Wiring a float switch to stay open

Thread Starter

vernwellstein

Joined Feb 7, 2019
7
Hi, I have a very similar situation to the one found in the post below:

https://forum.allaboutcircuits.com/threads/float-switch-wiring-w-dpdt-relay.129486/

Please note that as in the case of the original poster of the post above, I have very limited knowledge concerning electronic circuits.

I'm planning to install a float switch to get a pump (220V/2HP) to shut down when it has finished filling a 500 gallon tank. Due to water fluctuation, it is possible that the switch turns on and off repeatably before the water level stabilizes, which could damage the motor. Therefore, I need some form of latching mechanism. After researching the topic, I came up with the following diagram. I based myself on the solution proposed by Dodgydave in the thread linked above, but I'm not sure if I fully understood his answer.

circuits.png

In short, what I wish to know is if my diagram is correct and whether or not there is a simpler/better solution that would meet my requirements. Also, I'm planning to purchase the following items (or similar pieces) to build the system. Would these do the job or are they the wrong parts?

The 220V/12V SPDT? relay:
https://www.amazon.ca/Yeeco-Contactor-Switching-electrical-switches/dp/B00R7SYKKO

The 12V/12V SPDT relay (if i was to use a 12V adapter, how much WATT would I need?):
https://www.amazon.ca/Ehdis®-Truck-Normally-Socket-Automotive/dp/B01KFKEFZA

The float switch:
https://www.amazon.ca/URBEST-Aquarium-Liquid-Sensor-Stainless/dp/B01CECHJFK

Thank you in advance for your time and your help.
 

ericgibbs

Joined Jan 29, 2010
13,652
hi vern,
Welcome to AAC.
One method I have used is a 'stilling tube'.
The float is located inside the tube, the tube has a number of small holes drilled along its length.
The idea is the tube/holes control the rise/fall rate of the water and the so the float is buffered from the outside splash/slushing of the fill water.

This method is/was used on Tidal water measurement to reduce the sea wave action on the float, sometimes called a 'stilling well'

E
 

Yaakov

Joined Jan 27, 2019
3,521
Excellent advice from experience by @ericgibbs, I will add one other bit from experience: don’t rely on one sensor. Add a failsafe sensor somewhere above max level so if (when) the normal sensor fails, the backup can kill the pump. Make sure you include an alarm indicating the original sensor failed.

Or, invest in a really big wet/dry vac and keep it nearby...
 

Tonyr1084

Joined Sep 24, 2015
6,269
Welcome. And very well written post. You show a lot of understanding with postings here. Do you have another account on AAC? Hard to believe this is your very first post. Nevertheless, welcome. Hope we can help you solve your problems.
 

Thread Starter

vernwellstein

Joined Feb 7, 2019
7
Thank you for the advice. It makes sense to have two sensors, and the stilling tube idea is great. I originally planned to add an alarm for the first sensor, I could probably also include two LEDs to indicate the state of the sensors.

I also came up with another circuit design that uses a DPDT relay. I think I got it right this time. I also would be interested to know if it makes a difference if the switch is connected to high (120V) or low voltage (24V). Can it impact its durability. From my research, I know that connecting it directly to the motor circuit is usually not advisable.

circuitsSingleRelay.png

Relay I would now plan to use:
Packard C230B 2 Pole 30 Amp Contactor, 120 Voltage Coil
https://www.amazon.ca/Packard-C230B-Pole-Contactor-Voltage/dp/B001KGSJ74
 

MrSoftware

Joined Oct 29, 2013
2,015
For a mechanical solution you can put the float inside a bucket about half way from the bottom, with a flapper valve on the bottom of the bucket that allows water out but not in. As the water rises the bucket remains empty, the float does not move. When the water level surpasses the top of the bucket, it will fill rapidly, quickly submerging the float switch completely. As the water goes down the bucket will empty through the flapper.
 

Thread Starter

vernwellstein

Joined Feb 7, 2019
7
Welcome. And very well written post. You show a lot of understanding with postings here. Do you have another account on AAC? Hard to believe this is your very first post. Nevertheless, welcome. Hope we can help you solve your problems.
Thank you for the comment. This is indeed my first time. However, whenever I start a project, I tend to research it intensively, often giving the impression that I know more then I actually do. Although I do learn a lot in the process.
 

