Connect with us

Rain Sensor Status

Discussion in 'Sensors and Actuators' started by chopnhack, Sep 9, 2014.

Scroll to continue with content
  1. chopnhack

    chopnhack

    1,573
    352
    Apr 28, 2014
    Thanks Kris, I appreciate the walkthrough. I am glad I didn't do more damage!! I was very surprised though when I plugged it in and saw the Red led come on, go off and as I was reaching to pull the adapter off the socket, a pop! The magic smoke was well contained inside the case, so much so that a few minutes later when I brought it inside, the rich aroma and dense white cloud was still lingering inside :oops:

    I didn't have the bridge rectifier's negative to common, I connected the 24VAC to the phase legs of the BR and then +/- ran through the circuit. I took the phase side of the rain sensor switch terminal and brought that in through the diode and capacitor and then to the 0v rail. See below. (C3 is what exploded in the previous picture).

    [​IMG]
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    Yeah, I guess C3 would have seen about 40V across it. If it was only rated for 10V that would explain why it turned itself inside out!

    Electrolytics can be pretty dangerous. A former co-worker of mine had a medium-sized one explode just seconds after he had stopped examining the board up close. If he had still had his face down there when it went, he could have been blinded.
     
    chopnhack likes this.
  3. chopnhack

    chopnhack

    1,573
    352
    Apr 28, 2014
    Wow, I would have never guessed that.... When I picked the part, I figured since it was on the 5v side of the regulator a 2:1 safety margin was adequate. When I checked the simulation and it was only about 2.7V I felt pretty comfortable. How did you come up with ~40V?
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    Have a look at this diagram of your whole system. I've shown the AC adapter that supplies 28.5V AC RMS to the irrigation controller and your circuit, and the irrigation controller with its row of connectors, and the rain sensor switch (in the closed position), and parts of your circuit, including the bridge rectifier at the input.
    270202 C3 overvoltage explanation.png

    Have a look at the sections I've highlighted in red and blue.

    The secondary of the AC adapter has 28.5V AC RMS across it, right? So that's about 40.3V peak. So at one peak of the mains cycle, the bottom end of the secondary is 40V positive with respect to the top end of the secondary.

    Current will flow along the red path, through D8, through C3, then back along the blue path, through one of the diodes in the bridge rectifier, and back to the top end of the secondary. The total drop in the red part of the circuit is about 0.7V (for D8) and the total drop in the blue circuit is about 0.7V (for the bridge diode). That leaves about (40.3 - 0.7 - 0.7) = 38.9V across C3. That's why it popcorned.

    The reason this didn't show up in your simulation is that you didn't include the external circuitry and current paths in your simulation. Your simulation was not complete.
     
    chopnhack likes this.
  5. chopnhack

    chopnhack

    1,573
    352
    Apr 28, 2014
    Wow!!! Totally missed that... Why would that have not shown on my meter when I actuated the switch? Was it too fast of a transient? Thanks for explaining that to me :)
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    Not sure. I didn't see exactly what you did.
     
    chopnhack likes this.
  7. chopnhack

    chopnhack

    1,573
    352
    Apr 28, 2014
    I had the leads of the DMM across the terminals where the rain switch is connected - RS and C. I will recheck this day after tomorrow, but that is how I came up with the numbers to design the circuit. Again, thanks for the explanations and the super simple design :)
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    Right. Well, you wouldn't see 40V across the rain sensor switch, whether it was closed or open. What you'll see across the switch depends on the characteristics of the input circuit in the irrigation controller - the part I marked "DETECTOR CCT". That's different from the voltage you'll see across C3.
     
    chopnhack likes this.
  9. chopnhack

    chopnhack

    1,573
    352
    Apr 28, 2014
    True, I didn't expect anything more than the 3VAC. I guess that it would have been safer with a 1/2 wave rectification, would not have had the potential to draw the negative cycle through the common. I have so much to learn yet!!
     
  10. chopnhack

    chopnhack

    1,573
    352
    Apr 28, 2014
    As a test, I tried the toner transfer method on a piece of galvanized sheet I had leftover from another project. Interesting results. A little touchup was needed in a spot or two, but encouraging. The paper I used was less than ideal, there was only one choice at Office Depot - double sided glossy cardstock. I can see why now they say the dextran coated paper works so well - the fibers from the paper sometimes pull up the toner. With the dextran powder coating the paper, the dextran dissolves in the water bath thus releasing perfectly.

    upload_2014-10-7_12-45-19.png
     
    Last edited: Oct 8, 2014
    KrisBlueNZ likes this.
  11. chopnhack

    chopnhack

    1,573
    352
    Apr 28, 2014
    Well.... we had limited success :(

    I populated the board, tested for shorts to ground before hooking it up to AC - all good. Powered on, green LED came on - all good. Climbed up on the roof and wet the sensor came back down expecting to see the red LED lit up - no good! Powered off and checked the RED LED1 with DMM - LED good. :confused:
    Here are some more data points I checked while troubleshooting. There was continuity on the normal closed leg pairs of the relay and non on the open leg pairs. No potential across the coil bothered me. 3k resistance across coil somewhat reassured me that the coil didn't blow out.
    As I went back over the circuit, I think I spotted a flaw. The switch in the center of the schematic shows a normally open switch, while the rain sensor on the roof is a normally closed switch! I wet the sensor and measured a resistance of 5M ohms, I think that confirms that its normally closed switch.

