DIY auto shut off - The Planted Tank Forum
 
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post #1 of 10 (permalink) Old 07-21-2018, 01:21 AM Thread Starter
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DIY auto shut off

Help. Technically new to forum (just registered) but have been reading for a while.
I'm new to auto shut off switches triggered by floats.
I built a sump and I want to use a 2', 3 plug extension cord. I want the power to that cord to be shut off automatically if the water level goes too high OR too low. I was planning to build a quad float switch. 2 float switches for high water level and 2 float switches for low water level. Basically having a backup float switch for each side. I plan to have a heater, return pump, and light plugged into the cord.
I don't know how to match power ratings for double or quad pole relays in order to kill 110v/ac power from the wall based on float switches. I have 4 float switches that is like to use as well as the pump. I will post the photos of them when I bought them but I have not found a relay yet due to the power match issue.
Any help would be appreciated.
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post #2 of 10 (permalink) Old 07-22-2018, 07:51 AM Thread Starter
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Nobody on here does this?
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post #3 of 10 (permalink) Old 07-25-2018, 12:46 AM Thread Starter
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I guess I'm a loaner....
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post #4 of 10 (permalink) Old 07-25-2018, 03:25 PM
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Hi there

I would suggest a 12v control circuit to prevent yourself or your fish from being electricuted. So a 12v relay and an external 12v power supply will be needed. 1 Relay for HIGH and 1 for LOW. you can connect the two floats in series for this.

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post #5 of 10 (permalink) Old 07-31-2018, 02:43 PM
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I'm a bit uncertain about the question. How do you mean "match the power ratings"? Basic is that the voltage has to be the same at all points. Do you ask what each item's current rating should be? For that point, each item, like float switch has to be rated to handle more current than expected. A rating of 15 amp is quite common for 110AC but we rarely expect to use that much.
So the specs on the float switch say the max voltage can be as high as 220 AC but we will likely use lower. The max amount of current through the float switch contacts is rated at .5 amp. That leaves you to add up how much each item will be needing for current flow and make sure the total doesn't exceed that .5 limit.
There are online converters to help with the figures, so convert each item to from watts or however the info is listed, into watts or amps and then add them up.
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post #6 of 10 (permalink) Old 07-31-2018, 07:32 PM Thread Starter
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There is a way to use the relay posted below to kill power. Basically since I want to use a small extension cord with 3 plugs in it, I would splice into the hot wire and essentially put the relay in the hot wire. Hot wire----■----hot wire . Then the float switch would come off of the other side of the relay and essentially make or break the circuit. There are many different power levels of these relays and idk which to buy.
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post #7 of 10 (permalink) Old 07-31-2018, 08:50 PM
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Okay! Got a better idea of the problem.
For choosing the relay, there will be two different sets of ratings to look at before choosing which works best. The relay will have two items, the coil or part which makes the relay move and the contacts which act as the switch for the other equipment.
For the coil, we want to have it work at the same voltage as you are feeding the coil. If using 110 AC, get a coil that works at that range but they will often be rated much wider like from 50 to 200 volts. Just get somewhere between the high and low rating or one that says 110AC .
For the contacts that actually make/break the circuit it is controlling, get the same idea for voltage as before and then make sure the contacts are rated higher than the expected load total. So add up the current used by all the equipment controlled by the relay.
Example:
heater 200 watt, light 150 watt and pump at .5 amp?
Go to a converter online to convert the amps to watts or watts to amps, depending on how the relay is rated and then find a relay that can handle more than that amount of current. The point is that all the ratings make come up as different ways of saying much the same (watt, amp, horsepower, so we need to convert them all to the same unit of measurement) Not technically the same but close enough for what we do on this. Point is to be sure to have a relay that can handle more work (current? ) than we ask it to do. Overrating doesn't harm things, while underrated contacts will fail too soon.
Often the choice involves what is handy to find in the size and shape wanted and also keeping the price down. Bigger coils with bigger contacts often cost more but not if one has a salvage relay on hand?/
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post #8 of 10 (permalink) Old 07-31-2018, 10:03 PM
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There are a lot of companies that package up everything you might need already if you're interested in going that route. Something like this (and various other "kits" made by them or others) PumpStopper Kit

If you want to piece it together yourself you can if you're comfortable with this stuff, and/or willing to research and learn a bit more. Your description above is the right general idea in that the relay acts as a switch to turn the hot lead on and off and the float switch can complete (or disconnect) the circuit. But its a little trickier than just splicing the relay into the hot side of the wire.

