Float switch wiring help
#1
12-28-03, 07:21 PM
Float switch wiring help
I'm want to use float switchs to have an auto top-off system for my aquarium. Electricity is not my strong point so i'm looking to you all for some help.
I am going to have 2 float switches, 1 will be the main switch and the other will be a back up switch. When the water level drops it will complete the circuit and activate a small pump to add water, when the water level is back to were it should be, the switch will open and stop the pump. If that switch fails, the next switch should open when the water level gets to high and open the circuit and shut off the pump. That's the easy part.
But I don't want 120v operating the float switch. If anything were to go haywire, I don't want the electricity to wipe out my aquarium, that would suck BIG TIME!!
I have read were people will use a relay or something to provide 12v to operate the float switch, but can still provide the 120v to the pump. Does this make sense?
So I need to know where to find a relay for my needs and how to wire this whole thing together. I have found a bunch of relays, just don't know what would work for my application.
Any info I can provide to get this figured out, let me know.
Thanks
I am going to have 2 float switches, 1 will be the main switch and the other will be a back up switch. When the water level drops it will complete the circuit and activate a small pump to add water, when the water level is back to were it should be, the switch will open and stop the pump. If that switch fails, the next switch should open when the water level gets to high and open the circuit and shut off the pump. That's the easy part.
But I don't want 120v operating the float switch. If anything were to go haywire, I don't want the electricity to wipe out my aquarium, that would suck BIG TIME!!
I have read were people will use a relay or something to provide 12v to operate the float switch, but can still provide the 120v to the pump. Does this make sense?
So I need to know where to find a relay for my needs and how to wire this whole thing together. I have found a bunch of relays, just don't know what would work for my application.
Any info I can provide to get this figured out, let me know.
Thanks
#3
12-28-03, 07:44 PM
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How would you know whether the first float switch has failed. Sounds to me like you need another couple of sensors to sense overfill/underfill conditions.
If I were designing this I would consider designing a low voltage logic circuit to process the inputs from the sensors and the float switches and then operate the pump as needed. You can easily put together some simple logic with the standard 74 series chips. They usually run on 5V. TTL or HCMOS should work fine.
You can use a transformer to convert to 5V/12V as needed for your circuit.
If I were designing this I would consider designing a low voltage logic circuit to process the inputs from the sensors and the float switches and then operate the pump as needed. You can easily put together some simple logic with the standard 74 series chips. They usually run on 5V. TTL or HCMOS should work fine.
You can use a transformer to convert to 5V/12V as needed for your circuit.
#4
12-28-03, 07:45 PM
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With those ratings all you'll be able to switch is a relay coil.
That is one light duty float switch.
This project will have to be makeshift. I don't know of anything you can just apply to this setup. You will be wiring it from scratch.
That is one light duty float switch.
This project will have to be makeshift. I don't know of anything you can just apply to this setup. You will be wiring it from scratch.
#5
12-28-03, 09:28 PM
Here is a drawing of the way I was going to do it. But this way, all 120v will be going to the switch. I can't have that. If for whatever reason that switch leaks 120v into the water, my tank is wiped out.
I was told by some other folks that I can use a 12vdc Dpdt relay in there so it would only use 12v to activate the switch, but still send 120v to activate the pump. Would this work? If so, how would I wire it in?
The pump I would be using is a 20v pump.
Hopefully I can attach this drawing. It was done in MSPaint and saved as a jpeg.
I was told by some other folks that I can use a 12vdc Dpdt relay in there so it would only use 12v to activate the switch, but still send 120v to activate the pump. Would this work? If so, how would I wire it in?
The pump I would be using is a 20v pump.
Hopefully I can attach this drawing. It was done in MSPaint and saved as a jpeg.
#6
12-28-03, 09:35 PM
Ok, guess I can't attach it. Let me explain the wiring I have so far:
Take an extension cord and cut one wire. Take one wire from switch and attach to the male side of the cut. Then take the other wire and attach to a 'jumper' wire. Take the other switch and attach one wire to the 'jumper' wire at the opposite end and put the final wire to the other cut end of the extension cord.
