External relay for master valve and pumps

Sorry if this is a duplicate. I searched around and found some similar stuff but not an exact match. My master valve and well pump setup are overly complex in that there are two different valves and a pump relay that all have to turn on. I currently have a “commercial unit” that can handle the current requirements but I’m concerned that my newly purchased Rachio will be right at the limit once a zone valve is added in. Are there any suggestions for an external relay and transformer than I can use to power all the stuff needed for my master valve so that the Rachio only needs to power a single relay for the master valve zone? Thanks!

@jfmoore75 - without knowing the equipment’s power requirements it would be hard to make a recommendation. There are several NO SPST 24 VAC relays with small coil amperage usage that could be closed by Rachio to provide power to the other devices. If the other devices don’t share common wires with the zone valves, it could be as simple as powering them from another transformer and having the relay switch the current on and off. I think Rachio is targeting a maximum of 350mA of load at one time (pump start relay or master valve and two zone valves when the reduce water hammer option is enabled). There are some pump start relays that pull too much power and will result in Rachio issuing a wiring fault warning, the solution there has been to find the special pump start relays that pull a low amperage on the signalling side and use those instead.

Pictures and equipment listing (models) would help confirm.

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@DLane - thanks for the reply. One of the valves is a Weathermatic Silver Bullet and the other is a standard residential valve (pictured). I’m not sure about the relay (also pictured) specs as I don’t see any visible writing on it. I only have a DMM so it would be difficult to measure the turn-on current but I could measure steady state current if that would be useful. I think the current draw is under 1 A but it’s probably good to check. The stuff on the master valve zone is isolated to that zone so there’s no shared wiring to other zones (other than the common wire).



@jfmoore75 -

I might wire in an additional power supply like this one ->


through a NO SPST 24 VAC relay like this one ->

Where the Rachio Master Valve/Pump Start line is connected to the coil of the relay.

I think if the common wire is shared one may want to use an isolator to connect the common wire between the two power supplies (I believe Rachio recommends this). Make sure the wire carrying the current from the external transformer is wired through the relay. If the common wires from the pump relay and the master valves were separate then I’d just wire them back to the external power supply, this may be possible if there is a spare wire in the field wire that could be used as a second common.

@DLane, thank you so much! I know I could get a Mouser or Digikey catalog and start to look things up, but it’s really helpful to have people with experience recommended parts known to work well with sprinkler equipment. There’re so many choices that it’s easy to be overwhelmed or choose the wrong part with some subtle difference.

To confirm, are the drawings below the connectivity you are describing? The isolator case is a bit complicated since both power sources are on simultaneously and I wanted to make sure the current is coming from the external power supply. I think the common wire for my master valves and pump relay is the only common wire in that box so I can directly connect it to the power supply and not have to worry about a shared common with the Rachio. If I’m mistaken and the master valve box isn’t wired straight back to the controller, and it shares a common with some zones is this the isolator that you’d recommend?


Thanks again!

@jfmoore75 -

  1. Yes, that is the isolator that Rachio has recommended in this article (I’m treating the second power supply as an additional controller) ->
  1. Don’t give me too much credit. I have recommended NO SPST and SPDT relays to solve other wiring issues in the past. I just ran a new Amazon search. I believe that is the brand that I’ve found before. The things to consider are 24 VAC coil, low mA coil load and contacts that are rated for the load (with 24 VAC load, it shouldn’t be a problem as most of them are 120 or 220 VAC).

  2. Yes, those are the wiring schematics that I was envisioning.

Let’s hope for the independent common situation as that is the cleanest. I’ve seen other posts where someone with more electrical savvy than me says that a common can be shared if that is the only wire shared. I just saw National Electrical Code and went the other way. I can see where it is way too easy to connect one side’s hot to the other side’s neutral or having the two power supplies be on different phases of the electrical panel, resulting in fun when if the hots are connected.

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@DLane thanks again! That article was my inspiration for the wiring diagrams. I also made the assumption that the extra power supply is a 2nd controller. I feel better with the isolator if it is needed. I think connecting two grounds together is okay if they are truly the same potential. With the AC -> DC transformers being in two different boxes I think it’s possible for the “ground” in each to float which would cause current to flow between them and that’s bad. There’s probably something creative I could do to tie the transformer ground references together but I think the isolator solves it for me and doesn’t require as much though (only $$).

@jfmoore75 - Those are both AC -> AC transformers. While there are some DC latching solenoids, most sprinkler systems use 24 VAC solenoids.

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Oh, yeah, duh. I knew but had the wrong picture in my head. Thanks! :slight_smile:

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