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Strange, Possibly GFCI, Failure ??

Discussion in 'Electronic Design' started by Jim Thompson, Oct 13, 2005.

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  1. Jim Thompson

    Jim Thompson Guest


    Intermatic (motor-driven clock) timer fed from GFCI into 12VAC
    lawn-lighting transformer

    When timer reaches turn-on point it appears that voltage drops enough
    that timer stops turning, so lights don't turn on.

    Manually "pushing" timer thru turn-on point, lights come on just fine,
    with transformer "thumping" from surge, output voltage is correct.

    Timer runs just fine on another outlet

    Is it conceivable that GFCI is resistive unless loaded heavily?

    How would you test?

    ...Jim Thompson
  2. I read in alt.binaries.schematics.electronic that Jim Thompson
    Maybe the contacts don't 'wet' on low load current.
    Put a lamp in parallel with the transformer primary.
  3. I don't think so. They are pretty much wire and contacts all the way
    through- and I don't think the sensing coil adds enough inductance to
    bother things with a single turn primary. Maybe its just very marginal
    and perhaps is on the other half of the 120. Have you measured the
    voltage at the outlets?
    Our fancy Loran one got its timer fouled up (I think the #$(*#$
    earwigs got into it) so I put an inexpensive Noma electronic timer
    ahead of it, and it's been working fine since, and switching some high
    voltage exterior lights at the same time. It uses a dirt-cheap 5A
    relay inside, so it will eventually fail, even at 2 operations per
    day, but that's no big deal.

    Best regards,
    Spehro Pefhany
  4. Joerg

    Joerg Guest

    Hello Jim,
    That's odd. As Spehro said GFCI are pretty "digital" devices. Either the
    internal relay is on or off. If half on it would go bzzzzt.

    Could it be that the timer is in a slightly different mechanical
    position between the two outlets? If it's one of those black hardware
    store editions with a lid over them they have plastic gears. Our
    experience so far: After a few years they make faint but weird grinding
    noises, after another year they work only when Mars and Venus are in
    perfect constellation, a few months later they are toastissimo.

    Listen to the timer closely. If the gear noises are a very faint and
    regular hash it may be ok. If it sounds like a pulsating grind it's on
    the verge of seizing.

    Regards, Joerg
  5. Bob Noble

    Bob Noble Guest

    Sure it is conceivable, but not likely.
    More likely that a wire feeding the system has a bad connection that is
    sucking all your voltage when you increase the current draw, such as would
    happen when the motor is pressured to turn the switch on.
    My experience with GFI's is they either work or they don't.
    Many times I find that people don't tighten the wires to them very well.
    But even then, they either work or they don't.
  6. Jim,

    First, use your DVM to confirm your suspicion that the voltage drops at the
    motor when the load goes up just before it trips on. If it doesn't, then the
    timer has a problem as others have suggested.

    If it does, then backtrack to the GFCI and check the voltage from the output
    screw to neutral to see if it is there. If not, then you've got a loose wire at
    the output of the GFCI or somewhere downstream toward the timer.

    If you see the voltage drop at the output screw of the GFCI, then assuming you
    are using an outlet GFCI, check from the input screw to neutral to see if the
    voltage drop is also at the input. If it is there too, then your problem is at
    the input connection to the GFCI or upstream toward the breaker panel. If you
    are using a breaker style GFCI or the voltage drop isn't at both sides of the
    outlet style GFCI, then the GFCI is likely at fault.

  7. Guest

    Wait until it's stalled and connect a jumper (or two, as needed) across
    the GFCI.
    (If you don't like the taste of electric juice, wear rubber gloves.)
  8. RoyalHeart

    RoyalHeart Guest

    Jim, just for comparison, I have a LV landscape lighting system as well.
    It also uses an Intermatic (Motor-driven) timer/transformer pack. The
    pack is plugged into a GFCI outlet, via an nextesion cord, on a circuit
    dedicated to yard outlets.

    The timer/transformer pack is the only utilization device on that brach
    circuit, and the timer operates just fine.

    From this, it is possible that the timer may be defective, or that a
    bad connection exists at the GFCI contacts or screw terminals, as others
    have suggested.

    Hope this helps.

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