First off,
Amazon is delaying items that are not essential, but I just ordered all of the below to build a few more of these for friends, and got them in 3 days instead of the normal 2. It really all depends on where you are located. Also, ignore the crude paint sketches lol. I am not an artist.
List of items you need from
amazon. Most of the others you probably have lying around or at least something comparable.
USB powered water pump. I use the one below and it works well. I have also built these for friends on the hobby and they have had no issues either.
Float switches. I like these as they have not failed yet. Probably will now as I just jinxed myself. They are sealed and the wire is aluminum and not copper. (even though the wire is sealed covered with insulation, don't want to take a chance.)
Other items:
Old salt bucket or something else to store your RODI in.
Liquid electrical tape or heat shrink and silicone works also.
Old USB phone charger.
2 suction cups (optional)
piece of scrap acrylic or something similar.
Super Glue Gel or similar
RO tubing or even flexible airline for a bubbler works.
Prep Work -
1. Build the bracket the will hold the float switches. You can do this with the scrap piece of Acrylic. A heat gun, small torch or even a lighter will work to heat the piece and allow for you to bend it. You can bend it at both ends and make the bracket a hang on, or use some suction cups to make it stick to the side of the sump. Either way and be made adjustable. The suction cup method is easiest, but it can fall down if the suction cups are not the greatest, this is why I use 2 of them. The hang on method, can be adjusted, but you need some way of making it adjustable. Slots and zip ties, holes and platic screws into threaded holes, whatever you can come up can work lol.
2. Once you have the bracket made, you will need to drill 2 holes in the bracket for the float switches, and 2 more for the suction cups if you are using them.
3. When the bracket is made, it should look like the below. Again, excuse the crudeness of the drawing lol.
Again, if you make it a hang on, the top will have the bend to allow it to hang from the topside of the sump.
When this is complete, you can begin the wiring.
1. You will need to tie 1 lead from each float switch to each other.
2. twist the wires together well and fold them over themselves.
3. Apply a good drop of super glue gel to the wires. Let that dry.
4. Apply a small amount of liquid electrical tape over the area. If you do not have that, but have some heat shrink tubing and silicone, be sure to slide the heat shrink over the wire before twisting together and gluing. Apply silicone and then slide the heat shrink down over it and apply some heat.
5. When all of that is done, you are ready to build the lead to break the negative feed from the power supply to the pump.
6. somewhere on the USB lead from the pump, you will need to remove the outer insulation from the lead. Small knife or razor works well. Just slice off a small bit at a time, until you see the red and black wires underneath.
7. Once you see the wires, you can work it so that there is more of the wires showing. You only need about 1" of the red and black wire showing.
8. Now you need to cut the black wire in two and strip the ends of each a little.
9. Connect one lead from the float switches to one end and the other lead to the other end of the black wire you just cut and stripped. Apply super glue to the wires after they are twisted together, let dry and then apply liquid electrical tape to that.
10. For the RO feed line or air tubing, the little feed out of the USB pump is a hair smaller than the RO tubing most of the time, but can be larger. Either way, you can gently heat one or the other and enlarge it with a pen or pencil.
11. You then apply a small bit of super glue to the 2 and slide one over the other.
12. Your Top off feed does not need to lower than the maximum water level of the bucket. This could make it siphon utnil the end of the tube is level with the water level. A way around that is to use a small piece of pipe that comes up out of the sump, but does not go down too far, and then put the feed tube in that. That is if you care about hearing the top off run.
13. When all of that is dry, you now have an ATO that has redundancy.
It does need to be noted: You will need to remove the plastic clip that holds the float on the bar and flip the float for at least one float. You can check this with a multimeter (set on ohms) to see when the float is open or closed. You want the bottom float to be closed when it is down and the top closed when it is down (down as both closest to the water level). The bottom will need to go to open when it gets as far as it can travel to the bracket.
These little things work great, and they have redundancy in case the first float fails, something gets in its way, etc. The second float goes up and breaks the circuit as a back up.
Last but not least, as some have asked this. "What happens if the leads get damaged and they are open in the water?"
It is 5v feed and you are using the negative end of the power feed. It will provide a ground for the tank, but that is it.
Here is a pic of a rough wiring look and a rough look at the setup.