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Float switches in series and a relay on a timer to trigger a pump.

Thread starter #1
Hi all,
I'll just take a bit of time to explain what I am trying to achieve. I am a novice when it comes to electronics, and only have very basic knowledge, so any help at all would be awesome.

I would like to build a 12V circuit which detects a rising water level (using a normally open float switch) in order to trigger a small pump to take periodic water samples (pump on for 5 seconds, off for 600 seconds), for as long as the float switch it closed. When the float switch falls back down (i.e water level decreases) i want the cycle of sampling to stop completely until the next time the float switch is raised.

Additionally, I want a normally closed float switch located in a container which the water is pumped into in order to detect when the container is full and cut the power.

Here are my components:
1x N/O float switch - 1A
1x N/C float switch - 1A
1x Timer relay module (CE030) manual here: http://files.banggood.com/2016/SKU404333.pdf (this module has multiple programs built-in)
1x Micro pump - 350mA draw
1x 12V 9Ah battery

I managed to achieve the above by placing the two float switches in series BEFORE the timer relay module, so that if the N/O float switch is raised, power reaches the Relay module, but ONLY if the N/C is down at the time. If at any time the N/C float switch is triggered (floats up), the circuit is opened and power is cut to the relay module. the programs on the relay module are preset so it is only a matter of changing the timing to achieve the cycle i want.

However, i seemed to have blown up the N/C float switch after about 10 operations of the cycle. I don't believe it was a faulty switch, so I have i overloaded it or something? the switch is rated to 1A and the pump only draws 350mA, so i thought it would work.

One last question: I have a different timer relay module which has a "trigger in" terminal. I wired the float switch into this terminal and the trigger worked, however when the float switch became open (water level decreased) the cycle continued. It only stopped after the float switch was triggered again. Obviously this is not ideal because when the water level rises again the cycle will stop. is there anyway around this apart from having the float switch between the battery and the relay module?

Apologies for the long post, I'm hoping someone can give me a bit of help with this. Any tips about how to achieve the above would be really appreciated.
Thanks, Chris


Well-Known Member
Most Helpful Member
A motor that draws 300mA running probably pulls a couple amps at startup.
I am using a float switch like the picture. It is built for 120/220vac but DC will work. I am using a 1 horse pump.
More types:
1550184526719.png 1550184493410.png

I do not understand the need for two switches.
Thread starter #3
Thanks for the quick reply.
The scale of this project is quite small, so my float switches look more like the below picture.
The container i am filling will only be about 1L, and is located inside a waterproof compartment. I need to cut the power once this container is full so it doesn't overflow. The other float switch (N/O) is located outside the compartment on the ground. When rainfall causes the water level to rise, it is triggered and begins to fill the container using the cycle of 5 seconds on, 600 seconds off. Once the container is full, I need the power to be cut so that the bottle does not overflow.
For context, I am trying to create a device that takes a composite water sample of agricultural runoff to determine what chemicals and nutrients are moving into nearby waterways.

I suppose it is like a High/Low level system for a water tank, however the low level float switch is located outside the tank.

Thanks again

Nigel Goodwin

Super Moderator
Most Helpful Member
So thats whats in them float switches with a ball inside.
Yes, I replaced a round float switch last year (like the one in post #2, with the blue circle on it), I obviously cut the old one open, and it was just a steel ball and a micro-switch. Needless to say I kept the ball, for no good reason I suppose, but it was too nice to throw away :D


Well-Known Member

A wiring diagram would help ,but it seems like you are passing the full motor current though the float switches which is not a course I would take.

Having the floats as inputs only to whatever your timing device is always a better way.

My approach would be to use a cheap Arduino Nano clone board , around £3 and just use some simple coding to produce the actions you need, driving the motor with a simple transistor and/or relay.
That would also use a lot less current than the module you show, so meaning longer battery life.

Also if using something like the Arduino means you can also readily use some of the more modern fluid level devices like these two below, which having no moving parts so possibly more reliable .

The optical one is accurate to about 1.5mm and the stick-on external one is about 3-4mm. ( using them myself).


dr pepper

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I've changed a few but never cut one open, but I will next time, ball bearings are handy for making gaskets.


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Most Helpful Member
I have a different timer relay module which has a "trigger in" terminal. I wired the float switch into this terminal and the trigger worked, however when the float switch became open (water level decreased) the cycle continued. It only stopped after the float switch was triggered again.
Try adding a 10k ohm or so resistor from the trigger input to ground.


Well-Known Member
hi, yes just like post 3 i set up a ebb and flow system using 2 of those 5v float switches an uno and relay board and 120v hardware such as power cords an plug sockets ... for larger pumps but would also work for smaller

i use the uno to time the flow cycles and debounce the switches ... without debouncing the switches are sensitive and the small waves cause the relays to go crazy
also i put in a wifi module for remote access and a status LED/.../the code could be simply modified to your purposes

btw just going off memory and what you described but i dont think those small ones are for 12v ...
Last edited:


Well-Known Member
Most Helpful Member
There's a simple, cheap solution to your problem.

Go back to your original arrangement of float switches and timer, but instead of switching the motor directly, connect a small 12 volt relay in place of the motor and use the relay to switch the motor.

Also, install a reverse-biased diode across the relay coil to kill back emf. Anything will work for this, including a simple 1N4148.

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