Rain Sensor Compatibility
The rain sensor feature should be capable of considering a megohm of resistance as equivalent to an open circuit.
This is a suggestion for improvement in a future firmware release. My 20-year old Hunter Mini-Clik rain sensor is not compatible with my new RainMachine Mini-8. The problem is that when the rain sensor is wet, the off state of the switch is not a completely open circuit and the RainMachine detects the switch as closed. The resistance in the off state is about 6 megohms when the switch is wet. Obviously this is a failure of the "splash resistant" specification of the Cherry switch in the rain sensor. After a few hours of exposure to hot direct sunlight, the switch provides a completely open circuit. Of course, by that time, the hygroscopic material has also dried, so the switch is in the closed position (except when manually being tested).
The RainMachine could easily be tolerant of that failure, since the closed state of the switch provides a circuit with only about 1 ohm of resistance. Detecting the difference between 1 ohm and a megohm on the rain sensor input should be easy. Of course, the only reason you even need a hardware rain sensor is to meet the letter of the (archaic) law in your community. Obviously, the RainMachine does not really need a physical rain sensor if it is using the Internet to estimate rainfall. So I feel no need to run out and spend $20 on a new rain sensor; and my town irrigation inspector (yes, I have one) will be satisfied just by seeing the old (non-functional) rain sensor in place and hooked up. He won't know it's not working and if I ignore it, neither will I; and the sprinklers will still not run when it's raining. But it would be nice if the hardware rain sensor feature worked with a slightly damp switch.
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Just an FYI, I also have one of the more 'electronic' rain sensors that when rain is sensed a high resistance is seen that effectively blocks current to the relays, Never an open circuit.
Anyway, I added a 24 VAC relay in series with my sensor and when rain is sensed, the current is reduced enough to turn the relay off then using the Normally Open relay contacts connected to the RainMachine rain sensor inputs, the rain sensor circuit works well. My relay has an LED in it and it quite bright when no water is in the sensor trough and dims considerably when water is present.
Anyway, this is a work around. Get a good relay if you try this as it will be On 99% of the time.
John
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Thanks, John for the great workaround idea. As for the relay being on 99% of the time, since my rain sensor has both normally open (NO) and normally closed (NC) outputs, I could rewire it to be NO in instead of NC and then the relay would be on only the 1% of the time when rain is sensed. I'm considering a Schrack PT270524 for the relay, since it seems to be available for as little as just $6.I just need to study the Schrack data sheet first to see how much current it will draw and if I can power it from the RainMachine's transformer. Also, having the relay being on only when rain is detected avoids the transformer having to power two irrigation valves (master and zone) and the relay at the same time.- Roy
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One thing I have now seen using a relay with one of the old school rain sensors that do not truly go open circuit, is relay chatter!
It seems that when the sensor probes are just barely touching the water in the collection tray or when rain drops splash the water in the tray when it is right at the probes, the resistance does not go high enough quick enough to open/de-energize the relay. So, it is right at that cusp of opening so a lot of chatter happens, (relay opening and closing very quickly) and I have gotten maybe 50+ notifications that rain has been detected.
I will rectify the AC to DC, get about a 5 volt 1 watt Zener, reverse biased and in series with a new 24 volt DC relay in hopes it will stop conducting quick enough to stop any chattering.
John
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