I guess I don't understand Rain Bird panel - valve hum & transformer hot

Discussion in 'Irrigation' started by gdeangel, May 20, 2013.

  1. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,323

    I change out solenoids when they trip the overload circuitry. If I ever did get into preventative solenoid replacements, it would be based upon operating current measurements, and not resistance.
     
  2. Mike Leary

    Mike Leary LawnSite Fanatic
    Posts: 21,896

    What the big guy said.
     
  3. 1idejim

    1idejim LawnSite Fanatic
    Posts: 9,313

    Well fellas, explain this to me.

    If your I=0.2 , what are your E & R values?
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  4. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,323

    the trouble with I = E/R, is that the 'R' you got with an ohmmeter measurement is not the actual "Reactance" at 60 Hz (Reactance is term that works in AC circuits, where current and voltage are not in phase with each other)
     
  5. 1idejim

    1idejim LawnSite Fanatic
    Posts: 9,313

    answer the question
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  6. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,323

    They are vector quantities, with a phase angle. We all know that any solenoid resistance we measure with an ohmmeter is going to be only a small portion of the actual operating impedance, due to the inductance of the solenoid coil and its magnetic core.

    If a solenoid draws 0.2 amps with 24 volts applied, it shows an impedance of 120 ohms.
     
  7. 1idejim

    1idejim LawnSite Fanatic
    Posts: 9,313

    No matter how i respond to your post it sounds like i am attacking you when i'm not.

    The answer to my question is "you can't know E or R without measuring them."

    You can shift focus by introducing phase angle, impedance and reactance and quoting Wikki or ABC or my main reference guide UGLY'S but my question was what are E and R? Without measuring them you don't know, you assume.

    When high or low current is at fault in a system, one can choose a path to troubleshoot by measuring I-E-R.

    High I should be blowing fuses and either R will measure low or Line/transformer output will measure extremely high.

    If the I is low or non-existent then the R will be very high, up to and including infinity.

    You can't have your cake and eat it too, an electrical circuit has to have E and R to produce useable I and these have to each be in porportion to each other.

    Your journey into Z (impedance) and X (reactance) as well as phasing (measured L-1 to ground and L-2 to ground) may be above the pay grade of most of this crowd (i'm no electrical engineer) but bottom line, not the answer.

    Solenoids are manufactured to specific resistance ranges to reduce current loads, and have been so since the 70s.

    The standard 20-60 ohms still works for the most part when diagnosing a solenoid and wire path.

    Below 8 still means there is a short somewhere and 180 still gives heed to poor splicing.

    When i see high amps and blown fuses i look at the resistance of the solenoid and the wire path along with the line and transformer output.

    Beats hell outta putting in higher amperage fuses.

    No harm, no foul :waving:
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  8. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,323

    cyclops speak with forked tongue :p

    here's a vector diagram of what goes on with solenoids - note that the resistance is only a small part of the actual operating impedance
    [​IMG]
     
  9. 1idejim

    1idejim LawnSite Fanatic
    Posts: 9,313

    This only is about Z in your mind Shoes. My point is that without measuring E, I and R you are guessing and troubleshooting via replacement.

    I made my point and that's what matters.

    :waving:
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  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,323

    The math, as displayed in the vector diagram, makes it clear that measured solenoid resistance is not so very material to actual performance in a system, since the inductive reactance in the scenario you supplied allows for operation without overload, even if you had measured zero ohms solenoid resistance.

    (of course, dead-shorted solenoids aren't going to generate the magnetic field that is responsible for inductive reactance, but a below-spec solenoid resistance, in combination with the usual amount of inductive reactance, would not prevent zone operation)
     

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