The first swith wired in will be 'NO' (main switch)and the other will be 'NC' (back-up switch).
But I need to get a relay in there somewhere.
Take an extension cord and cut one wire. Take one wire from switch and attach to the male side of the cut. Then take the other wire and attach to a 'jumper' wire. Take the other switch and attach one wire to the 'jumper' wire at the opposite end and put the final wire to the other cut end of the extension cord.
The first swith wired in will be 'NO' (main switch)and the other will be 'NC' (back-up switch).
But I need to get a relay in there somewhere.
#12
12-28-03, 10:57 PM
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1. For the two switch scheme to work they need to be connected in parallel - not in series. If the first switch sticks open there is no way the second switch is going to close the circuit. It will work if the switch sticks closed. I don't know anything about these switches but I would imagine then can stick either way.
2. The parallel scheme may also have hysteresis problems. Both float switches will not open and close at the same instant so you may have the problem of the motor starting and stopping before settling - intermittent behaviour. You can live with it but is not good design practice.
3. The low voltage issue also needs to be addressed., You will need to include a low voltage power supply to address this.
I would recommend what I said in my first post. If you are not familiar with logic design I'm sure you can get some simple books on the subject. Try somewhere like Radio Shack or Fry's (not sure if they exist outside CA). Since the design is simple I'll be happy to reduce the logic and give you a simple gate diagram for implementation. For exmaple intermittent behaviour can be prevented with proper debouncing or a schmitt trigger.
2. The parallel scheme may also have hysteresis problems. Both float switches will not open and close at the same instant so you may have the problem of the motor starting and stopping before settling - intermittent behaviour. You can live with it but is not good design practice.
3. The low voltage issue also needs to be addressed., You will need to include a low voltage power supply to address this.
I would recommend what I said in my first post. If you are not familiar with logic design I'm sure you can get some simple books on the subject. Try somewhere like Radio Shack or Fry's (not sure if they exist outside CA). Since the design is simple I'll be happy to reduce the logic and give you a simple gate diagram for implementation. For exmaple intermittent behaviour can be prevented with proper debouncing or a schmitt trigger.
Last edited by rav12; 12-28-03 at 11:14 PM.
#13
12-28-03, 11:31 PM
1.) The way I understood the 2 switchs in a series would be this:
The lower switch will not activate the pump untill the water level drops, then when the pump fills the water back up, the switch will shut off the pump.
The second switch mounted higher would only come into play if the 1st switch gets stuck leaving the pump on and continues to fill, untill it trips the 2nd switch, which would break the circuit and turn off the pump. Basically a back-up.
2.) There for, both switchs won't have to operate like you had suggested.
3.) A 12v power supply would be needed, yes.
Would the relay work then, provided it is suited to work with the float switch rates and the pump voltage?
A gate diagram would be great.
Thanks, and if you can post that for me here, that would be cool. Don't know why it would'nt attach for me.
The lower switch will not activate the pump untill the water level drops, then when the pump fills the water back up, the switch will shut off the pump.
The second switch mounted higher would only come into play if the 1st switch gets stuck leaving the pump on and continues to fill, untill it trips the 2nd switch, which would break the circuit and turn off the pump. Basically a back-up.
2.) There for, both switchs won't have to operate like you had suggested.
3.) A 12v power supply would be needed, yes.
Would the relay work then, provided it is suited to work with the float switch rates and the pump voltage?
A gate diagram would be great.
Thanks, and if you can post that for me here, that would be cool. Don't know why it would'nt attach for me.
#14
12-28-03, 11:52 PM
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1. In this case, yes it should work OK.
2. Intermittent operation can still occur. Any ripples or waves on the water can cause the switches to bounce up and down before settling.
3. To use a relay you will need to design a step down power supply and then connect the float switches on the low voltage side and use this to switch the relay. To use standard logic gates you will typically have to work with 5V - not 12V. With proper logic the switches do not necessarily have to be connected to each other - the logic will process the info. I will knock up the basis for implementation when I have more time in the next few days but I'll leave it to you to fill in some of the details.
2. Intermittent operation can still occur. Any ripples or waves on the water can cause the switches to bounce up and down before settling.
