Circuit for automatic switchoff when water in tank is filled

adigopula · Jun 19, 2005

Hi,

Can any one help me giving a flexible circuite, which swithchoff the AC Motor when the water in the over head tank is filled. This will help me in saving water from flowing from over head tank.

Thank You

D.J. · Jun 19, 2005

Hi,

I know theirs a way to do this becuase my dad did it when we had two big 5,000 gal. tanks that stored water from the well.

He had two probes stuck inside the top of the tank. One was really long and the other was very short. When the water was high enough to hit both, the long probe and the short one, the pump went off. When the water was low enough so it didn't touch any of the two probes, the pump turned on. The probes where just long pieces of stiff wire.

I know that the water had 12 volts applied to it the whole time.

Sorry I can't be of any more assistance

, I can't remember the rest of the circuit, but maybe you could build off this :?

D.J.

pike · Jun 19, 2005

All you need is a switch and a floating bouy, when the bouy floats up to the correct level, it hits the switch, which drops a relaly which kills the pump.

Simple

D.J. · Jun 19, 2005

That would probably be the simplist way

eblc1388 · Jun 19, 2005

But without some deadband, the motor will cut in once the water level drops a little. That's why two electrodes are needed in the example given above.

You need some forms of deadband to prevent the frequent start/stop of the pump.

chiba · Jun 19, 2005

Like pike said, just use a float switch to a low voltage relay. Here, i drew a picture:

**broken link removed**

You'd use an NC push button switch or micro switch so the relay would not be on when the tank is full.

Dr.EM · Jun 20, 2005

Like eblc1388 pointed out, there needs to be a means of preventing the pump switching on and off too frequently. I suggest fixing another switch arrangement to the underside of the bouy arrangement, so that only when that switch is activated will the motor switch back on. Seems like a counter circuit or at least some kind of simple logic will be required here.

Roboticinfo · Jun 20, 2005

REPLY

Here is a schematic

**broken link removed**

it beeps when it reaches it's limit.

Nigel Goodwin · Jun 20, 2005

Dr.EM said:
Like eblc1388 pointed out, there needs to be a means of preventing the pump switching on and off too frequently. I suggest fixing another switch arrangement to the underside of the bouy arrangement, so that only when that switch is activated will the motor switch back on. Seems like a counter circuit or at least some kind of simple logic will be required here.

The switch and mechanics will provide a degree of hysteresis anyway, but the existing float systems in your house (water tanks, toilet etc.) don't require anything extra?.

Just like those, the output from the tank is likely to be greater than it's input - so as you start using water from the tank the float will drop, and the pump will turn ON. However, the pump is unlikely to replace the water in the tank faster than it's being emptied (or why have a storage tank?), so there won't be any pump cycling problems. Once the water being used from the tank is turned OFF, then the pump will simply keep going until it's refilled, then be turned OFF by the float switch.

Why try and get complicated, when there's most probably no reason?.

Pommie · Jun 20, 2005

When I first arrived in Australia, I lived in a rental that didn't have mains water. Water was stored in a 20,000Ltr tank that was filled with rain water or, if it didn't rain, from a bore hole. The bore delivered about 1500Ltrs per hour and was about 30Mtrs below the storage tank (yes, it was a big pump). The output was definitely less than the input.

If this is the arrangement that the original poster has then a ball float is not the way to go and the 2 rod system above sounds like a good idea.

A simple way would be a timer - say 10 hours.

Mike.

john1 · Jun 20, 2005

Hi,

This is not really intended to be a practical arrangement, although
something similar probably could be practical.
It sort of popped into my mind when i saw the comments on simplicity
and complications.

I put it forward as a contender for the kiss prize.

Any takers ? ........... John

mstechca · Jun 21, 2005

Water conducts electricity. In fact, it has to if you are not supposed to pour water on your computer :lol:

So, the absolute, most simplest way to do it is to use any non-metallic container (a container which cannot conduct electricity).

In your circuit, you will have two long leads. Stick one at the bottom of the tank. Make sure the bare wire can reach the water.

Now, stick the other lead (or wire) at the highest point you want the water to go before the motor cuts off.

Now make an inverter with transistors (you can find it on play-hookey.com) and connect the battery, the inverter, the motor, and the water in series.

You might need to somehow give extra power to the motor, because it doesn't like to run on low power.

FRIED · Jun 21, 2005

An idea. The weight 1 on the right is equal to the weight on the left with weight 2 and float 2 submerged.

eblc1388 · Jun 22, 2005

A modified version of that by FRIED. But now it looks the same as that by John1.

FRIED · Jun 22, 2005

The idea does not rely on friction. It relies on mechanical advantage.
If, ignoring the weight of the floats, weight 2 is 500g submerged and the displacement of the floats are 300g then the submerged weight and float on the left side is 200g, and weight 1 is 200g. In position 1 weight 1 has full mechanical advantage and the other side has (45°) 1/√2 advantage = 141g, so is stable. (Relative moments) The same reasoning applies to position 2. Using a single float that slides will work as long as it weighs enough to tip the balance at low level, in this example more than 59g and has enough spare displacement above this at the high level to lift more than 59g.

mstechca · Jun 22, 2005

Why not just modify a toilet tank?

eblc1388 · Jun 22, 2005

FRIED said:
The idea does not rely on friction. It relies on mechanical advantage.

Oh, not referring to your design. I meant my "float" version depends on friction to work so is definitely not a good one to use.

heathtech · Jun 22, 2005

omega.com

I suggest going to the following: Omega.com and reviewing the good reference material and products available for level control. I use their products for temp,level,pressure,flow,and data aquisition at my job all the time. They have float assemblies that can be mounted in the tank with various combinations of N.O., N.C. switches that can be used to turn a pump on to fill the tank and shut it off when it is full. A relay doesn't even have to be used when using two switches. The length of they bouy's magnet can control cycling. Of course, Hysterysis and cycling could also be controlled using a time delay relay. There are several other alternatives including capacitance and conductivity sensors that can also work.

heathtech · Jun 23, 2005

pressure switch

another way to control level is with a pressure switch. Mount the switch at the bottom of the tank and adjust diaghram spring tension to tank head pressure level. deadband is introduced by the mechanical spring.

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