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Multiple Zone Operation - "Relay Mode"

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5 comments

  • Avatar
    Istvan

    Hi Sebastian,

    So, if I understand correctly, you want to add a 24V relay coil on one of your RM's output and power some valves directly from your transformer through your Eltako relay. That seems like a logical solution, but the transformer you got with the RM is a 24V/750mA transformer. A valve consumes ~240mA. Even if you would wire the valves directly to the transformer (through your relay), the 750mA transformer wouldn't be able to provide enough power for more than one valve + master valve and RM internal electronics. Overloading the transformer could result in voltage drops which in turn can reset your RM.
    Of course, you could drive the whole thing with a stronger transformer but keep in mind that by adding a relay between the actual load (valves) your RM will have no idea about eventual overloads and shorts further down the lines of the relay. It will only see the 0.2W consumed by the relay, regardless of the current that goes through the relay contacts. I wouldn't encourage such use as it bypasses hardware protection and can lead to resets.

    The fuse is a 60V/750mA PTC.

    Istvan
    RainMachine Support

  • Avatar
    Sebastian

    Hi Istvan, 

    I am running the RM with a bigger transformer, as the one from the package is a US plug and I am in the EU.

    What I have in mind is: 

    - Use bigger transformer for supplying the RM only. (1A)

    - Use a dedicated transformer for the valves as required by the amount and consumption of the valves.

     

    This is not exactly my usecase, but would make the RM more flexible and useful for bigger installations.

  • Avatar
    Istvan

    Hello Sebastian,

    That can work, but should there be any trouble on the relay output, the relay will be on its own. A fuse for this auxiliary transformer is a must.
    Additionally, since your RM won't have any idea that there was a short on its relay driving output, it won't tell you to look into it. If you're willing to take this risk, the relay idea can work. 

    Istvan
    RainMachine Support

     

  • Avatar
    Ralph Becker-Szendy

    I'm in a similar situation: If the RainMachine could at least turn multiple outputs on at the same time at low current, I could then use relays to turn the valves on.  I have several zones where in normal operation, only one is on at a time (for normal irrigation), but in case of brush fire, many or all need to be turned on at the same time.  The power supply for the 24V AC system is not an issue: I'm actually using a 100VA industrial control transformer (it also powers the well and pump control, the water softener, and a few other random things), and that transformer already has multiple fused outputs.  Water supply is also not an issue, we have 3+1.5HP water pumps, not to mention the gas-powered water pumps that comes into action only in case of fire.

    Right now, those valves are wired via a small switch box, with manual toggle switches, which allow me to override the sprinkler controller in case of brush fire.  But that requires someone to physically walk into the equipment room.  I would much prefer to be able to do that remotely.  One option is to remove these zones from the RainMachine, and connect them to an Arduino or Raspberry Pi with a bank of reed relays on the output.  But at that point, why even bother owning a RainMachine, since an Arduino or Raspberry Pi can do simple irrigation control just as well (albeit with a much uglier UI and API).  A better solution would be to put a handful 24V AV relays into the box, use the RainMachine as the master controller (if only it could be taught to turn on multiple zones at once), and go to town.

    Here is a concrete proposal: For each zone, allow the user to configure what is connected to the output.  The default would be a single irrigation valve (about 250mA power consumption).  An alternative (only applies to output 1) is the master valve.  This setting is already supported in the user interface, but only applies to output one.  Introduce a new alternative setting, which is an output that uses an external relay.  I just looked it up for fun: a typical industrial control relay with 24V AC coil uses 80mA, so the RainMachine can definitely handle at least 3 of them on at the same time.

    I don't know at what current setting the "soft fuse" in the RainMachine trips (I know, it is not an actual fuse, but a monitored current limiter).  Clearly, it has to be significantly above 250mA, otherwise there would be nuisance trips.  I'm going to guess that it can easily handle two valves connected in parallel, perhaps even three (at which point, the 18VA = 750mA power supply becomes the limiting factor).  If that's true, another possible value of this setting would be to tell the RainMachine that a particular output has multiple valves.  Similarly, the RainMachine should be configurable to know if a high-current power supply is in use.

    The setting for multiple valves per output, and for a relay (negligible current use), and high-power 24V AC supply could be hidden in an "expert mode" of the UI, since most users don't need it, and shouldn't be confused by it.

    Then teach the software to allow multiple outputs to be on simultaneously, taking into account the current limitations, both of the power supply, what is connected to each output, and the known limit of the "soft fuse" in the RainMachine.  I know this is quite a bit of extra work (yes, I write software for a living, I know how hard it is), but as you can see, there are multiple requests for it.

  • Avatar
    Sebastian

    Hi Ralph, 

    thanks for the description of your use case. I gues that describes the "problem" better than my small installation.

    Best scenario would be a version of the RM with potential-free contacts instead of 24V switches. But I guess thats too much to hope for.

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