Dual float switch

[kwame]

Hi There!
I have been tasked by my boss to use two tethered float switches having three leads to control a basement sump pump. He claims one needs to be placed halfway ,with the other at the bottom of the well.I am having a hard time designing a simple circuit to control the pump,using a 3phase contactor.The object of using two switches is to prevent pump from fluttering ON/OFF every second.

 

[Ramussons]

Something like this?

 

[Les Jones]

Hi kwame,
If you think about a motor starter with a stop and start button then the switch at the bottom of the sump needs to trigger the stop button. (A contact that opens when the water level is below the switch connected in series with the stop button.) and the switch half way up the sump would trigger the start button. (A contact that closes when the water is above the switch connected in parallel with the start button.) Now some questions. Question 1 Is the control circuit going to operate at mains voltage or some low voltage (12 or 24 volts.) Question 2 Is the three phase contactor controlling a three phase supply or are you just using one or two sets of contacts to control a single phase supply. If it is controlling a three phase supply does it have a spare set of normally open contacts. This is to know it can be made to latch on.) Question 3 what is the mains voltage. Say weather this is phase to phase or phase to neutral. What is the coil voltage on the contactor ?

Les.

 

[kwame]

Hi Les
I think you have posed very relevant questions.I think you want me to use a circuit similar to DOL motor starter;just shortly before i read your reply,i was considering a similar picture.The control circuit is going to be lines voltage-240VAC(contactor coil) and the motor/pump is a three phase one.The contactor has no spare NO contacts so may be ,we have to use an auxiliary NO contact.

 

[Les Jones]

Hi kwame,
You could use a small relay with a 240 volt AC coil connected in parallel with the contactor coil and contacts rated to take the current required for the contactor coil. The contacts on the small relay would be connected in place of the auxiliary contacts on Ramussons diagram.

Les.

 

[MikeMl]

Something like this?

View attachment 93354

Isn't the float switch logic backwards? You want to latch the contactor on its own aux contact when the water reaches the mid float, so that switch would close when the water level rises above it.

The pump is supposed to run until the water level drops to the bottom float switch, so it would have to be wired so that its contact is closed when the water is above that switch, and that would unlatch the contactor.

I think you should use a contactor with a 24Vac coil and a control transformer, so that everything on the water side is low-voltage...

 

[Ramussons]

Ok, I thought that the idea was to fill a tank halfway.

If the idea is to empty the tank, just view the schematic up side down

ps interchange the names of the floats.

 

[Les Jones]

MikeMl, I agree.

Edit
Ramussons, If you interchange the floats switches you would still need to change the sense of the switching on the mid level switch (Now at the bottom of your diagram) so it was closed when the water is above the switch level.

Les.

 

[kwame]

Hi Mike
The objective is to empty the sump well.Plaudits everybody for sugestions:Les,MikeMI,Ramussons.

 

[Reloadron]

Kwame, I would use a latching contactor and as Mike suggest a 26 VAC circuit, something along these lines:

Your float switches have a Common, Normally Open and Normally Closed. The Lower Switch uses the N/C contact so it will be closed unless the water level drops below it. When the water level reaches the Upper Switch which is N/O it will close and K1 the motor contactor will pull in, the K1 Aux N/O contacts will latch K1. The pump will run till the sump is empty and the water level drops below the lower switch. Make sense?

Normally your pump will be protected I have not included thermal overload or the 3 phase power. Make sure the contactor is rated for the horsepower load of the motor.

Ron

 

[kwame]

Ron, makes a lot of sense.So long, what have you been up to?

 

[Diver300]

Reloadron's circuit should work, but there is a slight issue with the naming of the switch connections.

I assume that both float switches are identical. To keep the water between the level of the two switches, both switches need to close when the water gets to the float.

Water is below both switches, both are open and the pump stops.
Water is above the lower one, so the lower switch is closed. Pump may be running, or it may not, depending on whether the water was most recently high or low.
Water is above both switches, so both are closed and the pump starts.

So as both switches need to function in the same direction, I would expect them both to be wired to terminals labelled the same on the two switches. In this case, I would expect to wire to COM and N/O, which are likely to be the ones that close when water gets to the float.

N/O stands for "Normally Open", and the term might be a bit confusing in this situation, because the water level will normally be between the two switches, leaving one submerged all the time, so the "normal" condition for that one is to be operated. Reloadron's circuit shows the correct terminals for start and stop pushbuttons, where you don't get someone pressing the button for most of the time, so the start button is normally open and the stop button is normally closed.

 

[MikeMl]

You notice that I avoided reference to the NO-C-NC labeling embossed on the physical float switch, and described the float switches in terms of what the water level is actually doing...

I've been tripped up on this issue before...

 

[kwame]

The float switches only will cycle pump ON/OFF without push buttons. Both need to close in tandem to comlete circuit and activate pump when water level reaches upper switch . When water level drops below upper switch,its N/O contacts will open but;pump will be working as lower switch will sealed it.The pump will work till water falls below lower.If lower switch NC ontact is used it won't work as will be opened when water level reaches upper switch circuit will. be incomplete. Ron's brief needs a relook
Kwame
Ghana

 

[Les Jones]

You just need to use the NO contact on the lower switch instead of the NC contact.

Les.

 

[kwame]

My draft circuit is in line with that of Diver300 and LES. The sump is to be used at the lower(-2)basement of 24 storey luxury apartment block prone to flooding. You can see the building by typing the word 'villagio' apartment s at google.It is the building clad in yellow .It is tallest building in my country with sky-deck swimming pool at rooftops,lifts etc or visit **broken link removed**

 

[Reloadron]

My draft circuit is in line with that of Diver300 and LES. The sump is to be used at the lower(-2)basement of 24 storey luxury apartment block prone to flooding. You can see the building by typing the word 'villagio' apartment s at google.It is the building clad in yellow .It is tallest building in my country with sky-deck swimming pool at rooftops,lifts etc or visit **broken link removed**

Ron, makes a lot of sense.So long, what have you been up to?

Me? Been enjoying my summer and retirement. Funny about the sump of water. In a few days we head to New York City and where I grew up. I go back every year about this time to see old friends and we have a party on the beach. Last year we watched the morning news and they were talking about flooding in Cleveland, Ohio where we live now. Then the camera showed the corner of our street underwater. Called my neighbor and we are on the high ground, he checked and we were dry but many neighbors lost plenty. Last time I replaced our sump pump I went with a much larger than needed 1 HP unit. Glad I did and we also have an emergency generator with auto transfer. It was so strange being in NY and seeing our street corner on TV.

The drawing I did, I should have omitted the common, n/o and n/c. Knew that might bite me. Something I would consider is a high water alarm in case of pump failure. That drawing was done rather quickly and I had to modify the parts. You may also want to add a simple push button so the pump can be cycled before it would automatically turn on.

Ron

 

[kwame]

May be we will add a push button. It is sunday morning 10:28am here but.Iam at work ; we doing some minor work at the underground Substation. I come to work on sunday to make ends meet. I earn around (USD)150$ monthly including sunday's wages.The villagio apartment are built by an. Italian Owned firm named Trassaco. They use the cheap labor here