My limited knowledge of electronics allowed me to solve a 'problem' that I had with my sprinkler controller.

I wanted to run zones individually, but for some zones also wanted to run them together (in order to essentially have lower water pressure and throw the water to a different locations than what it would at full pressure).

So on the wiring to the controller I would, for example, wire the solenoid of one zone to the controller's zone1, and wire the solenoid of another zone to the controller's zone2 (There's a common wire that is also wired to the controller for all solenoids to complete a circuit). Then I would use two diodes to go from the zone1 wiring to zone3 on the controller, and from the zone2 to zone3.

Yay, it worked.

However, I noticed the solenoids were 'clicking' on any combined runs. I'm guessing this is due to a voltage drop? Is there a way for me to get the correct voltage to each solenoid?


EDIT: Here's a picture of what I did, very convulated to look at but, all I am doing is adding the diodes in at the controller, clearly I have no ide what I did :) I thought of the diode as a one way street, so when (in my example) zone3 is triggered the completed circuit (via the common wire - white) between zone1 and zone2, whereas when zone1 was triggered it would not go through the diode through zone3 and to zone2. Wiring

So the green wire(zone6) and yellow wire(zone5) go to zone3, so if I trigger zone3 they both go.

ADDED 2: enter image description here I think I almost have it, but I feel like my problem is that I have this white common wire coming back from all the solenoid valves, which I can't isolate. In the first diagram I can get what I want (but that isolates every second wire to each solenoid, which I can't do without digging up the yard). On the other diagram with the second wire common, I get undesired current flowing half the time to the unintended valve.

Am I missing something obvious, or is there no way around having the second wires isolated?

  • 3
    \$\begingroup\$ Please draw a simple diagram - it might help \$\endgroup\$
    – Andy aka
    Mar 27, 2014 at 15:56

3 Answers 3


You made one big mistake, which is to not put diodes in the lines from zone 1 and zone 2. When zone 3 goes on, it is now back-driving zones 1 and 2. Whether that matters and what kind of damage that could cause depends on the circuit. Apparently you got lucky, since zones 1 and 2 apparently still work.

Perhaps your system is driving the solenoids with AC. In that case the diodes are only letting power get to the solenoids every other half-cycle, instead of every half-cycle when the full AC is applied. That could possibly cause the solenoids to move enough to appear to work, but also to vibrate noticably at the power line frequency (60 Hz in the US, for example).

If the issue is AC, then there are ways this can be addressed. However, it makes sense to get more information about your system before going into details that could be totally irrelevant.


Now that is seems clear the problem is that the solenoids are driven with AC, we can talk about ways to get what you want within that framework. One way to do this is to put a full wave bridge after each zone output. That makes it DC instead of AC. The solenoids will still work fine on this rectified AC.

Now that you essentially have DC output from the zone controllers, do what you tried to do before, but this time do it right. The safe thing to do is to put a diode between each zone output and solenoid. If I understand your setup right, zone 1 would drive solenoid A thru a diode (after the full wave bridge, consider those part of the zone outputs now), zone 2 would drive B thru a diode, and zone 3 would drive A and B each thru separate diodes.

Added 2:

Here is a schematic of what I was referring to above:

Note the full wave bridge immediately after each zone controller output. That is D1, D2, D3, and D4 for the zone 1 output, for example. Each valve driven by each zone is then isolated with another diode. These are D9, D10, and D11 for zone 1, for example.

With this level of diode isolation, the same valve solenoid can be driven from multiple zones. For example, valve 1 could be connected both below D10 and D14 without those connections causing shorts or back driving one zone when the valve is driven by another zone output.

  • \$\begingroup\$ I updated the question a bit with more information. I'm not sure I know how to provide more information :). Let me know if I can. I'm not wrapping my head around how it is back driving (since my simple idea was that the diode makes it flow one way). If you think you could explain that in a different way for me, that would be nice. I'm researching it now :) Thanks. \$\endgroup\$
    – shawn.mek
    Mar 27, 2014 at 16:25
  • \$\begingroup\$ @shawn.mek Olin has it right; almost all home irrigation systems in the US run on 24VAC. The MOV's in the upper left of your photo confirm it. So, during normal operation, current is actually flowing both directions through the solenoids. With the diodes in place, it's like they're getting turned on and off 60 times per second. I would remove those diodes right away before the solenoids burn up! \$\endgroup\$
    – bitsmack
    Mar 27, 2014 at 17:12
  • \$\begingroup\$ Ahh!! Awesome. Thanks that extra bit of explanation helped me understand it a bit more. Hmm, would there be a way to actually fire two zones at once? I guess just bridging them would do that, but then I couldn't fire individually. I guess the real question I want answered is totally different that what I asked, but a GREAT answer anyways. If you think of a workaround let me know :) Thank you for the explanation. Sorry I can't upvote you guys. \$\endgroup\$
    – shawn.mek
    Mar 28, 2014 at 17:39
  • \$\begingroup\$ I'm trying to wrap my head around the wave bridge setup. Would there also be a wave bridge on the common wire? \$\endgroup\$
    – shawn.mek
    Apr 1, 2014 at 14:55
  • \$\begingroup\$ @shawn: See addition 2 to my answer. \$\endgroup\$ Apr 1, 2014 at 15:45

I had a similar problem recently.

I overcame it by wiring diode 1 to the controller circuit 1 with positive bias and diode 2 to the controller circuit 2, but with negative bias and then connected both to the field wire going to solenoids 1 and 2. In the field I put a diode 3 on solenoid 1 , with positive bias and diode 4, with negative bias, on the field wire looping on to solenoid 2 with negative bias. My supply is 24 V AC. When circuit 1 is on I get get the positive half of the sinewave through the 2 positive biased diodes and get sufficient voltage, half wave rectified, at solenoid 1 for it to operate. Solenoid 2 see's nothing as it blocked by the negative biased diode 4. When circuit 2 is on I get the negative half of the sinewave thru the negative biased diode 2, which give me sufficient voltage to operate solenoid 2, and solenoid 1 see's nothing due to it being blocked by the forward biased diode 3.

  1. Purchase two "Doubler" expansion units and wire at the valve box according to which valves you want to synchronize, utilizing the same hot wire for both "Doubler" units wired to different valves. https://www.youtube.com/watch?v=yCnlNXE0DBo
  2. Purchase "wireless" valve solenoids and replace what you have. Synchronize the valves you want at the computer /and/or sending unit programing. Note: Use as many "Doubler" or "wireless" units as needed; but keep in mind, there is only so much water and pressure in the existing underground pipes.

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