser a timer closes the relay 5 minutes or so after continuous contact between the electrodes, this will cure the problem. No rattling relays! But if using AC the electrodes can be partly submerged at any given time and the capacitance between them indicates the level.
If you like to avoid electronics, try the simple way with a reed switch. To get the pump start-to-stop range as wide as possible try to find a strong magnet, cannibalize one from an old hard drive they are very strong.

 

[rybitski]

It is not that I like to avoid elesctronics... but why complicate matters?

 

[rybitski]

Show us how you would build it, Ante. Please. ;D

 

[ante1]

Hi Chris,

Ok, the easy way: reed switch and magnet! This is very close to your original idea! Attach a magnet to a cylindrical float (plastic); put the float inside a tube (also plastic) which has an inner diameter just to fit the float. Close the bottom end of the pipe and leave the top end open and above the surface at all times. Attach a reed switch on the outside of the tube; make a small bracket which might be kept in place with a stainless steel house clamp for easy adjustment. Drill some small holes along the pipe (size and distance of the holes depends on the size of everything else) this will have a dampening effect on the float when you dive into the water or playing with your rubber duck. ;D

 

[rybitski]

What would be some appliances that have reed switches?
I found one in an old mac printer, but it was a normally closed reed switch.

P.S.
I'm a scavenger.

 

[ante1]

Well, reed switches can be hard to find also for dumpster divers! Try older copiers and faxes even in some old printer or buy one, they are not very expensive. 

 

[rybitski]

ah, I might have to buy one... I dunno I feel more acomplished (and rewarded) if I hind it in something someone was throwing away...

 

[ante1]

Yes, I know what you mean. If you Google ´reed relay´ you get an idea of how such a relay looks, there are many shapes and sizes. Sometimes you can pull out the glass element from this type of relay and use it for other purposes. If you find mercury relays or mercury wetted relays, just leave them and do not tamper with them!