Tonyr1084

Joined Sep 24, 2015
6,269
Years ago I replaced a toilet tank fill assembly unlike the regular ones with the arm and ball or the float and the valve. The one I recall was a pressure sensitive device that sat at the bottom of the tank. As the weight of the water increased beyond a set point the valve would close (mechanically). I'm also thinking about washing machine switches that you select the size of the load by mechanically changing a lever that changed the spring tension on a valve. When the water was high enough (heavy enough) the switch would activate and shut off the water flow. The problem with both of these possible considerations is that when water level dropped a little the valves can open and again re-fill the tank. It may take a little more circuitry to detect water levels and control the pump. But I offer it as one potential solution - the old washing machine fill control valves. The one connected to the bottom of the tub via a hose that runs up into the control box on top of the washer where you select the desired water level. I've not messed with them other than in passing and I wonder if they have a hysteresis. If so it MIGHT be just the ticket to controlling the water level in your tank.
 

Tonyr1084

Joined Sep 24, 2015
6,269
Did a search on Amazon. Found This

I don't know if this has a varying output or if it's a mechanical switch type. Judging from the second and third views there appears to be an adjustment screw on the housing. I'm thinking IF this is a sensor and not a switch it could be incorporated into some electronics to sense what level you want a circuit to activate a pump and at what level you want the circuit to shut it down.
 

Reloadron

Joined Jan 15, 2015
6,065
Years ago I replaced a toilet tank fill assembly unlike the regular ones with the arm and ball or the float and the valve. The one I recall was a pressure sensitive device that sat at the bottom of the tank. As the weight of the water increased beyond a set point the valve would close (mechanically). I'm also thinking about washing machine switches that you select the size of the load by mechanically changing a lever that changed the spring tension on a valve. When the water was high enough (heavy enough) the switch would activate and shut off the water flow. The problem with both of these possible considerations is that when water level dropped a little the valves can open and again re-fill the tank. It may take a little more circuitry to detect water levels and control the pump. But I offer it as one potential solution - the old washing machine fill control valves. The one connected to the bottom of the tub via a hose that runs up into the control box on top of the washer where you select the desired water level. I've not messed with them other than in passing and I wonder if they have a hysteresis. If so it MIGHT be just the ticket to controlling the water level in your tank.
I did same about 15 years ago and that valve worked so well I just got another for another toilet. As to washing machines check this thread out and what LG is now using.

Ron
 

Thread Starter

vernwellstein

Joined Feb 7, 2019
7
Thank you all for your input so far. Using a pressure sensor could be a solution, however I believe it may be more complicated to adjust then a simple float switch. Some of the float switches found on the link provided by Reloadron are equipped with 'splash guards' which seem to be the same as the previously mentioned 'stilling tube'. Taking all this in, I drew up another plan.

I'm still unsure about the power supply for the relay/contactor circuit (could be 24V or 110V), and whether or not the circuit itself will latch as intended.

circuitsStilling.png

I could always use an SSR relay and give up on the latching mechanism; however, I'm not sure to what extent I can trust the 'splash guards' to eliminate false switch activation.
 

MrSoftware

Joined Oct 29, 2013
2,015
If a pressure switch is an option then that would be a good way to go. They are easy to adjust. There are 2 adjustment screws, but you probably only have to fiddle with one, if at all. I grew up on well water and we use pressure switches on the pumps. Here's an example:

 

Yaakov

Joined Jan 27, 2019
3,521
You might consider using a time delay relay to lock out the pump power for a fixed time after the switch kills it to avoid the oscillation. You can use empirical observation to decide on the delay require for the float to stabilize.
 

Reloadron

Joined Jan 15, 2015
6,065
Given a choice I would likely use a circuit similar to the below.
Pump Level Switches.png

This assumes the use of float switches rather than a pressure switch. The upper circuit is either 12 or 24 VDC as I was never fond of running higher voltage AC in water tanks. The lower circuit can be the voltage of your choosing for the pump motor contactor. When the N/O lower switch closes on low tank level RY 1 will latch through a N/O set of its own contacts. RY 1 is a DPDT relay having a low DC coil voltage. When the tank upper level is reached the circuit is open and will remain open till the process repeats.

I also like using pressure switches to sense a tank level and it generally comes down to which approach is the practical for a given set of conditions.

Using either method I would include a mechanical fail safe switch and test it maybe monthly.

Ron
 

Thread Starter

vernwellstein

Joined Feb 7, 2019
7
Got everything running. Thank you all for your help. At first, I was unable to get the relay to activate. So I tested each parts separately and realized that the alternating alarm that I was using caused the relay to fail, probably because it shuts itself on and off every 2 seconds. So a rewired things slightly differently. Here is the final diagram, hopefully it can help others in the future.

circuitsLatchingRelayFinal.png
 
Top