ECN Forum Forums Technical Discussion Electrical Theory and Applications Help with irrigation control circuit design

Try these people: http://www.liquidlevel.com/products_switches_standard_vt_LS-14-180.asp

A customize plastic float switch assembly that turns on at 2 feet and turns off at 6 feet is approximately $300 to $400. The float diameter is about 2" OD.

Larry C

Scott, a drawing would be great if not too much trouble, I'm usually pretty good with control wiring but for some reason this problem is confusing me.

Greg, I need the pump to shut off at high water, I guess high water is not really the right terminology as it's not a high water condition it's where my water level needs to be.

Kjay, I have never seen an electrode system, I bet thats what was here at one time but they are using the electrodes to carry line voltage now.

OK no problem, you just need to use low water "on" switches and wire the bottom one to the relay coil, and N/O side switch through the upper one to turn it off.

http://esteroriverheights.com/electrical/switch.jpg

Years ago I installed a 120 volt electrode system. It used an isolation transformer. Maybe the isolation transformer is missing on your system.

http://www.gemssensors.com/content.aspx?id=2258

LG,
Go to this site and download the instruction bulletin and PDF. I'm used to dealing with them in the differential pump down mode (F2, top row). Your application would require the pump down or up (G2, middle row), or pump up mode (H2, bottom row) mode. I would normally use the H2 for your app but you said there is another pump location that you pump down. So it is the choice of H2 with a spare contact or G2 which goes both ways.

The conduit serves as a still well besides protecting the probes. In your case, the pump contactor(s) would be energized through N.C. contacts. When the water reaches the high level probe, current from the secondary of the integral transformer, flows through the water between terminals 9 & 10. This energizes the relay to open the N.C. contacts and stop the pump(s). Since a jumper is added between terminals 8 & 10, current will flow between 9 & 7, through the Normally Open, Held Closed contact to 8, through the jumper to 10. This will keep the relay energized and the pump(s) off until the water clears the low level probe.

I just offer this description should you decide to stick with the original method. I don't want you to think that it is a dangerous, home brew technique. I have them in 2 locations where an incredibly stupid bubbler/pressure transducer scheme is used as primary control. Some designers have a little too much time on their hands.
Joe

What you really need is a RADAR tank level indicator mounted in a pipe. Sure, it's probably 2 figures more than the other solutions and you don't really need to know the canal level to that high of a precision, but it's also really cool

Joe, yup thats what was there (well I feel like an idiot now) but they were made my magnatech, they were both burned up (power company had a major problem in the area). I showed the thing to 8 different electricians and 3 supply houses, nobody knew what it was except it being a contactor and transformer in one. The existing one had 120v as primary and 240 as a secondary voltage. So these controls are safe when they are putting 120v into water? It just doesn't sound right.

LG,
I'm glad I was able to help. Believe me, it took me several minutes to wrap my brain around how they worked when I first encountered them.

Now let's take a look at the safety angle since it bugged me too. If you have it contained in a grounded conduit / still well with a grounded lowest electrode, you're grounded! So 1 end of your isolated and current limited secondary is now ground referenced. Once the water reaches the highest electrode, you now have a voltage divider of the water/probes and the relay coil. I won't pretend to know the voltage gradient around that conduit and probe. You could short out terminals 9 & 10 with your meter on AC Amps to determine maximum current the system can deliver. Of course, the current through the water and probes would have to decrease as the voltage drop across the probes increased. Your worst case there would be if you jumped in the canal and grabbed the grounded and hi level probes while the level was low. (See posts in other areas pertaining to "Darwin Awards" and "Natural Selection"!) If our typical circuit current is less than what would trip a GFCI, no worries! If we figure there would be enough shunt current available to hurt somebody, post a sign...
DANGER!!! NO SWIMMING IN CANAL!!! ELECTRIC EELS!!!
Joe

Here is the "Start / Stop" Control Schematic:



I included a Control Transformer - to step the Control voltage down to 120V or whatever.

Additionally, I included a HAND-OFF-AUTO (HOA) Switch, just for fun.

Sorry it took so long.

Scott