DIY ATO relay wiring question with illustration

Wetline

New member
I have never wired a relay before so I'm asking the experts how this diagram looks. If anyone spots a problem with the plan here please chime in, I'm not afraid to hear the wiring is completely wrong.


ATOwiringdiagram_zps4bac0a06.png


If you are going to say I should have just bought one, you are probably right but what's the fun in that and when it's all over this route may have saved me $5.00.

Relay:
http://www.radioshack.com/product/index.jsp?productId=2049722&filterName=Type&filterValue=DPDT

Switch:
http://www.radioshack.com/product/index.jsp?productId=3098835

Pump:
http://www.ebay.com/itm/Small-Dosing-Micro-Mini-12v-DC-Water-Pump-Hydroponics-W-Tubing-Power-Supply-/300738081640?pt=LH_DefaultDomain_0&hash=item460562f368

Float switches:
http://www.ebay.com/itm/330439881532?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

I do not have the power supply in front of me but I can post it up later if there are concerns about it.
 
It's completely wrong. :lol:

What's the switch supposed to be for? To let you "intervene" and turn the whole thing off during water changes or something?

The way you have it, there's never any power across the relay coil so it will never switch. You need to run 12v to one side of your series of float switches, then from the other side to one side of the coil. Then ground the other side of the coil. (the coil is pins 7 and 8 on the relay).

Run the ground from the pump directly back to the ground from the wall wart.

Run 12v from the wall wart through the switch, then to one of the poles for one half of the relay (say, pin 6). Then run pin 4 or pin 2 (depending on if the float switches are NO or NC) to the +12v terminal on the pump.

Leave the other switched circuit (pins 1, 3, and 5) totally alone.
 

Wetline

New member
It's completely wrong. :lol:
That's what I was afraid of! I'll make some revisions based on your instructions. Everything made complete sense except for the float switch circuit. Does the diagram below look like it should work?
Yes, the switch would be to kill power when I need to instead of digging through cords to find the plug.

ATOwiringdiagram_zps912ee1f2.png
 
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madean

New member
I say your schematic looks good. The one thing I would suggest is to test all your components with a voltmeter. A decent volt meter will have a continuity test mode on it. Check your switches and make sure they work the way you think they will work. So your float switches work the way they will work and hook them up in series like you have on your schematic. Do this with no power on the circuit. One way to check to see if the coil is good on the relay is to check resistance across the coil. From the diagram, it's looks like pins 7 and 8 are the coil. You should be able to touch one meter lead on one side and touch the other meter lead on the other side of the coil and read a resistive value on the meter in the resistive setting usually expressed in ohms. You should also read the contacts for continuity. Their should be a setting on the meter for that as well. Set the meter to continuity test and touch the leads together, the meter should beep continuously. Now you can touch you expected normally closed contact pins. Write this down to help you understand the relay. Once you have figured out which pins are the corresponding normally closed contacts you can energize the coil and see which contact pins close and give you continuity. These are the normally open contacts. In my line of work, a schematic is shown in a deenergized, depressurized, with no stored energy. Basically it's the state you would see the relay on the shelf of a store. So it will help you to understand what is going on here with this relay. You have contacts in the relay that are normally open and normally closed when the coil is deenergized. When you energize the coil the contacts flop state. So the contacts that are normally open will close, and the contacts that are normally closed will open. So it is important that you understand that by energizing the coil are you are doing is using contacts activated bay coil to provide a path for electricity to flow for your intended purpose. In this case you want to use two float switch (redundancy in case a float switch sticks in the open position) that will provide a path for electricity to flow to a relay coil. The idea is to have an energized wire lead to the first float switch. Once the first float switch is activated (water gets low) the second float also needs to duplicate the first switch. This allows power to get to the coil and change the states of the contacts. Thus providing a path to energize the pump to replenish evaporated water. When the water level reaches the float mark only one float needs to activate to interrupt the circuit that is energizing the coil on the relay. Once the coil is deenergized the contacts change state again and kill the path for the pump to operate. Thus turning off the pump. So make sure you understand your components. Also take a look at how your float switches are mounted. Remember you will have voltage from your switch labelled "acc" to the first float switch. So if this connection is inside the sump you will need to make it a water tight connection or figure out a way to have it wired outside the sump. If,when you loose power to the tank and a back siphon occurs, you could have water enter the sump and submerse this connection. And then when the power comes back on you can possibly energize the water in the sump and display tank and you have your hands in the tank at that moment you could shock yourself. We are only talking about 12 Vdc but still, you want to be careful in your setup. It probably would not be a bad idea to fuse in between your power supply and the power switch to protect your components. I hope this response has helped in some way. Good luck and please read, research how to make good electrical connections if you do not know how.
 
Does the diagram below look like it should work?

Yes but only if you orient the float switches such that they are closed when the water level is too low (I'm assuming you want one switch at the normal water level and the second above it as an emergency in case the lower switch sticks). The ebay auction you linked mentions that the orientation of the switches (NO or NC) is reversible by flipping them upside down, so you should be all set. If it doesn't work, flip them over. Luckily it's easy to test the whole thing by wiring it up on a workbench and just pushing the float switches open or closed by hand.