    Is there any work around that can be done since I already etched the board? I was thinking perhaps a transistor could help?
    Thanks in advance!

    upload_2014-10-12_15-18-48.png
    upload_2014-10-12_15-29-37.png

    upload_2014-10-12_15-20-52.png

    upload_2014-10-12_15-21-13.png
     

    Attached Files:

  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    The Rain-Clik information sheet is at http://www.hunternawadnianie.com.pl/sites/default/files/IC_RainClik_dom.pdf

    According to that sheet, the Rain-Clik provides a contact that is closed in dry weather, and open in wet weather. This contact can be connected to the sensor inputs on an irrigation controller, or simply wired in series with the irrigation valves, so that during wet weather, the valves cannot be activated by the irrigation controller.

    If you're not seeing any voltage across the relay coil, and LED2 is illuminating, that means that either there is a break in the wiring to the Rain-Clik, or the Rain-Clik has not been allowed to dry out for long enough for it to return to the closed state.

    The connection from the relay to the irrigation controller uses the relay's normally open contact. This is right, because the relay is supposed to "repeat" the input state. If the Rain-Clik contact is closed, the relay pulls in, and the NO contact is closed. So the output state from the relay is the same as the input state from the Rain-Clik.

    I think you just need to wait for the Rain-Clik to dry out. Then the relay will pull in, the LEDs will change over, and you will get a closed contact to the irrigation controller.
     
    chopnhack likes this.
  13. chopnhack

    chopnhack

    1,573
    352
    Apr 28, 2014
    I'm not sure, the switch was bone dry when I first tested it out - I was on the roof, had a good view of it and there has been no rain in the last few days ;-) I was even able to depress the button to actuate it and it clicked back into original place.

    I thought the schematic was drawn in the normal operation mode of dry with LED2 (green) being active when the rain switch is closed. The way the schematic is drawn shows the "wet" status with the rain switch open. I believe that this means I have the LED's in the wrong places as LED2 should really be Red while LED1 should be Green.

    I can jumper the rain switch positions on the board and see if the coil actuates.
     
  14. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    LED1 will light when it's dry, and LED2 will light when it's wet.

    The schematic shows the relay in its un-energised state. This corresponds to an open circuit at the sensor, which corresponds to a wet condition.

    Yes, try jumpering the rain switch, to simulate a dry condition.
     
    chopnhack likes this.
  15. chopnhack

    chopnhack

    1,573
    352
    Apr 28, 2014
    Thanks Kris, with any luck I can get back out there on tuesday :)

    I also realized that the LED I used was so damn bright, it will be a nuisance... I will have to order some diffused LED's to replace them. I assume the red will be just as bright. I can't move the physical locations of the LED's because they match up to corresponding windows in the housing. I will just drill some holes and jumper the positive traces.

    The real mystery is why there is no switching when wet? I did jumper the two nodes (between the rain clik's leads on the board) but nothing happened. I then probed and there was 37VDC between the two points... Strange behavior. The rain-clik is good, I tested the switch with its wiring after it was installed - it opened when wet. The high meg ohm readings I was getting was the meter registering my own resistance - I noticed that I was getting intermittent readings and my skin was touching the probe and copper! When I took myself out of the loop there was no continuity. The rain switch is currently in open status.
     
  16. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    Right. Actually there could be an issue with the Rain-Clik - it is specified for use with 24VAC. The documentation says that you must not use it with 110VAC, but it doesn't say anything about 24V DC. And it doesn't describe the electrical characteristics of the Rain-Clik's output.

    I have assumed that it is an isolated contact, like a switch. Presumably, some springy contacts that are pushed apart by the hygroscopic discs when they get wet. Clearly this switch can carry some significant current, because it's designed to be connected in series with the valves. But they operate at 24V AC, not DC.

    If it's just a switch contact, it will have no problem switching DC, as it does in that circuit. The difference between AC and DC, from a contact's point of view, is that with DC, it's easier to get arcing between the contacts as they open, especially with inductive loads. But there is a diode across the relay coil, which should prevent or greatly reduce this arcing. And in any case, the contact isn't even closing yet.

    So I doubt that switching DC instead of AC will be a problem. But it would be nice to know the exact characteristics and ratings of the switch inside the Rain-Clik.
     
    chopnhack likes this.
  17. chopnhack

    chopnhack

    1,573
    352
    Apr 28, 2014
    Indeed, but I doubt Hunter would provide any information to that end! Most companies don't support unauthorized utilization of their products. I can get a resistance value when it dries out (should have been dry already?). I will try and take a reading tomorrow morning.

    I think the arcing would be a longevity issue, not a non function issue.

    Agreed, the contact isn't closing yet, however, this morning before I wet it, it should have been closed/dry to start with!
     
  18. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    Right.
    Yeah, you said. Can you bring it inside and dry it with a heater?
     
    chopnhack likes this.
  19. chopnhack

    chopnhack

    1,573
    352
    Apr 28, 2014
    Negative! LOL
    It's mounted fairly high up with the wiring run through the eaves and then a crawl space - not impossible, but highly unlikely to be redone ;-)
    The high today was 96 deg and it was sunny. The position of the rain clik is on the southwest corner (not ideal per the manufacturer, but the only truly accessible location). I am having a hard time believing that device held onto the water that long. That is another one of the reasons I would like to have these LED's functioning - I wanted to monitor the drying time to better tailor a watering schedule.

    Thank you for thinking of all the possibilities. I could on tuesday take a hair dryer up the ladder! :D:p
     
    KrisBlueNZ likes this.
  20. chopnhack

    chopnhack

    1,573
    352
    Apr 28, 2014
    Sensor dry, contacts closed - green LED still on. 37VDC across coil of relay - relay still stuck in NC positions! Apparently the relay is dead. I am going to see if Digikey will replace it for me.

    Edit - Before I contact them I realized that if there is 37VDC across the terminals of the coil, doesnt that translate into 26vDC and exceed the the coils capacity since they are rated at 24vdc?
     
    Last edited: Oct 13, 2014
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Similar Threads
Loading...
Electronics Point Logo
Continue to site
Quote of the day

-