TECHNOLOGY
After checking the breaker, it’s time to move on to oth- er possibilities. If the clock isn’t working correctly, check the timing mechanism where you program in the start time. It’s possible that a rain sensor is keeping the clock from running, or there’s an issue with the motherboard or daughterboard for the two-wire path. Some systems have up to three boards, so it’s a matter of going step by step to see where the problem is. If you need to, remove a board and try again. If it blows a fuse, remove a board and try again until you find the one that’s causing the problem. Look at the number of volts coming out of the power
Wire
connections are such an integral part of making certain
that a two- wire system works correctly throughout, but it’s easy to forget how much they matter.
supply to the clock. If it’s not matching what’s listed in the product specifications, check the breaker or ground fault interrupter. If the transformer is warm to the touch, you know there’s power running to it. “You start out at the very beginning and just work your way down the list,” he says. “It’s a methodical process. Eliminate what it isn’t to discover what it is.” Break the system down into smaller parts to check through them individually without getting overwhelmed by the possi- bilities. Is the clock the problem? It could be the wiring in the field or potentially the decoder that’s at issue.
Tracking the problem
Once you’ve gotten a display, turn something in the sys- tem on, then run the diagnostics in the controller. “Every manufacturer’s two-wire product has a diag- nostic or some way to let the clock tell you what it thinks the problem is,” Borland says. “From there, you start working your way out.” If the diagnostic clock isn’t communicating with all of the stations, you’re likely not getting power coming out of the clock. Remove the two-wire path from the clock and ohm check it with a multimeter. “Te two-wire path should always be an open line,” he
says. “If you’re getting resistance, find the path going out of the clock. Tere should be a junction box right near the clock. Open it and remove all the wire connectors. Ohm check each of the wires and look for where the short is. Once you find it, that’s the path you’re after.” Finding where the short is in a two-wire path can seem like it could take forever, but Borland narrows the problem area in the distance down quickly by working in halves. Once you’ve found where the path leads, walk about half the distance to the very end of the line. Find the junction box there, remove the wire connections and check it again. Do not reconnect the wires at the clock, leave those open. If there’s a short halfway down the line, you can check to see whether it’s still further down or closer to the clock. Heading back toward the clock, Borland says to go half- way again, and do those checks again. Working like that, going halfway each time, you’ll find the problem quickly. Sometimes, a junction box has three or four pairs of
wires connected to it. Borland says to think of it as a major intersection. From there, to continue working in halves, you can look around to see where there are ad- ditional valves following those pairs of wires to make a guess as to where the line continues. “Because contrac- tors don’t like going all over the place, a straight line to
32 Irrigation & Lighting March 2023
those valves is pretty much the best direction you can go to continue checking,” he says. “Not always, but often. In parking lots or working around planters, you’ve got to just guess where the line went.”
Checking decoders
If you ohm check it all and don’t find resistance, connect it back to the clock. A unique thing about two-wire that makes it a little easier to troubleshoot is that it’s a single, solitary two-wire path that goes throughout all of the sta- tions. Tat means that if you turn power on, every decoder on the property should be getting current, says Borland. Hook up your clamp meter, check the red or white wire and then the black wire, and read the current draw. AC decoders draw on average about half to one milliamp per decoder while idle. While there’s a zone turned on, it can be about 150 milliamps to 200 milliamps total. If you’ve got 100 decoders, that’s about 50 milliamps to 100 mil- liamps, plus 150 to 200 for the solenoid, making 250 to 300 milliamps total. “Te key thing is not what the milliamp read is, per
se, but it’s more about the black and red wires reading the same number. You want to make sure the pair of wires have the same number on each wire,” Borland says. “Tat’s the key. Te majority of these systems should read in the range of 300 milliamps or less.” Do each wire individually. When doing a milliamp test, clamp around the wire.
One common mistake while taking these readings is not giving the meter enough time, Borland says. You want to measure the electron flow path going down that wire, so you put it around one of the wires and you count slowly to three. Ten read the meter. “We can be such an impatient bunch of people that we don’t give the meter a chance to settle down. If after three seconds it hasn’t settled down, you’ve got a different problem. Tat’s likely a decoder that’s failing.” From there, go out to the first box. Check each wire
individually, one by one. Clamp test each one and count to three. After each junction box, once you’ve checked it, there’s 0.5 or 1 milliamp that’s no longer in the system because you’ve gone past it. Te number should be getting smaller. Don’t forget to clamp check the surge device. Many manufacturers of two-wire paths have a surge device that you could connect to a two-wire path and connect it to a ground rod. It should have no current draw on it. “Just walk the property. Do some deep knee bends, get into the valve boxes, open them up. Clamp on each wire one at a time and look for the high current draw. Any idle decoder that is not running the solenoid that is reading more than 2 milliamps, that’s a bad decoder. If it’s run- ning a zone, 200 milliamps is legit. But if it’s reading a lot on there at a single decoder, that’s a problem,” he says. Taking each step in turn, you should be able to narrow down the problem area and make replacements as neces- sary, Borland says.
Kyle Brown is the editor-in-chief of Irrigation & Lighting magazine and can be reached at
kylebrown@irrigation.org.
irrigationandlighting.org
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