Simple Tank Fill Control

[MikeTranch]

I used two electric float switches, a 12V relay, and a 12V solenoid valve to provide silent tank fill control.

My application is RO water for a large capacity high output ultrasonic humidifier, to eliminate white dust. But this info can be applied to control filling any tank in general.

I installed the RO Buddy 75 GPD system, float switch directly into the 5 gal humidifier tank. It all worked great but the RO system was fairly noisy as the float switch was closed. The sound was prolonged for many minutes. Annoying during the day and enough to disturb sleep at night.

My solution was to add two electric float valves in the tank. The lower one closes the circuit when the water level is low. The upper one opens its circuit when the water level is full. A relay is used for two purposes. Firstly, the solenoid water valve draws 2.4A, too much for the electric float switches. The relay has 10A contacts. Secondly, the relay performs a latching function, to keep filling the tank when it rises above the low level. The latching function is released when the upper float switch opens. I used a 12V 3A wall wart I already had. It's all working great. Note the RO float valve is higher in the tank than the upper electrical float valve. So if the solenoid water valve ever got stuck open for any reason, the RO float switch would close and prevent tank over flow.

Here's my schematic and some photos. I have many more detailed photos if requested. I can also share links to the components that I used, if requested, and if allowed on this forum. I'm new here, don't want to break rules on my first post!

 

[Mebbid]

So am I understanding correctly that the RO system plumbed directly into the humidifier with a float valve which was making noise for quite a while after it was full prompting this build to reduce the number of times that the ro system ran?

It's an ingenious solution, I like it.

 

[MikeTranch]

So am I understanding correctly that the RO system plumbed directly into the humidifier with a float valve which was making noise for quite a while after it was full prompting this build to reduce the number of times that the ro system ran?

It's an ingenious solution, I like it.

Yes, the water controlled solenoid that came with RO Buddy 75 GPD kit was vibrating loudly as the included float switch approached the turn off level. I added the electric solenoid water valve at the inlet of the RO system. Note the electric solenoid water valve gets fairly warm when energized. I placed a Bluetooth temperature monitor on it, so I can plot the temperature versus time. With my setup and humidifier running lowest setting, the tank typically refills about every 8 hours, and takes about a half hour to complete. I placed both switches fairly high in the tank because I was planning only running the RO system during the day and wanted enough water in the tank to last all night. As it turns out, the system is now so quiet I run it 24-7.

 

[MikeTranch]

So am I understanding correctly that the RO system plumbed directly into the humidifier with a float valve which was making noise for quite a while after it was full prompting this build to reduce the number of times that the ro system ran?

It's an ingenious solution, I like it.

Yes, and also, good catch. With the included float valve, it would cycle much more frequently. With only that one float, there is effectively no hysteresis. That is essentially what using two electrical switches provides, hysteresis.