Boiler Level Switch

[vederstein]

I have a problem.

I'm trying to add an automatic boiler feed to my monotube boiler. Due to the small size, options like floats are not really feasible.

I've seen people use a spark plug such that when the (non-pure) water reaches the plug, the water bridges the plug's gap and closes the circuit.

I started with this design and it didn't work. Thinking that the spark plug's electrode had a high impedance, I created my own out of brass.

Still no luck.

After some investigation I have the following data:

When the circuit is open, my resistance is off scale (no suprise).
When the plug is immersed in water, my resistance is about 100 kohm.

So, my (tap) water is too pure?!?!?

Does anyone know what circuitry I'd need to take this reduced signal back to run a relay where I could run the boiler feed valve?

Thanks,

...Ved.

 

[Jyman]

Hi Vad,

At work I use a relay coil connected in line with he probes, and that closes the contacts for the higher voltage pumps to come on. But as for lower voltage I can't help you with that one.

Jon


Sent from my iPhone using Model Engines

 

[Herbiev]

Try adding some vinegar to the water to decrease the resistance. It sounds like your water is too pure

 

[RichD]

There is a small IC chip NE555 that you can configure to sense the change on pin 5 and trigger a relay or transistor. Go to Williamson labs to study it.

 

[vederstein]

I tried the vinegar. It helped lower the resistance (about 4 k-ohm), but not enough.

I'll look into the 555 timer. IC's aren't me thing, but perhaps I can figure it out.

...Ved.

 

[canadianhorsepower]

I tried the vinegar. It helped lower the resistance (about 4 k-ohm), but not enough.

I'll look into the 555 timer. IC's aren't me thing, but perhaps I can figure it out.

...Ved.

Hi Ved
I teach in Robotic Engineering and I could build a circuit for you free
put I need some kind of drawing of what you want as far as operation
and the mounting you want to use
cheers

 

[vederstein]

My brother-in-law found the following on Instructables.com. I'm going to give it a shot:

http://www.instructables.com/id/Simple-Water-Sensor/

...Ved.

 

[kf2qd]

Try adding some vinegar to the water to decrease the resistance. It sounds like your water is too pure

You really don't want to add acid to boiler water. You are trying to not have to deal with corrosion. Most boiler treatments are bases.

Need a transistor amplifier circuit to detect the 100K. Problem is, some water will stick to your sensor and that could prevent it from changing state as the water drops. Other option is an optical sensor on a sight glass.Focus changes as the water drops.

 

[vederstein]

Some success!!!

Considering I don't know what I'm doing, today was a big breakthrough. I got the sensor circuit to work, with a modified spark plug as the water probe.

Now, the next step is to test it on the boiler, then if successful, solder up another one on a proto-board and install into a small enclosure.

...Ved.

[ame]http://www.youtube.com/watch?v=WC3BPyKblYc[/ame]

 

[kvom]

How is water being forced into the boiler under pressure?

 

[vederstein]

How is water being forced into the boiler under pressure?

I have Chinese 12VDC pump that was meant for RV use. It has a built in pressure switch that shuts off at 70psi.

(I apologize that my printing looks like it was done by a 8 year old although I'm 43. For alas, I'm left handed and have no artisitic ability - a double whammy.)

Crap!! I just noticed I sketed the check valve backwards. But you get the gist.

 

[vederstein]

From breadboard to the final, soldered version.

The task is done!