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By bradfordgerl
Hey All,

I am attempting to take a waste tank that I have placed two float switches and a pump in (1 high switch and 1 low) and empty the tank automatically when the water level reaches the top float switch. Currently the float switches activate when they reach 45 deg. However if I just make a circuit this way the top switch will never activate and the bottom switch will always be running the pump. I know there is a way to use a switch/controller to handle the logic of making sure the bottom switch does not activate until the top switch has been set off. I am just needing help pinning down what type of logic switch or controller would accomplish this. Any direction or help on this would be appreciated!
User avatar
By DanV
First question - Don't your float switches each have 2 contacts? 1 Normally open and 1 normally closed?
If yes, then it's relatively simple to set up a circuit using a relay to latch the top switch normally open contact (and start the pump) along with the bottom switch normally closed contact used to break the latch (and stop the pump).

See this site - 4th diagram down from the top: ... s-r-latch/
By bradfordgerl
Both switches are normally open. So my plan would be to set up a circuit that would not allow the circuit to start the pump until both the top and bottom switches have been closed. Then I would like the circuit to continue to stay closed even after the top switch has become open. So basically I don't want the pump to stop pumping until all the liquid has been pumped out. Do you think that the s-r latch in that 4th diagram can do that? As I'm looking over the article I'm not sure that this will get the job done. I drew up a diagram of how our system looks, but I don't think this forum allows for pictures to be attached.
User avatar
By DanV
Well, I certainly don't know what I was thinking when I said bottom switch normally closed.
Of course it's normally open.
With high water level, both switches are closed, starts the sequence which runs until the bottom switch goes from held closed by the float to open which opens the latch circuit.

Your top switch is the Start switch in diagram #4 and your bottom switch is the Stop switch.

You are going to need a relay, of course.
By bradfordgerl
Yes the way you just explained it is exactly how it is setup and how I wish it to work. Do you happen to have a link to these switches. Cause theoretically I get what you are saying now, but actually finding this switch might be a challenge.
By bradfordgerl
DanV. So after reviewing your comments and looking over the 4th diagram it sounds like this could get the job done. Would you be able to point me in the right direction of where to purchase this circuit/Relay? I'm hoping there is a location near me that I could walk in and the employees would actually know what I am talking about. I don't really want to purchase online, but if I have to a will and just hope it works out. I live in Long Beach California if you happen to know somewhere in my area that would be a huge help.
By lyndon
Simplest way is to use a latching relay (or make a latching relay from a DPDT relay) that turns on when the upper float closes and turns off when the lower float opens. See ... y-circuit/

The "push to make" switch is your upper float and the "push to break" switch is your lower float. Good luck finding any store where the employees can still do this kind of stuff.
User avatar
By DanV
SparkFun has a 40 amp solid state SPST relay that would likely do your job nicely.
The only change to the diagram #4 is that your motor would be wired in parallel with the relay coil because there's only have one contact on that SS relay.
Have a look at this thread:
Now, there's some concern about when that relay fails it would fail in the ON state but that's likely true of a mechanical relay as well.
A 40 Amp relay has plenty of capacity to have a huge long life in this sort of application.
By teprojects1

Let me suggest you a simple and quick solution. I think you should use Arduino UNO along with 12V DC Pumps and you will also need relay driver to control those pumps. & will need 12V adapter as well. If you are interested in it then let me know and I can help you completely.

As the switches are concerned they are not that difficult to control with arduino.

By lyndon
You're not content to spam the groups, you also need to grossly overcomplicate a simple design? I'm all in favor of throwing microcontrollers every which way, but in this case, the entire solution can be done with a single DPDT relay or two SPDT relays.
By teprojects1
First of all I wasn't spamming the forum. Secondly, I have suggested a really good solution, he said that he wants some solution related to controller / switch control. So, I just presented an embedded solution.

The one you provided is good but not much flexible. Although, if you shake hands with embedded, then you can do anything. :P Peace :)
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