3. To use a relay you will need to design a step down power supply and then connect the float switches on the low voltage side and use this to switch the relay. To use standard logic gates you will typically have to work with 5V - not 12V. With proper logic the switches do not necessarily have to be connected to each other - the logic will process the info. I will knock up the basis for implementation when I have more time in the next few days but I'll leave it to you to fill in some of the details.
#15
12-29-03, 01:13 AM
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#17
12-29-03, 08:35 AM
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You cannot access the page by clicking on the link. But you can by copying the URL out of rav12's post and pasting it into your browser.
#18
12-29-03, 09:05 AM
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Clicking on the link works for me - both in Netscape and IE. It could be a browser setting that could be preventing this. Most times a browser only reads an HTML page that has a JPEG embedded in it. The link points to a JPEG file so this could be causing the problem.
If you still have problems I will email it to you.
If you still have problems I will email it to you.
#20
12-30-03, 06:13 PM
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Feel free to send me your circuit when you're done - I'll be happy to check for any obvious problems.
Regarding building the project - you should get yourself a soldering iron and some circuit prototyping board for the "brains" or logic parts of the circuit. Most hobby electronics stores can sell you the stuff you will need.
Regarding building the project - you should get yourself a soldering iron and some circuit prototyping board for the "brains" or logic parts of the circuit. Most hobby electronics stores can sell you the stuff you will need.
#22
12-30-03, 06:48 PM
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I see you've decided to skip the logic part of the design. Yes, this should work as far as I can see. The only thing is that the relay connection on the mains side looks more complicated than it needs to be.
You need to simply connect the relay in series with the hot wire. So you have the hot wire going in to one contact on the secodary side of the relay. You the take the hot output from the other contact on the relay and feed it to the pump. The return from the pump does not have to go to the relay since the relay only has to interrupt the hot side to break or make the circuit.
You need to simply connect the relay in series with the hot wire. So you have the hot wire going in to one contact on the secodary side of the relay. You the take the hot output from the other contact on the relay and feed it to the pump. The return from the pump does not have to go to the relay since the relay only has to interrupt the hot side to break or make the circuit.
#23
12-31-03, 09:55 AM
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Check out your local Marine (Boat) store. They maybe able to help
as they carry all types of Float Switches and high-water alarm components which you may be able to adapt. If its not on the shelf ask to see thier catelogues of what they can get.
Best of all, the bilge systems are generally 12 volt. You can by a 12 volt adapter almost anywhere, Radioshack etc. It may come with a femal cigaret plug but you can cut that off.
Also I'm wondering if check valves may be able to help you, your thinking electrical, thier could be a mechanical answer.
as they carry all types of Float Switches and high-water alarm components which you may be able to adapt. If its not on the shelf ask to see thier catelogues of what they can get.
Best of all, the bilge systems are generally 12 volt. You can by a 12 volt adapter almost anywhere, Radioshack etc. It may come with a femal cigaret plug but you can cut that off.
Also I'm wondering if check valves may be able to help you, your thinking electrical, thier could be a mechanical answer.
#24
12-31-03, 10:36 AM
Thanks everyone for you help and ideas.
I wanted to keep this very simple. And the way I have it set-up should work just fine. There were several different ways but wanted to do it cheaply. And this way was pretty cheap.
I could of done it cheaper by doing a gravity type of set-up, but there would have been alot more work involed in the long run doing it that way.
I could of gone the dosing pump route, but those are too expensive. They work great, no doubt about that but didn't want to spend the cash.
I could have bought a system made specifically for what I want and paid over $100 for it, this way cost about half that.
I should be getting the float switches by the weekend. I'll do a test run and report back how it goes. Should work though.
Thanks again.
I wanted to keep this very simple. And the way I have it set-up should work just fine. There were several different ways but wanted to do it cheaply. And this way was pretty cheap.
I could of done it cheaper by doing a gravity type of set-up, but there would have been alot more work involed in the long run doing it that way.
I could of gone the dosing pump route, but those are too expensive. They work great, no doubt about that but didn't want to spend the cash.
