Multimeter question.

Discussion in 'Irrigation' started by jcom, Jul 10, 2005.

  1. jcom

    jcom LawnSite Senior Member
    Posts: 791

    I have a new customer that has been having solenoids go out on him. 4 in the last 9 mos. since installation. Installer will not return phone calls.

    Hunter system. SRV valves. Cable used appears to be phone or communications cable. Blue or green casing with very small wires inside.
    Suspecting the cable to be the problem, I checked for 24v outside. It is running about 26v. Cable is buried for about 30 feet out of the building.

    When checking for resistance, can I take off the valve wire at the controller and read through the solenoid or does it need to be isolated completely? I get a reading of 6 on the 10X scale with the solenoid still in the circuit. Checking between zone wire and common. If 6 is a good number, there would be high current going to the solenoid if my figuring is correct.

    Thanks in advance for the update and assist.

    John :rolleyes:
  2. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,708

    Are the solenoids themselves testing as bad? After you removed them? Their life shouldn't relate to the wiring used to connect them. (even if it is undersized) If you got a 60 ohm solenoid resistance reading, that would probably be acceptable. And you do want to remove the zone wire from the controller before you test, so there's no confusion. The actual AC solenoid resistance at 60 Hz will be greater than what you read with the multimeter. If that suspect cable contains stranded wire, you will want to replace it. If it's only 30 feet, I think I'd replace it in any event.
  3. jerryrwm

    jerryrwm LawnSite Bronze Member
    Posts: 1,274

    I would change the wiring especially since it sounds to be thermostat wire at best, and probably speaker wire. Use a minimum of 18ga. For 30' it won't take that long to rebury it.

    As for the solenoids - are they the old style Hunter solenoids that used to swell and break the case? The contractor may have had old stock in the truck and found a place to get rid of them. Take them to a Hunter distributor and have them check them out.

    As for measuring resistance to a solenoid, you are looking for a reading that is way out of range. Solenoids may have a resistance reading of 20 to 60 ohms depending on manufacturer, and the distance to the valve, and the size of wire used. What you are looking for is one that reads significantly higher or lower than the rest.

    I would check to see about the solenoids first. 4 in 9 months is a little excessive. Actually a lot excessive.

  4. jcom

    jcom LawnSite Senior Member
    Posts: 791

    Thanks for the help.

    I did have the wire off the controller but not separated from the solenoid. Measured between wire from controller and common.

    I have only replaced one solenoid as the installer replaced the others but apparently got tired of warranty work! I am trying to find the reason for all the failures in a short period of time and is the reason I suspected the cable.

    Cable is buried under a sidewalk as well. It is not stranded cable but conductors are very small. I think the small wire has too much resistance and hence would require more current than the solenoids are rated for. After many months of use, they just fail. Any help with this perception is appreciated.

    Thanks again,

  5. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,708

    Undersized wire is about as likely to cause solenoid failure as undersized pipe is to cause sprinkler head failure. Poor operation, yes. Failure, no. There are bad batches of stuff out there, solenoids included. I had some mysterious solenoid malfunctions on some Irritrol/Hardie/Richdel valves, but only on the anti-syphon ones. Turns out that there is a magnetic core pressed into the hollow tube of the solenoid, and there was an air space above it, into which water could somehow penetrate, and freeze, even after thorough winterizing. The result of the freezing was to push the core downward a bit, and the following spring, the solenoid plunger could not raise high enough to open the valve. Valves in underground boxes escaped freezing problems.

    As long as the smaller wire is intact, it is only a resistance, that would reduce the voltage seen by the solenoid. Since most solenoids have positive operation at 20 volts, you can afford to lose a bit (not that you want to) through the wiring. Remember that the manufacturers allow for 800 foot runs of 18 gauge wire to a solenoid.
  6. Critical Care

    Critical Care LawnSite Bronze Member
    Posts: 1,654

    If I were tackling this problem, and if this is just happening to one valve, one zone, one wire within the cable, then I’d test the non-operative solenoid with a different wire within the cable. You could even switch out the ground wire, if you suspect it – which could cause multiple zone failures.

    The resistance from a thirty foot run of 18 gauge solid copper should be negligible, unless if physical damage has occurred. You stated that you’re showing 26 volts, which is fine, but if for some reason the supplied current from the controller is not enough to latch and hold the solenoid then this voltage reading isn’t going to mean a whole lot. If there is a current leak through the wiring – such as a nick or cut in the insulation, or maybe some connections getting soaked or underwater, then you could show 26 volts but not have enough current to activate the solenoid. A different controller with perhaps a little more output current per zone possibly could keep things ticking, up to a point of course, and you'd never know that there was a problem.
  7. bicmudpuppy

    bicmudpuppy LawnSite Silver Member
    Posts: 2,781

    Does the "bad" solenoid still work if you take it to the controller and touch the solenoid wires directly to the common and station terminals? If it does, maybe the solenoid isn't bad, if it doesn't, then you need a new one. I still wouldn't blame a wire sizing problem for solenoid failure.
  8. jcom

    jcom LawnSite Senior Member
    Posts: 791

    Wire size can have a direct impact on solenoid life. If current is too high, it will burn out the solenoid. Unlike water and pipe size, which does not have a relationship with heat. If a sprinkler head does not have enough volume/pressure, it will not function properly, unlike an electrical solenoid which if not given enough volts/watts/ or high current will fail eventually.
    Some troubleshooting needs to be between the ears and not just on electrical hypothesis!

    Thanks all for the help as the problem is ongoing as the resistance is within specs. Four valves in one season is just not in my realm of normal. When I have it tracked down, I will let you know.

    John :waving:
  9. bicmudpuppy

    bicmudpuppy LawnSite Silver Member
    Posts: 2,781

    Just one other thought, this is a new account for you, correct? Was the controller left on and cycling last winter? You mentioned heat, and that reminded me of a few older systems that I have seen when the controller isn't turned off for the winter, the solenoids continue to run, but w/ no water flowing over the plunger, they over heat and are bad in the spring. WM solenoids are real good at this, and they become magnatized to the point that they will not release the plunger when the solenoid is turned back off. You can tap them slightly, and they reset. Sometimes the pressure of the next valve opening or closing will make the plunger fall and you don't even notice the zone is sticking for a long time. You didn't mention brand, there have been some bad runs of solenoids in the last few years too.
  10. jcom

    jcom LawnSite Senior Member
    Posts: 791

    This is a new account. I don't know if the controller was left on. Very possible knowing what I know now! That is the one logical cause for all the failures.

    The system is Hunter all the way to the valves and then Maxi Paws and 1804 for heads.

    Thanks for the tip.

    John :rolleyes:

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