How to setup two floating swicthes to run a pump...

[albertc30]

Hi all.

I have setup my shed with solar panel 25W 12V for the lights and it seems I am charging my 12V 22ah deep cycle battery in about an hours.

So remaining energy generated is being thrown away.

As such, I had another idea. Hot water in the shed to supply a tab in the garden to clean tools and wash hands.

Got myself a 25 litre tank, immersion heater element, temperature control switch, submersible 12v water pump and 2 floating switches.

I could have bought 1 long rood switch with two boys but did not and I could just use one switch and it would work. Only one issue. I would have about 25 litres of warm water and with about a 1 litre, maybe 2, of water displacement the switch would come on turning the pump on. The mixing of cold water and the hot water would result in cold water in no time. So, a second switch to actuate as a lower water level and start the pump, second switch at top to stop pump once full tank.

The setup of this is driving me nuts and now I am beginning to wonder it can't be done as such, not unless I use a relay. I have thought of it wired up in series, in parallel but as soon as the lower limit switch is above it's on level it will cut out, stopping the pump.

As a background, I have done a level 2 in electrical installations and am now halfway a 2 year course on a level 3 electrical installations. Circuits have been discussed in class along with relays but not in a bigger depth. I find all this very interesting and intriguing.

Any help and / or advise is well and truly appreciated.

Much appreciated for your time.

Regards,
Albert

 

[barry]

Your description is a little hard to follow, but it sounds like you want one switch to turn the pump on at low water level, and second one to turn the pump off at high level, is that correct? You will need a relay to do this. Here's one way: wire your relay coil across your motor. Your low-level switch is normally-closed (when the level is high, it's open); this switch is in series with one leg of the motor/relay. In parallel with the low-level switch you would have a normally-closed relay contact in series with the normally-closed high-level switch (opens when the level rises).

Thus, if the level is low, both float switches are closed, and the motor and relay are engergized. The relay contact in series with the high-level switch keep everything energized even after the low-level switch opens with the rising level. When the water rises and opens the high-level switch, everything turns off and the cycle starts again when the water level drops.

 

[BradtheRad]

I could have bought 1 long rood switch with two boys but did not and I could just use one switch and it would work

Did you wish to do this the way a sump pump is switched on and off?

The long rod needs to have some friction on it. A single buoy, rising and falling, can control the pump.

The rod needs to be the correct weight, and the friction must be just right, so the buoy will lift and drop the rod at the extremes of water level.

The sump pumps I worked on had one switch, with spring action built into it.

 

[albertc30]

Your description is a little hard to follow, but it sounds like you want one switch to turn the pump on at low water level, and second one to turn the pump off at high level, is that correct? You will need a relay to do this. Here's one way: wire your relay coil across your motor. Your low-level switch is normally-closed (when the level is high, it's open); this switch is in series with one leg of the motor/relay. In parallel with the low-level switch you would have a normally-closed relay contact in series with the normally-closed high-level switch (opens when the level rises).

Thus, if the level is low, both float switches are closed, and the motor and relay are engergized. The relay contact in series with the high-level switch keep everything energized even after the low-level switch opens with the rising level. When the water rises and opens the high-level switch, everything turns off and the cycle starts again when the water level drops.

That is correct mate.

I have never used relays in the past so this will be my first go at it.

Any advice?

My floating switches only support a max load of 0.5A I guess any 12V will do given they only use about 100mA?! However, the load, the water submerged 12V pump, draws 3A.

Thanks for the great help/advice given and for the time taken to help myself and others.

Regards,
Albert

 

[barry]

Okay, so my description won't work since I expected the switch to pass the motor current. You would need a relay with TWO sets of contacts. You would still use the circuit as described in post2, except the motor would be wired in series with the second contact and 12V. Sorry, I'm too lazy/busy right now to draw a schematic, but if you're having trouble visualizing it, ask. Any relay with a 12VDC coil, less than .5 A, and contacts rated for 5A or greater should work. For example (one of millions): TE Connectivity KUP-11D55-12

 

[albertc30]

Okay, so my description won't work since I expected the switch to pass the motor current. You would need a relay with TWO sets of contacts. You would still use the circuit as described in post2, except the motor would be wired in series with the second contact and 12V. Sorry, I'm too lazy/busy right now to draw a schematic, but if you're having trouble visualizing it, ask. Any relay with a 12VDC coil, less than .5 A, and contacts rated for 5A or greater should work. For example (one of millions): TE Connectivity KUP-11D55-12

Ok.

For some reason I was thinking of relay as a step up/down like a transformer.

Just a few minutes before reading your reply it hit me the under floor heating with a I think 12V power supply. This was one of the few examples we had on our electrical on how to use a switch.

Then it hit me, one contact to get power from the battery to power the relay and one contact to get power straight from the battery and power the motor without having to go through the 0.5A floating switches.

By the way, what software do you use for drawing schematics please?

Any good free source out there?

Many thanks for your time.

Much appreciated.

Albert