I think the tricky part for most is wrapping your head around the fact that the relay itself needs power (typically 12v or 110v) and the item you're looking to turn on or off also needs power (likely 110V in your situation but most can control a wider range of voltage). So you'll now have to have 2 things plugged into the wall in order to control the single end device. The wiring for it all goes through a relay socket which can be a bit tricky if you dont pay close attention.

This relay here is a 12v relay (the relay needs 12 volt power for itself and can then turn 110v power on or off to something else) and is rated at 5 amps. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

This one here is a 110v relay (the relay needs 110v power for itself and then controls a 110v device and is rated at 10 amps. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

You want to make sure the device you're trying to turn on and off doesnt exceed the amperage rating of the relay you choose. The wiring itself is a little tricky. I can never remember exactly which posts on the relay socket get what and always have to dig around for the diagrams I've drawn up when doing these. I think its referred to as a latching circuit if you want to try to find it.

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post #9 of 10 (permalink) Old 07-31-2018, 10:14 PM Thread Starter
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Found this one. It accepts 110v/ac so it will hold the power through the plugs. But.....idk

The coil says AC 110V

Contact says AC 240V/10A

Seems odd for the contacts to hold more power than the coil though.....

I understand that the relay itself needs power. Which is why I want it to kill power to a 3 plug cord. That way I can have power from the wall to power the relay and the other plug to power the cord.

Then the switch triggers the relay pumping power to or canceling power from the cord via the switch.

The photos in the first post are the of the equipment I plan to use. I'll do some more reading and see what I can come up with.
The wiring part for me is easy, I just struggle with power matching.

75 watt pump
300 watt heater
25 watt light

Floats say 50w/0.5amp max to trip relay

Relay and cord powered by 110v/ac

I like the link to the one you can buy as a kit, but I'm more worried about my sump running dry than I am the tank over filling. My tank can easily hold the extra 12 gallons of water without it flowing out. This is due to the height of my canopy compared to tank/water level height.

I appreciate the patience of you guys...lol
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Last edited by Darkblade48; 07-31-2018 at 11:53 PM. Reason: Please use the edit function for back to back posts to keep threads cleaner
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post #10 of 10 (permalink) Old 08-01-2018, 12:15 AM
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You may not have a real problem with the relay you mention as it is very much over sized. The coil of the relay can stand 110 and that is okay and the contacts are more robust/bigger than you may need The rating being bigger is okay as it just means they used heavier/larger contacts and those contacts can handle up to 240 volt and up to 10 amps. All that means is that they won't heat up at the higher voltage and they won't burn/corrode as soon as one rated for maybe 5 amp! Kind of like a car that goes 100 MPH but fine to drive it fifty! Little bigger/ little heavier but certainly able to do the job? The only problem is to not rate high enough. Put 220 into a relay rated for 110 and the points may be too close and arc or the plastic mounting may melt.
Think of relays as being two parts. First part is how much power and current it takes to move the relay contacts closed. so if it is a 110 relay, use 110 and then the rating will tell you how much current it takes to do that part. If you are plugging into the wall, you will have at least 15 amp available, so that is not usualy a problem.
Then the second part is how much voltage and current the contacts are made to handle. relays with contact rated way high is not a problem as they are just able to carry more, not required to if you don't need them to do it. One rated 220 and 10 amp is a big truck if you only need 110 and 1 amp!
But I fully agree that is can get to be a big headache, so I often get down to drawing it out in pictures!!!
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