auto top off (ato) circuit

[beaslbob]

Oh no not another ato circuitl. LOL
This circuit uses two double pole double throw (dpdt) relays to control a pump in the ato bucket to keep the tank water level between two level switches in the tank.
The relays are 12v 'power' relays one wired as latching relay (left relay) and another two stop operation when ato bucket water level is low.
As the tank level goes down the high level float switch make contact contact but is blocked from the ground signal because the left relay has not been energized.
As the tank left goes down eventually the low float switch makes contact and the left relay is activated turning on the ac to the ato pump. This also connects the ground through the other pole to the high level float switch.
As the tank water level rises the low float switch opens but the relay remains activated because the ground signal is now passed through the high level switch and the energized left relay. Which keeps the left relay energized.
When the high level switch is floating the ground signal is broken, the left relay deengerizes, and the ac to the pump is turned off.
When to ato water level is low the right replay is activated isolating both tank float switch ground from the left relay.
I used relays with leds that light when activated. So when the left relay led was lit the pump is pumping. When the right led is lit it forms a signal the ato is low on water.

Some approximate ebay prices (as of nov 2021)

12 v dpdt relay and socket $4 two required

float switches $2 (three required)

Water proof project box $6

120v to 12vdc adapter. $8 or so.

local sources

door bell solid wire $11 for 100 feet two wire.

return pump (make sure it can pump at least 10-15 foot head) $30-$50 or so. A return pump from an old aquarium sump is probably too strong. Best to return the water to the tank slowly.

misc nylon stand offs to mount the 12 volt adapter circuit card

What I did was tear apart the 12v adapter and mount the circuit card on nylon stand offs in the project box. Then wire the relays as shown. I also mounted the tank level switches in pvc pipe to prevent algae and/or snails from interfering with switch movement.

One thing I found out is be sure you drill holes at the top of the switch containers. At first I drilled hole belose the float swighted but no above. I found out air is trapped preventing water from floating the switch. LOL

Mounting the relays in a socket made wiring much easier with no soldering required and if (when) a relay fails three years from now or so, you can just replace the relay.

I suspect you could reverse the ground and +12v to the relay coils and it would still work but haven't tested that. Perhaps electronic type can chime in and give my any warnings about connecting the grounds to complete the circuits.

For that matter any feedback would be appreciated.

 

[blaxsun]

It looks great on paper!

 

[beaslbob]

.all

All float switched complete circuit at low water and break circuit when floating higher
First the upper tank switch makes contact. the ground goes through the switch over to right relay over to the left where it stops.

 

[beaslbob]

As the tank water level continues to lower the lower float switch makes contact

Hopefully those colors are better. LOL When the lower level makes contact the ground goes through the right relay to ground the left relay. That activates the left relay, connecting the 120v to the ato pump, lighting the relay led, the upper relay to the ground also.

 

[beaslbob]

As the tank level rises the low tank switch opens but with the activated left relay still provides a ground through the upper float switch. So the pump continues to pump, the led is lit until the higher float switch rises and breaks contact.

 

[beaslbob]

and finally both tank switches are floating and the ato pump is turned off.

 

[beaslbob]

finally when the ato tank is low on water, the right relay energizes and prevents the tank float switched from activating the pump. Plus if the relay has an led it lights providing an add water signal.