Newbie: Auto shut-off for water pump based on water-level

I think your schematic is beyond the abilities of a beginner that has never touched electronics. Even to me your schematic is a bit fuzzy, and I have had my feet wet in "basic" electronics for some time now... Isn't that a little extreme?

Mike

It's not clear to me how it works at *present*? What switches the pump off? And on again? Presumably you don't switch it on manually and then periodically traipse upstairs to see whether the tank is full?

Anyway, I reckon you could easily adapt this circuit I suggested a while ago:

Just remove Float switch 1 for the extra 'reservoir' that was needed in that aquarium application, and the associated components D1, D2 and R2.

If you'd prefer to use an NPN transistor to drive the relay, use pin 3 instead of pin 4.

This is just a simple bistable circuit, edge-triggered by the float switches so that it latches into an appropriate state until the alternative switch is triggered.

You don't mention any need for a second float switch (hence my question about how the pump gets switched on at present). If you don't need one then you could replace that switch with a push-button to start the pump manually.

If you want an even simpler approach (or an added precaution), wire the supply to the motor relay through contacts activated by the float, guaranteeing that the pump cannot operate above a certain level.

And check your overflow pipe!

Take a look at Electronic Design, Nov 29,2004, page 90: "Simple Circuit Maintains Water Level Between Two Preset Limits". No floats needed!

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

I'd like to second the motion. Grainger has the Dayton 3BY58 for $22.84 USD, just as described in KT's response, which is made to switch pump motor loads (60 amp starting, 15A running). This is a trivial low cost solution to your problem.

Also:

• As a "newbie", you're going to have to be careful with the presence of water around electronics for various reasons, safety being the first. Starting out your career in practical electronics with a line voltage project isn't a good idea.

• In switching a motor, you may have problems with switch/contact arcing which might cause a complex circuit to be upset because of EMI

• Even if you do have an overflow pipe, something experimental that can cost you significantly usually isn't a good idea for someone new to the art. In the event of device failure, best case is an astronomical water bill. Worst case, a swamped house. Pass on this one.

Look up the device on the Grainger site and see if you can find anything like this locally -- I don't think you'll have any problem:

I'm not trying to sound harsh, but if you'd just like to try a simple educational circuit "to get your feet wet", look at something else.

Good luck Chris

There is a float device you can get which looks like a flattened ball with a cable out of one end. You mount it with the cable tethered to the side of the tank. It has a switch built in which activates when the float is tilted downward from the cable end, ie: when the level is low. Connect a device like this to a small mains /motor rated relay and you have the whole problem solved. Regards, KT

Exactly; it's not electronics; unless you want to make it so! It's simple on/off switch logic; controlled by the water level.

Electricity flows through a normally 'ON' closed (in the low/empty position) float switch to actuate the pump. A true float switch will be designed to switch off and on the somewhat inductive load of, for example, a one third HP pump motor. Typically such a switch will last for 15 to 20 years, depending how often it cycles on/off.

Water flows to tank, float rises, when water reaches the level you have preset the float switch 'OFF' and opens the circuit and electricity ceases to flow to the pump. That in its simplest form is how it would work. The float switch may have some sort of mechanical adjustment so that after the water is at the level you want it is allowed to fall again to certain extent before the pump operates again to refill the tank. If float switch is too sensitive to the water level the float switch will operate the pump every time someone takes one cup of water! And the pump will operate too many times.

Also if the pumping rate is very fast/high and someone is running water continuously (to fill a bath tub say) the pump may fill the tank more quickly than the outflow so it will cut in and out several times. This may or may not be a problem for you? You may be able to adjust the pump flow rate with a simple water valve, to avoid that.

MOST IMPORTANT. Have a gravity overflow; very slightly above your desired water level! Something may misoperate; without overflow there will be steady flow of water over the lip of the tank down through the ceilings and house structure until pump is manually turned off. (BTW I've seen software that omits that kind of 'what happens if' thinking!). Also make sure the overflow can't (depending on your climate?) freeze shut/blocked! Or goes to a drain that cannot block or backup. That is the over flow pipe should be of sufficient size to handle the gravity overflow. Whereas the fill pipe from the pump is at pressure!

If it is undesirable to run household AC up to the float switch on the tank and thence down to the pump, a more complicated (perhaps low voltage ) circuit could be devised' that could operate a relay that would actually switch on the pump? But that means more components (I can think of at least three more electrical parts and more cost) and insufficient info is available about what you are trying to accomplish?

However I would comment that in all these situations 'The simpler the better'. If possible use standard and available parts. It's a waste of time to spend a long weekend trying to analyze why something doesn't work when a quick trip to the hardware store or building supplier, perhaps fifteen years from now, by someone will provide a most likely similar/identical standard float switch etc.

Sounds like this is a practical plumbing and float switch job.

Thanks everyone, this was enlightening...

My main motivation was not to solve the problem, but to learn some electronics. If the problem got solved, that's just a side-effect ;). So based on all of your kind input, i think i will change the project a bit.

I think i'll just hook the float to a rheostat or pot (i don't really know which at the moment) and hook the pot to an LED display which would be downstairs and would tell me about the level of water. I can turn off the pump manually with the help of the display. Surely, i hope this is electronics and not just plumbing ;).

Anyway, i'll read up on all these links and be back when i get stuck... Thanks once again...

HI, I would suggest a normal float valve to let the water into the tank and a simple pressure switch(RS Supplies) downstairs on the feed pipe to the tank.

Tank empty, = floatvalve open = no back pressure, = pump on.

Tank full, = floatvalve closed = back pressure = pump off.

Just a suggestion :-)

Kind regards, Gordon.

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Hi, I realize you want to build something yourself but you might try a marine store to get some ideas. They have all kinds of water activated/deactivated switches for pumps. Raul

One easy to find switch that might be ideal for his application is the water level sensing switch used on most washing machines. Although suitable for pilot duty only, a visit to any appliance junk yard should be rewarding. The cost, flexibility of application, and availability, should make one a good fit.

Louis--

Go to this site:

And do a search in the DIY forum. Reef tank folks (including myself) have discussed this quite a bit. I don't want to sound like I'm sending you somewhere else but there's so many different ways to approach it and issues to consider.

Personally, I use a float switch from grainger that controls a solenoid valve. I use it to let RO water into my tank. Some people take an extra step and use both a low limit and high level limit float switch. As mentioned previously simplicity is key since water + electricity a)don't mix and b)are prone to failure.

Kevin