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: 46,987

    The math was supplied beforehand. ~ 30-ohm solenoid. ~ 24 volts AC applied. ~ 0.2 amps measured current.

    My diagram connects the dots, and shows that it is the inductive reactance of the solenoid that is chiefly responsible for a solenoid's impedance.
     
  2. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,298

    ..................

     
  3. Mike Leary

    Mike Leary LawnSite Fanatic
    Posts: 21,786

    Can we all go back to work now? :dizzy:
     
  4. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 46,987

    I dunno, I'm all eager to learn why I should give a rip about magnetic forces.

    What I provided shows why you can measure a DC resistance that is well below what you expect, but still the zone operates without incident.
     
  5. gdeangel

    gdeangel LawnSite Member
    Posts: 36

    I have been reading along quietly, since I thought the panel reset had fixed the problem, but yesterday I went out and zone 2 (which is the one that had been "stuck" open in the fall) was running at the same time as zone 3.

    I decided to retest the transformer from the other advice I got earlier... (it was 29V red to red, and 12 v red to green last time) ... and anyway, it fried the fuse in my meter. So that put the kabash on trying to test anything else.

    But I was curious, because when I read all this stuff about solenoids and resistance changing under load, it seems that one thing I had always thought, that if the magnet can't pop open, then the things will get hot, just might be right. Because when it hasn't popped open, then resistance might stay lower, and too much current flows. I don't know... just tossing it out there. I actually did take a class once on electronics - just passed by skin of my teeth... ah, this discussion brings back memories.

    So I'm going to put in an SMT... which brings up another question: what's the difference between the SMT and the SMTe? Am I going to be revisiting these firmware bugs with either one of them?
     
  6. 1idejim

    1idejim LawnSite Fanatic
    Posts: 9,122

    only 1 leg will show a measurement to ground. that is the potential difference and should be around 1.2vac @ 120 vac line pwr.
    Posted via Mobile Device
     
  7. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,298

    Model 1 vs Model 2, and what firmware bugs?
     
  8. gdeangel

    gdeangel LawnSite Member
    Posts: 36


    Well that's interesting because I took the transformer with me, and tested it at home. I have 1.2 VAC on one leg vs. the green ground wire like you said but from the other leg to the ground wire it is definitely still reading more like 20VAC, and between the two orange wires, it is 29VAC. Don't know what that means, but the back panel says "24V", so I'd expect 24V between the two orange wires...no?
     
  9. 1idejim

    1idejim LawnSite Fanatic
    Posts: 9,122

    line power and transformer coils determine the low voltage output.
    Posted via Mobile Device
     
  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 46,987

    the 24 VAC transformer will always show 29 - 30 volts when you measure it, because it isn't running under the full load the transformer is rated for - load it down, and the voltage drops (and the solenoids aren't a full load, so actually seeing just 24 volts is unlikely to happen)
     

Share This Page