I have designed a sink for my garage that uses two 55-gallon emergency water drums as the water source (they are stacked on top of each other so I have 100 gallons of water reserve). I wanted the tanks to auto-fill from an ice maker water line I tapped into the back of the washing machine (which happens to be located just behind the wall). To make this work, I have installed a simple N/O (normally open) floater switch in the top tank to guage when the tank is full. I have attached it to a 12v N/C solenoid which controls the water flow to the top of the tank. In theory, when the floater switch is “open” (aka the tank is not full), it triggers the solenoid to allow water to flow into the top of the upper drum. Once the drum is full, it triggers the float switch and turns off current to the solenoid. The system works exactly as planned except I have one small glitch...

When the water tank is nearly full, the float switch sometimes opens/closes rapidly (probably due to water movement within the tank), which causes my solenoid to pulse on and off until the float switch finally settles down and remains an open circuit. I don’t like how the solenoid pulses like that, so I am looking for a simple circuit I can connect to the solenoid that will filter out the rapid on/off signal received from the float switch, until the switch remains in a constant “open” position for longer than a few seconds. Does that make sense? I can send photos/basic schematic of my system if that helps. Thanks for any guidance I could get.

 

Welcome to AAC!
How much current does the solenoid coil draw?
AC or DC solenoid coil?

 

You need to have two float switches, one to turn it off on full and the other to turn it on when the water falls a few centimeters (or inches). To implement this you will need a relay between the float switches and the solenoid. The lower switch turns the relay on and the relay must also then supply voltage to its coil (self latching). The top float switch would have to be closed until water is present. On opening it removes voltage from the relay coil. I'm not where I can get to my tools or I would draw a schematic.

 

A simple non electronic fix would be to isolate the float. This is done in some fuel tanks. A PVC pipe that is open at the top and bottom in the tank with the float working in the tube is one way of doing it. The tube keeps the movement of the water isolated but the open ends of the tube allow the level to be measured.

 

You need to add hysteresis to your circuit. One way is to use two float switches. One at the top of tank and a second a few cm below it

When the bottom switch turns off, latch the power to the solenoid on. When the top switch turns on, latch the power to the solenoid off.

The circuitry for this is fairly simple. An SR flip flop, an inverter or two, a couple of resistors and a MOSFET would do the trick.

A final design depends on a few things

• The float switches. Do they switch line power or can you route low voltage through the switches?
• The solenoid. What’s the power and amperage specifications.

 

Welcome to AAC!
How much current does the solenoid coil draw?
AC or DC solenoid coil?

My full circuit is 12V DC running from a small 12V ((2A) transformer I have plugged into the wall under the sink. The solenoid is 12v with a power rating of 4.8W. The floater switch has a max. contact rating of 10W, hence why I didn’t install a relay in the circuit. I believe the switch could handle the low current flow from the solenoid.

 

A simple non electronic fix would be to isolate the float. This is done in some fuel tanks. A PVC pipe that is open at the top and bottom in the tank with the float working in the tube is one way of doing it. The tube keeps the movement of the water isolated but the open ends of the tube allow the level to be measured.

Hmm. That might help! I’ll see if I have room in the top of tank to run a piece of PVC around the float. The float is one of the those simple stainless vertical rod floats, so this might work.

 

You need to add hysteresis to your circuit. One way is to use two float switches. One at the top of tank and a second a few cm below it

When the bottom switch turns off, latch the power to the solenoid on. When the top switch turns on, latch the power to the solenoid off.

The circuitry for this is fairly simple. An SR flip flop, an inverter or two, a couple of resistors and a MOSFET would do the trick.

A final design depends on a few things

• The float switches. Do they switch line power or can you route low voltage through the switches?
• The solenoid. What’s the power and amperage specifications.

Thanks for the info. See my earlier response on the specs for the float switch and solenoid. I believe I have room to install a second float switch slightly lower than my other one. Could I get some guidance on what the circuit would look like and the recommended sizes for the components? Thanks!!