I could have bought a system made specifically for what I want and paid over $100 for it, this way cost about half that.
I should be getting the float switches by the weekend. I'll do a test run and report back how it goes. Should work though.
Thanks again.
#25
12-31-03, 11:09 AM
Not sure what you finally came up with, but here is how I would wire your application:
Connect your 120V power source to a transformer to provide desired voltage for control circuit. Run one side of your low voltage from transformer (we'll call it the "hot" wire) through the two float switches (in series) to a simple relay with a coil matching the voltage of your control circuit and a set of normally open contacts rated for 120 volts. The other side of the coil is connected to the other side of the transformer. The hot wire of your 120V circuit not only goes to your control transformer, but also passes through the set of normally open contacts to your water pump. The control circuit "hot" wire runs through your float switches as follows: It runs to one side of a "hi-limit" float switch with normally closed contacts. In it's normal state - above the water - the contacts are closed and will always allow voltage to pass through unless the water rises high enough to change the condition of the contacts. The wire runs from the other side of the hi-limit switch to one side of the "fill" float switch. It should have normally open contacts - when the proper amount of water is in the tank. Whenever the water level drops, the contacts close and voltage will be sent from the other side of the fill switch to the coil. When the coil is energized, the 120V contacts close and allow the pump to come on.
You will need a 120V / xV transformer, two float switches (one with normally closed contacts, one normally open), and a relay as described above.
Connect your 120V power source to a transformer to provide desired voltage for control circuit. Run one side of your low voltage from transformer (we'll call it the "hot" wire) through the two float switches (in series) to a simple relay with a coil matching the voltage of your control circuit and a set of normally open contacts rated for 120 volts. The other side of the coil is connected to the other side of the transformer. The hot wire of your 120V circuit not only goes to your control transformer, but also passes through the set of normally open contacts to your water pump. The control circuit "hot" wire runs through your float switches as follows: It runs to one side of a "hi-limit" float switch with normally closed contacts. In it's normal state - above the water - the contacts are closed and will always allow voltage to pass through unless the water rises high enough to change the condition of the contacts. The wire runs from the other side of the hi-limit switch to one side of the "fill" float switch. It should have normally open contacts - when the proper amount of water is in the tank. Whenever the water level drops, the contacts close and voltage will be sent from the other side of the fill switch to the coil. When the coil is energized, the 120V contacts close and allow the pump to come on.
You will need a 120V / xV transformer, two float switches (one with normally closed contacts, one normally open), and a relay as described above.
#26
01-01-04, 07:54 PM
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Just a technical point - in effect by connecting the switches in series you have implemented the "AND" function. In digital circuit design jargon this is known as a "wire AND" circuit - in other words the logic was implemented without any special logic gates but by simple wiring. Many simpler designs can be used to wire such logic although it is very rarely used to design the circuits inside digital/processor chips due to the much higher degree of complexity. However, one place it is used frequently is at the outputs of chips when many parallel transistors are used to drive a common load.
#27
01-02-04, 06:15 AM
The circuit I outlined is an electrical circuit, not an electronic one. It is a simple "3-wire" control circuit and is one of the most common and simple control circuits found. There may be a different (and better) way to design the required function using electronic components, but most "electricians" on this board are more familiar with electrical components than they are circuit boards. And yes, the circuit uses "and" logic but that is by design. Both switches have to be in their proper state for the tank to fill properly. As long as the second switch in the series works properly, the first switch will never change state. Only if there is a malfunction in the second switch will the first switch be required.
#28
01-02-04, 11:00 AM
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I was refering to ereefic's circuit and just made the point given my original suggested implementation. In many ways his and your suggested circuits are similar.
There really is not a huge difference in designing logic circuits for electrical or electronic type situations. The only main difference I can think of are more formal methods of doing things for IC design since many ICs these days can contain millions of gates. In this case the problem can be solved by just thinking it out.
There really is not a huge difference in designing logic circuits for electrical or electronic type situations. The only main difference I can think of are more formal methods of doing things for IC design since many ICs these days can contain millions of gates. In this case the problem can be solved by just thinking it out.