Also it may be obvious but it's good practice to cover any relay pins you're not using (pin two will have 12v on it whenever the topoff pump is not running, so you don't want it touching anything conductive).
 

madean

New member
Good points der wille- one last question, how long will your wiring be. Will the power supple, relay, pump and switches be located relatively close to each other or will they be far like on multiple levels of the house. The reason I ask is for a possible voltage drop issue. If they are close don't worry, but if they are far you might need to beef up the size of wire you use for this circuit.
 

Wetline

New member
Thank you both for helping out a electrical noob! The wiring will only be a few feet long so voltage drop due to distance shouldn't be an issue.

I will play with the voltmeter and make sure the power is flowing through the relay as it should. The float switches hadn't arrived yet as of yesterday afternoon so I haven't given it a complete test run yet. I should have everything soldered/crimped up and get it operational this weekend.

Thank you both again!
 

madean

New member
Uncle where would a good place to get these parts and what are the parts in this diagram? Maybe a list of parts will help others in the long run :-D
 
It's more or less the same parts as we're already discussing, except no lit toggle switch and it's assumed the pump is 120V AC instead of 12v DC. It is definitely a different circuit with a different function though.

I would be interested in discussing the "most time tested and reliable" comment, but I'm pretty sure uncle has me ignored because he never responds directly to my posts. The diagram uncle posted shows a latching circuit, where a low level switch toggles the pump on, and a high level switch toggles it off. In this design, you essentially have a single point of failure in that if the high level switch sticks, the ATO will run happily forever. In the non-latching design we were discussing earlier in the thread, there is no latching (a single switch toggles it on AND off), and the second float switch is set higher than the desired water level, which means if the primary switch sticks, the second switch will turn the pump off before things get ugly.

Redundancy aside, to a certain extent latching vs. not is personal preference or at least dependent on the exact functionality you want. The latching circuit allows you to choose how much water evaporates before the ATO kicks on (by controlling the difference in height between the two switches) while the non-latching design we were discussing earlier does not (the amount of evap that occurs before the ATO kicks on is determined by the amount of throw in the switch). To me, this isn't a huge issue, as I find it desirable to have a very small variance, since that means salinity will fluctuate less.

The only other difference is the inclusion of a flyback diode (D1) which snubs the current when the coil in the relay switches off. This would be nice to have but IME isn't a strict requirement as the float switches have a pretty vast capacity compared to what's in the circuit.
 

madean

New member
wetline, I just looked at that relay and you should be able to get a base for it to plug into. The base then has termination points where you can just lug the wire and not have to solder. These base plates can then be mounted how ever you like. That way if and when the relay coil burns up you just pull out the coil and replace it with a new coil.
 

Wetline

New member
wetline, I just looked at that relay and you should be able to get a base for it to plug into. The base then has termination points where you can just lug the wire and not have to solder. These base plates can then be mounted how ever you like. That way if and when the relay coil burns up you just pull out the coil and replace it with a new coil.

Yes but that costs more $. I just opted for crimp-able quick connect fittings. I'll have to solder a few things but not to the relay. I'll use something like these.
http://www.radioshack.com/product/index.jsp?productId=2104018

I also got a project box from radioshack to pull the bird's nest of wires and the relay in.

Also, if anyone decides they want to do something similar there are cheaper options on ebay for float switches, pumps, and relays but I didn't want to wait for everything to come from China so I only bought Chinese products from North American sellers :lol:.

Thanks again for all the input everyone. I wasn't able to find a good diagram of a relay wired correctly for an ATO. With help from der_wille_zur_macht and everyone else there's now a few illustrations out there for people to review if they decide to do something similar.

Big fan of all of beananimal's DIY stuff but I don't really see how his is all that much better of a design than basically every other two switch system. I went on his site looking for a write up but didn't see a specific page for his ATO. Again, he knows what he's doing and I'm sure he had his reasons but for me I'll stick with the original (revised) plan.
 
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Kawi9_cf

New member
That's what I was afraid of! I'll make some revisions based on your instructions. Everything made complete sense except for the float switch circuit. Does the diagram below look like it should work?
Yes, the switch would be to kill power when I need to instead of digging through cords to find the plug.

ATOwiringdiagram_zps912ee1f2.png


Maybe I am looking at this wrong but if you are going to be using a 12v DC pump why even use a relay? The float switches can safely and easily switch on and off a 12V pump.
 

madean

New member
Kwai 9 does have a point. Usually the pump is ac and not the same dc voltage. I can't believe 3 of us did not catch that. Lol
 
I would not change the design. These cheapo little float switches are very fragile. I wouldn't want it directly switching a load as big as even a small pump. The coil in the relay will draw less power and prolong the life of the switches.
 

Kawi9_cf

New member
The switches are rated for 500mA and 10 Watts. The pump is only a 250mA 3 watt pump I believe you will be just fine without a relay for that particular pump.
 
I understand that on paper the switches are rated higher than the pump's requirements, but personally I would still use the relay. I don't like running wimpy reed switches with any more than the bare minimum current I can get away with. Despite the ratings, I've seen plenty of them with the contacts fused shut. To each his own though.
 
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