 

Hmm. That might help! I’ll see if I have room in the top of tank to run a piece of PVC around the float. The float is one of the those simple stainless vertical rod floats, so this might work.

Hope it works for you. If this is for emergency water, why even use a solenoid valve? A toilet tank valve would do it mechanically, and work in most emergencies for a longer amount of time. Usually electric goes out faster than municipal water flow does. So by doing it mechanically you would have water for a much longer time.

 

Hope it works for you. If this is for emergency water, why even use a solenoid valve? A toilet tank valve would do it mechanically, and work in most emergencies for a longer amount of time. Usually electric goes out faster than municipal water flow does. So by doing it mechanically you would have water for a much longer time.

I didn’t have room for a mechanical valve inside my tanks. They are your basic blue 55gal emergency storage tank with two small 2 in. openings in the top, hence why I went with the 12v solenoid system. If there was an emergency and I needed to re-fill the tanks, I could override the 12v solenoid with a 12v motorcycle/atv battery to fill the tanks over and over. Great thoughts though, thanks for sharing.

 

Municipal water utilities use pressure transducers to determine the level. If you wanted an electronic version you could try that and build the hysteresis into the circuit. The circuit could also provide an indication of the level in the tanks.

 

Some of the float switches have a simple reed switch, if switching a solenoid direct, you may need a BEMF diode across the coil otherwise the switch may not last long.
See ebay 254215823837 for dual level switch.
Max.

 

Thanks for the info. See my earlier response on the specs for the float switch and solenoid. I believe I have room to install a second float switch slightly lower than my other one. Could I get some guidance on what the circuit would look like and the recommended sizes for the components? Thanks!!

Sure, as soon as I get home

 

Sure, as soon as I get home

As a sneak preview, my initial post got simpler. All you need is...

• CMOS Quad Dual Input NAND Gate (CD4011)
• Diode0
• 0.1μF capacitor
• MOSFET (specs TBD)
• 10K resistor (specs TBD)

And two float switches, closed when water level is below switch mounting. Oh, I assumed a 12VDC power source.

 

Here is a relay based design:

S1 and S2 are both normally closed float switches. S2 is located lower than S1, S1 is at the top. When water is low S2 is closed and applies power to the relay coil causing the coil to latch and applying power to the solenoid (far right). When the tank is full S1 opens and power is removed from the relay.

 

Don't you have room for this type of valve?

 

Here is a schematic. The resistors on the logic input can be 1/8W. The pulldown on the MOSFET can be a 1/4W.

This assumes that the float switches are NO when the water level is at or above them. And that they switch +12VDC when the water level is below them.

The logic gates are from a CD4011 quad dual input NAND gate. It’s operating voltage can be as high as 18V; it will operate fine with 12VDC. The circuit used three gates. The fourth should have its inputs tied to ground and nothing connected to its output.

The MOSFET is a logic level N channel MOSFET - an IRL540.



I forgot to draw a 0.1μF capacitor connected between the 4011 Vcc and Gnd pins.

 

Here is a relay based design:
View attachment 180151
S1 and S2 are both normally closed float switches. S2 is located lower than S1, S1 is at the top. When water is low S2 is closed and applies power to the relay coil causing the coil to latch and applying power to the solenoid (far right). When the tank is full S1 opens and power is removed from the relay.

I did some more research on Hysteresis and came across this same diagram using a relay approach. I really like it for my specific application and so this is how I implemented my solution. Thanks for your input!

 

Thanks djsfantasi for your quick response. This is awesome. I did however go with the relay approach for my particular application, but I really appreciated your input getting me pointed in the right direction with adding hysteresis to my system.

Greg S.

 

I did some more research on Hysteresis and came across this same diagram using a relay approach. I really like it for my specific application and so this is how I implemented my solution. Thanks for your input!

You are welcome.