Question about running sprinkler cable..

Discussion in 'General Electronics Chat' started by osx-addict, Jul 24, 2012.

  1. osx-addict

    Thread Starter Member

    Feb 9, 2012
    122
    9
    Ok.. One of my other tasks coming up.. I've got a house with two sprinkler controllers.. One for the front and one for the back.. I'd like to eliminate the front one and run that single front yard valve from the rear controller -- a wire span of perhaps 100ft.

    However, part of the line would need to be run underground from the front of the house (where the valve is located) to the rear of the garage where the controller is -- as they're separate structures. So, I've got existing conduit buried below grade in a trench I dug about 7-8 years back -- this conduit has three 12 gauge AC wires (IIRC) running through it to send AC from the house main panel to a sub-panel in the garage which in turn feeds power to outlets, lights, and whatnot.

    So, since sprinkler solenoids are controlled by AC voltage (24VAC if I recall), I was wondering if it's OK or not to run the heavy duty sprinkler wire through the shared conduit (a run of ~20 feet) along side the 110VAC already present.. I realize IF the solenoids were DC they might have some sort of signal induced on the wiring from the AC signal sine-wave but if they're both AC does that still happen and if so, would it cause any problems for a solenoid in this sort of situation?

    Thanks!
     
  2. #12

    Expert

    Nov 30, 2010
    16,354
    6,852
    Capacitive coupling will not interfere with a control wire to a solenoid, whether in phase or out of phase. The National Electrical Code will interfere if you read the part about control cables in a power conduit.
     
    strantor likes this.
  3. osx-addict

    Thread Starter Member

    Feb 9, 2012
    122
    9
    yeah.. I know.. You can tell I'm really not that interested in digging yet another trench! I looked at it a bit closer last night and it's probably not 20 feet -- might be only 15 and part of it would be to tunnel beneath a ~3ft sidewalk using a water blaster.. I might have to think this over some more..
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Sprinkler wire can generally be buried directly in the ground without conduit and you don't necessarily need to dig it below grade. A shallow burial is fine. I've had sprinkler wire in the ground for >25 years with no problems.
     
  5. osx-addict

    Thread Starter Member

    Feb 9, 2012
    122
    9
    Thx.. I'm aware that I can run it directly w/o conduit (PVC in my case) but I want to ensure that nobody using a shovel will accidentally cut it if they aren't sure what they're doing,etc.. Also, I'm not going to run it like my neighbor did his sprinkler lines -- literally inches below grade.. I can't believe he was that lazy! I could walk over to his house and pull one sprinkler head up and take the rest with it without much effort.. :eek:

    In my case I'd prefer a trench at least 1 foot deep.. We don't have to worry about a frost line here since it never freezes anyway (we're in So-Cal) or even gets below 40F most of the time..
     
  6. osx-addict

    Thread Starter Member

    Feb 9, 2012
    122
    9
    One more twist if you don't mind..

    If I wanted to use a transmitter/receiver to do my bidding -- using one of these binary transmitters and one of these for the receiver (4 channel mind you), I think I could make this work for about $200.. I've got one of these at home for an alarm system where the transmitter is connected to a PIR sensor (Optex HX40) and when it triggers movement it creates a binary output which is transmitted via the above module to the receiver which does it's business..

    In this case the roles would be reversed -- the binary transmitter would be attached to some glue logic that would take the 24VAC from the sprinkler controller and convert it to a binary "1" (if commanded on) or "0" (if off).. The remote valve(s) would then have the offending 4 channel receiver and when a signal comes in, would close a Form-C relay (part of the receiver) and apply 24VAC to the solenoid wires to open the valve.. The receiver would be setup to "follow" the transmitter -- holding the relay closed until the transmitter told it to stop. In this case, since I've already got a Toro controller with 24VAC transformer I could re-use the box + AC components to give me the power needed to not only open the valves but also run the receiver..

    The only thing needed would be the glue logic to convert a 0VAC signal to a binary "0" and a 24VAC signal to a binary "1".. In checking the specs on the transmitter, the following is mentioned which indicates no voltage higher than 3.3vDC should be applied to the binary switch input pin -- if I'm reading correctly :

    So. does this sound like an option that is do-able? Sure I can still dig a trench but what's the fun in that? :rolleyes:

    P.S. If you're wondering, these transmitter/receiver pairs are good for 1 mile line of sight per the company.. I've heard nothing but good things about these -- which are used mostly in the alarm sector from what I gather. I've been very happy with mine so far..​
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    You can generate the 3V nominal DC by rectifying the AC with a diode and capacitor filter, and use a voltage divider to reduce that voltage to 3V. 24VAC will give about 33VDC when rectified and filtered. Use a 200 ohm (to ground) in series with 2.2k ohm to get 3V. (You may have to tweak the 2.2k resistor value to get within the required limits of 2.48V and 3.3V so measure the voltage at the divider before you connect to the transmitter input).

    The 2.2k ohm resistor should be at least 1W size. The 200 ohm can be 1/8W.
     
    osx-addict likes this.
  8. osx-addict

    Thread Starter Member

    Feb 9, 2012
    122
    9
    Thanks! If I decide to go this route I may ping you on what parts I will select if you don't mind.. I've got an email into the sprinkler controller people to ensure that if I plug something in this fashion will not confuse the controller's fault detection logic which might make it shut that port down.. Hopefully it won't notice, but this company does have some interesting fault detection logic that can detect open's in the solenoid control lines and whatnot.. Not sure how it does that though -- perhaps sensing current flow or something..
     
  9. osx-addict

    Thread Starter Member

    Feb 9, 2012
    122
    9
    Ok.. Got a note back from Weathermatic who makes the sprinkler controller (an SL800 SmartLine controller if you're watching at home).. They said their fault logic would trigger IF the current exceeds 1A but that I can adjust the trigger up to 2A if needed (he told me how). I'm thinking this voltage conversion circuit would be well below 1A -- am I on the right track?
     
  10. osx-addict

    Thread Starter Member

    Feb 9, 2012
    122
    9
    Ok.. So, for the circuit that crutschow suggested above, I think it'll look something like the one mentioned here -- but with the voltage divider resistors missing.. Would it be a good idea to add a LM7803 or similar to ensure the voltage does not fluctuate too high -- but change the voltage divider resistors to drop the 33VDC down to something closer to 7-8VDC? Perhaps it's nothing to worry about.. Just curious..
     
  11. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    If you are worried about excess voltage you could place a 3V zener across the 200 ohm resistor.
     
  12. osx-addict

    Thread Starter Member

    Feb 9, 2012
    122
    9
    ok.. Will keep that in mind.. In talking with my better half late last night I think she was opting for the trench muscle building excercise & crawling under the likely spider infested house instead.. :(
     
Loading...