Relay to Swap Auto Pumping to Manual

Before I found out about the CBW controllers, I programmed a Unitronics V120 industrial PLC to be an irrigation controller but a very manual controller. Power it up and enter how many minutes you want the pump relay on for and hit Run. When it ends, hit Run and it will run for that same length of time. If you want a different amount of time, power it off and back on. Mine has a custom branded overlay for some Aquafine Corp. At least it has to do with water. They put Start/Stop text on the #1 button so I used it as a start/stop function for the pump.

It would still be handy to have it along with the new CBW controller relay but I worry about using both and the possibility of having the pump powered from two different sources at the same time.

SPDT relay to the rescue. SPDT = Single Pole – Double Throw. Two wires for the coil, a common and two outputs, NO – Normally Open and NC – Normally Closed

Powering the coil activates the relay which opens the normally closed and closes the normally open.

Power a SPDT relay along with the pump when V120 turns on pump
NC opens and pump gets power from NO which closes.
When manually set time runs out, V120 shuts off relay and CBW is now active again via NC.

Easier than reversing polarity on a DC motor.

Here’s the system at rest. V120 OFF – Controller can power pump.

12 vdc+ is applied to the relay when V120 is supplying 12 vdc+ to pump which prevents 12 vdc+ coming from Controller

Again, I programmed a Unitronics V120 industrial PLC to be an irrigation controller but a very manual controller. Power it up and enter how many minutes you want the pump relay on for and hit Run. When the run cycle ends, the relay goes back to state of rest and controller can now send 12 vdc+ to the pump.

This will be handy for fertigation or any other time I just want to run the pump for a short time without walking to the shed, waking up the PC and either setting a one time schedule for 30 minutes etc or turning it on manually in which case there’s a chance I’d forget to turn it off and it would pump all the water out of the tank and keep running – btdt.

If the V120 has power, I hit run to make it run however long it did when last set. If I want a different amount of time, turn the V120 off and back on and punch in some minutes and hit run. Another handy time is when I’m out there and see one bed that could use watering. Turn off the valves to the other rows and run the V120.

I already have a weatherproof electrical enclosure the V120 will fit in. I just need to cut a square hole for it.