I'm setting up a watering system in my greenhouse. This is a 12v DC system.

I have three timers, each controling its own solenoid valve + a shared water pump.

How do I prevent current from going to the other two valves when a single timer (and its valve) activates?

I've tried experimenting with Schottky diodes which I have plenty of - but with no luck. Its been mostly trial and error since I am not very strong in the theory of this.

valves and pump

A very (most likely naive) idea of how this should work. I had the idea / understanding that Schottky diodes could prevent current from "going back" / "backfeed" to the other valves. However, this obviously does not work.


The diodes I have tried to work with (1N5822):



enter image description here

  • 4
    \$\begingroup\$ why would a valve not connected to the same timer turn on? could you show us a diagram how you are wiring the system? \$\endgroup\$
    – Rodo
    Jul 2, 2021 at 16:49
  • 1
    \$\begingroup\$ A schematic or wiring diagram will help you get a good answer, but I think you probably need 3 relays (with coils in parallel with solenoids), and N.O. contacts in parallel to turn on the pump whenever any valve is opened. What are the voltages? Is this DC or AC? \$\endgroup\$
    – Theodore
    Jul 2, 2021 at 16:56
  • \$\begingroup\$ Updated question based on comments. \$\endgroup\$
    – sbrattla
    Jul 2, 2021 at 17:21
  • \$\begingroup\$ You dont need diodes at the negative Rail (0V) of your system. It should work with the diodes you have added. I dont get why it does not work. \$\endgroup\$ Jul 2, 2021 at 17:33
  • \$\begingroup\$ You have all of the right parts, but the connections vary depending on the details. What is the "timer"? Photo / web page? What is the power source for the system? One 12 V output power supply for all three timers, or one per timer/valve? \$\endgroup\$
    – AnalogKid
    Jul 2, 2021 at 18:10

1 Answer 1



simulate this circuit – Schematic created using CircuitLab

Figure 1. Each timer drives its own solenoid and the pump. D1 to 3 prevent backfeed from one solenoid turning on the others.

  • \$\begingroup\$ Thanks for the schematic - it works now! I really thought that I had tried it this way, but I obviously can not have done that since it did not work until now. Thanks! \$\endgroup\$
    – sbrattla
    Jul 2, 2021 at 19:02

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