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Sprinkler valve solenoid amps?

Discussion in 'Electronic Repair' started by Dallas, Aug 25, 2006.

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  1. Dallas

    Dallas Guest

    I've got a real head scratcher.

    Long story short: 18 zone, 24-volt AC commercial sprinkler controller

    One valve on the system won't operate anymore after running fine for years.

    The valve operates when connected to a battery operated testing unit.

    Voltage at the controller terminal going out to the zone shows 29 volts.

    The wires from the controller at the valve (guessing 200+ foot underground
    run, 14 gauge wire) show 27.4 volts.

    There's enough current to give you a tickle if you grab the wires.

    Connect the 27.4 volts to the valve and nothing happens.

    My degree was in Business so I start to get fuzzy at this point. Could one
    of the wires be missing some insulation somewhere underground and drawing
    off enough amperage to keep the solenoid from actuating while still showing
    27.4 volts?

    Is there anything that could happen to a solenoid coil that could make it
    demand more current to operate?

    Sadly my $30 meter doesn't have an amperage function. Would hooking the
    voltmeter in series with the circuit tell me anything?

    Can anyone give me a clue as to what's going on?

  2. Dallas

    Dallas Guest

    Sorry about all the extra carrage returns in that post... I really wasn't
    trying to be dramatic, I cut and pasted from MS Word and that was the

  3. ampdoc

    ampdoc Guest

    Loading. You are testing the wire in a no-load condition.

    A nick in the wire somewhere allowing water to enter could have caused
    corrosion, and made a resistor of your wire. When you check the end of it,
    even with your finger, you have not applied a load to the line. Try
    measuring the voltage at the valve when the wires are connected. I bet you
    will find that due to resistance in the wire, you have too much voltage drop
    for the valve to work.

    If so, your best option is to replace the wire.

  4. There might be a cut in the wires so that only one or two strands are
    carrying the voltage. Without a load (the valve) voltage looks fine but
    when the valve is attached voltage could plummet. Measure the voltage
    before and after the valve is attached. Also try the valve at the
    controller rather than the lawn; the controller might be defective.
  5. Guest

    Also dont overlook possibility of a stiff mechanism connected to the
    solenoid, or a stiff solenoid due to leakage and corrosion.

    A good way to drive solenoids is to use a capacitor to give them an
    initial pulse of 2x rated voltage, which very rapidly drops to rated
    voltage from the supply.

    Really you just need to work it thru, divide and conquer until you know
    where the problem is.

  6. G

    G Guest

    Hello Dallas. When you say "The wires from the controller at the valve
    (guessing 200+ foot underground run, 14 gauge wire) show 27.4 volts.",
    do you mean WITH the solenoid connected? Connected is how you need to
    measure that voltage (under actual operating conditions). There is
    where you may find that the voltage sags bad, causing or aggravating the
    inability of the valve to a starting point knowing what you
    have for test equipment (so far).

  7. default

    default Guest

    You want to measure the voltage with the solenoid valve connected to
    the power source. They use solid state drivers (triacs) that will
    leak enough voltage to appear to be working when they still won't
    operate the load if there is no load connected)

    If it still doesn't work, switch that channel to another zone and see
    if it will work that zone.

    One assumes you tested the water supply?

    I'd also see what an operating valve uses (what voltage is across it).
    Choose a valve the same distance from the controller and measure that
    voltage while it is on. 27.5 sounds too high considering nominal is
    24 and you should drop some voltage in the line - I know you think it
    is connected but that sounds like it isn't. (wire nuts?, corrosion?)

    Failing all else, bite the bullet and replace it (or physically switch
    it with one of the other's - if that's an option - to see if the
    problem stays with the valve).
  8. Dallas

    Dallas Guest

    Thanks to all that replied.

    Yes, testing the voltage across the circuit with the solinoid connected
    destroyed the voltage (near zero).

    We finally found a damaged point in the underground wire where all the
    current was leaking off into the ground.

    Thumbs up!

  9. CRaSH

    CRaSH Guest

    Took ya long enough Varmit! d:->))
  10. James Sweet

    James Sweet Guest

    It wasn't leaking off into ground, there just wasn't a good path for any
    appreciable amount to be drawn by the solenoid.
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