DIY ATO

Bill of Materials

One 12 Volt DPDT Relay (Ebay, Radio Shack, etc.)

One small project box to house relay and 110 VAC wire junctions (Radio Shack)

Two float switches (Marine Depot or BRS)

Two plastic medicine bottles to house the switches (the medicine chest)

One 12 VAC power supply (I used a cell phone wall charger, the output voltage is on the label)

Small submersible pump (Harbor Freight)

Tubing to fit the pump's outlet and of a length to go from your ATO reservoir to the spot in your sump where you want the ATO to feed (Lowe's)

Short extension cord with the proper plugs for your pump (some require two, hot and neutral; others require three, hot, neutral and a ground)

Electrical shrink tape (helps keep the water out and looks more professional)

Wire ties and some egg crate

Tools

Drill and bits

Wire cutters with wire stripper

Razor knife

Wire connectors and tape (if you don't solder them and use shrink tape)

Soldering iron and LEAD solder with rosin core

1. Determine where you want to mount the relay box to keep if out of the way and protect it from getting damp

1. Determine the routine of the extension chord from the outlet to the ATO pump location in your reservoir

2. At the point on the extension cord where the relay box will go, slice the outer skin of the cord. Two wire cord my not be marked with different color wires, but select the one that goes to the hot side of the plug. On a three wire cord select the black wire (hot). Once you have separated the wires cut the hot wire and strip it back 3/8 inch. Solder or use push connectors to attach both pieces of the hot wire to the 110 normally closed prongs on the relay.

3. Drill hole in the sides of your bottles to allow water to enter and exit. Drill a hole in each cap and mount the float switches with the wires outside the top.

4. Connect one wire from each of the float switches together. This should join the two switches and leave you with one wire coming off each. The switches don't have a polarity so it doesn't matter which wire you use. Connect one of the two remaining wires to the 12 VAC prong on the relay, solder or use push connectors. The other float switch wire is connected to one of the wires on the 12 VAC power supply. Don't forget to put the shrink tape on the wire before you connect them, I like to solder them, but you can use pinch connectors of the correct size. This leaves you with one wire from the 12 VAC power supply. This wire is connected to the other 12 VAC prong on the relay,

5. Mount your bottles to a piece of egg crate at the correct height for the ATO to turn on with wire ties. Make sure they don't interfere with the movement of the float switch. Now mount one about an inch higher. Place the caps (with the float switches and wiring attached) on the bottles. Place it on the sump and secure it from moving. I use a small plastic clamp and clamp it to the side of the sump. Plug in our power supply and extension cord. Place the tubing on the pump and plug the pump into the female fixture on the extension cord. Put the pump in the ATO reservoir. Now adjust the height of the bottles the switches are in to get the correct level to turn on the switches.

6. Route the feed tube to the correct location in the sump and secure it with wire ties so that the outlet is above the highest water level. This will prevent the ATO from siphoning water from the sump back into the ATO reservoir when it shuts down. This is pretty important since you can overflow the ATO reservoir or if it only back siphons a small amount it will likely trip the float switch and cause the pump to come on again in a continuing cycle of fill, back siphon which lowers the water level enough to cause the pump to start again, renewing the cycle over and over.

I like to check the relay with a multimeter to ensure I have the correct prongs before connecting the wires. You can touch the 12 VAC leads to the proper prongs on the relay and hear it switch. Leave them on and connected and check with the Ohms meter for the correct set of 110 prongs. They should have continuity with the 12 VAC connected. When the 12 VAC supply is removed the 110 prongs should be open.

Be cautious, water and household voltage can create a dangerous combination. Ensure all wires and connections are not in the water or where water will drip.

Wiring diagram