AC relays, outlets, and switches oh my!

Discussion in 'The Projects Forum' started by the_jaydog, Oct 14, 2008.

  1. the_jaydog

    Thread Starter New Member

    Oct 9, 2008
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    Hello everyone. This is my first post, and I hope someone can help before I lose all of my hair! I have a saltwater aquarium and it has a sump underneath it. It drains water from the display tank above, goes through a few things that realy don't matter, and the water returns to the display tank via a pump. My problem is this, water evaporates pretty quickly. The normal solution to this problem is take an extention cord, split and cut one of the two wires(midway), and connect a float valve to the two leads. Then plug a power head into the outlets on the end of the extention cord. The idea is, when the float drops down, the circuit completes, turning the pump on, the pump draws water from a storage container and puts it into the sump until the float goes up, cutting the circuit off, and killing the pump.

    A second problem is that the pump needs to be off when feeding the fish. I would always unplug the pump, feed the fish, when they ate all the food, I would plug it back in. She hates this idea!

    I do have to agree with her, a little. I do think this is very ghetto! My wife is already pretty irritated that we have to have to have all the plumbing and other crap just for a few cool looking fish. She calls it my "science experiment". I would realy like to have a nice, neat, sophisticated looking something or other to make her happy, but still something that looks cool to impress my friends.

    My ultimate plan is to use a plain old Radio Shack project box that houses a switch, to turn the whole circuit on and off, maybe with a few lights to tell me if the pump is on and off, then go through to a single outlet where the pump plugs in, then through a relay or two, (however many I might need) then through two float switchs about three or four inches away from eachother, (verticaly). When the water drops below the bottom one, it will kick the pump on, (plugged into the bottom outlet) and the pump will run until the top switch turns the pump off. I need the switch to shut everything down so she can flip it, feed the fish, and flip it back on a few minutes later.

    I tried to do this using a 125V switch from Radio Shack, then an outlet, the to through one float switch, then to another outlet. The first outlet for the sump pump, the second for the new water pump. This didn't work at all. For some reason the first outlet tested at like 30VAC the second tested at around 90VAC I know I did something wrong. I have seen where people have made similar set-ups using 12V relays. I thought that 125VAC relays would save on confusion. I know I could easly be wrong. I hope someone could help me. I'm afraid my wife is going to get rid of me and the aquarium both. Please help me! Thank you all very much for any help you can provide.
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    An inverted coke bottle to replace the water? Sorry, couldn't help myself.

    I will say this, high voltages and water don't mix.
     
  3. hobbyist

    Distinguished Member

    Aug 10, 2008
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    There is a very safe way to do this, first keep your pump on it's own seperate circuit, don't mix it's line voltage in direct contact with a float valve.

    Use a relay to switch your pump on with. Put the float valve on a transistor relay driver circuit.

    Float valve connects a small signal voltage to a transistor and the transistor switchs the high voltage relay to run the pump.

    That way all water related items are on the low voltage (dc) side of the circuit.
     
  4. the_jaydog

    Thread Starter New Member

    Oct 9, 2008
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    After googling "transistor relay driver circuit" I tink I'm only mre confused than before. I normaly understand things better in the form of a picture. This is probably the reason I did such a poor job explaining myself in the thread. I hate to ask, but would you mind giving a picture? Thank you so much for you help!
     
  5. hobbyist

    Distinguished Member

    Aug 10, 2008
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    Hi
    I am not a licensed electrician so the circuit on the mains side can be up for scrutinizing by someone more knowledgeable, but the DC side works like this.

    The float can trip a switch that makes a somplete circuit to the Base of the transistor through its limiting resistor, this in turn alows DC electron current to flow from the neg. side of a DC supply (battery or linear supply)
    through the transistor into the coil of the relay energizing the relay coil to close the contacts on the mains circuit where the pump runs on.
     
  6. the_jaydog

    Thread Starter New Member

    Oct 9, 2008
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    0
    Okay I see what you're saying now. After seeing your drawing, it gave me an idea. I know that their are several things in my drawing that need to be solved. Hopefully you can help. I guess I could use one float switch but I was afraid it would kick off and on to many times and wear out prematuraly. I was thinking that by using two float switches it would only need to top off maybe once every two days or so, obviously depending on how far away I placed them.

    I thought I could get away with using one relay, radio shack part# 275-0217, because it apeared to have two sides. I now understand the relay better, and realize that this isn't the case.

    I really like the idea of using a 12VDC on the switches. I could have probably messed something up real good if you had not recommended it. Thank you!

    In my drawing you can see that I was confused about where to connect the 120VAC. I know that the relay system, and floats are suppose to "interupt" the current, but I am pretty sure I'm wrong on my connections in the pair of relays. Would you mind taking a look and seeing if you could straighten them out for me? I don't even know if this setup is possible. I really hope so though. This aquarium demands so much attention, I would love to not have to worry about one more thing. I could pay a lot of money, and buy a cheap, unreliable system, that still wouldn't do what I wanted, but why? I like trying to figure this stuff out. I'm just glad their are smart people like you guys to help out when the going gets tough.
     
  7. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
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    Hi
    I'm going to try to come up with something that might be one way of doing this, I can see what your saying about one switch causing the pump to come on everytime the water drops that would cause a lot of on off conditions. I'm going to draw up a pictorial and schematic drawing of a SCR circuit that will work by 2 limit switchs, and would turn the pump on at a certain level and off at a certain level.
     
  8. hobbyist

    Distinguished Member

    Aug 10, 2008
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    Hi.
    See if this helps out.

    Whoops!!!! the SCR is hooked up wrong the relay coil needs to go from ground to the SCR. Sorry about that...

    This is just to give you an idea and try to point you in the right direction, read up on SCR's they are very handy for applications like this, they act like electronic relays.

    The whole idea with using an SCR is that the pump will not go off and on every time the water starts to drop but rather by setting the collars on the float rod you can determine when to turn the pump on and off.
     
    Last edited: Oct 17, 2008
  9. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
    56
    Hi.
    This is the schematic corrected
    The coil of the relay goes from ground to the cathode of the SCR.

    The SCR acts like a electronic switch, that comes on and stays on until you turn it off with another switch input.
    This eleminates the pump from turning off and on every time the water causes the switch to bounce on and off.
     
  10. raybo

    Member

    Oct 18, 2008
    22
    0
    why electronics when you don't realy need put the water higher then the container then a simple spigot will work just like for my dog water contatiner 1 gallon when he drinks the water will replenish automatically. go to pet store buy the the damn thing is cheaper then all this control and plunbing. scientist.
     
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