Switch from Rain bird to Rachio

post by tepkzo on Jul 20, 2021

The Rainbird was wired through the garage wall with a 24V AC transformer hidden in the wall somehow. It was wired with two bare wires to the controller. I’ve wired up the Rachio 3 with the transformer plugged into a long extension cord. Everything works fine. I want to put a female connector on the bare power wires so I could use the hidden transformer and get ride of the Rachio transformer connected to an extension cord. The switch does not seem like it should be any problem, but I just wanted to confirm before I made the switch. Thank you.

post by DLane on Jul 20, 2021

@tepkzo - I would find the Rainbird transformer and replace it with the Rachio one by cutting the Rachio cable and splicing it into the cord used to run to the Rainbird. If you have a garage door opener, check for a plug above the garage door opener to see if it has a transformer there for the Rainbird. I’ve seen that a few times.

I’m recommending the Rachio transformer to make sure it is sized correctly - Goldilocks not enough amperage and not too much amperage produced by the transformer.

post by jseymour on Jul 20, 2021

It would behoove you to find it. That is an unsafe condition.

Odds are the Rainbird used 24VAC, just as does the Rachio 3. Key words there are “odds are.” Have you put a meter on both to confirm?

Insufficient amperage: Yes. But, regardless of the mystery transformer’s capability, the R3 and connected solenoids will consume only as much current as they require. Too much voltage would be a possible concern, but too much current capability not.

post by DLane on Jul 20, 2021

@jseymour - I was concerned about too much current running through the Rachio board in a short circuit situation on a valve/wire. Normally, not a concern with having too much amperage/capacity - but as Rachio is all electric instead of mechanical the components might not handle the extra amperage in a short circuit condition. There are posts where people put the 24 VAC leads from an old transformer onto the 24 VAC ± Rachio leads and it burns out a component, so I think there are current limits in the design.

post by tmcgahey on Jul 20, 2021

Might sound silly, but are you sure that the Rain Bird was wired in with a transformer? Many controllers are wired to standard 110v and have a built in transformer.

Having a transformer hidden in the wall means that there is an outlet behind the wall as well, which is a HUGE no-no!

post by jseymour on Jul 20, 2021

Maybe there’s an outlet. Maybe not. There are doorbell transformers meant to be “plumbed” directly into J-boxes. Nonetheless: I don’t know what code is for such an installation, but I doubt “buried behind a wall” or “buried above a ceiling” (as the original owner of our home had done) is legitimate.

(Personally, electrical and building codes aside: I’d want to know where those wires went/came from. I don’t like mysteries where such things are concerned. Mysteries like that tend to have downsides.)

post by tmcgahey on Jul 20, 2021

Completely agree with you there. I hate not knowing things about my house. I had a light switch that took me 10 years to figure out what the heck it did…

Can’t say I’ve ever seen a sprinkler controller run on a 24v system like a doorbell (I’m pretty sure the amp draw for a controller might be too much, especially a smart controller), but anything is possible.

post by tepkzo on Jul 20, 2021

I did put a meter on and it was 24 v AC.

post by tepkzo on Jul 20, 2021

The wires coming into the Rainbird controller did check out as 24 V AC.

post by tmcgahey on Jul 21, 2021

How old was the Rain Bird? I guess it is possible that you have a 24v transformer plugged in somewhere. If you can find it and confirm the amperage, you can see if it is compatible with Rachio, but until then, I wouldn’t try connecting to it.

post by tepkzo on Jul 21, 2021

The unit dates from 2003. The voltage is 24, but I can’t find the transformer. I’ll keep the extension cord with the Rachio transformer to be safe. Thanks for all the suggestions.

post by GBNTX on Jul 26, 2021

FWIW, I made the same switch and I did use the 24vac leads from the Rainbird transformer on the 24v labeled connection to the Rachio. It has been working just fine. One thing all these responses failed to address in terms of the old transformer being able to supply enough current… that same transformer ran the sprinkler valves just fine which is where most of the current draw will come from. If you are only changing the controller, you really haven’t added any additional current requirements and may have, in fact, reduced it somewhat with newer, more efficient electronics in the Rachio controller.

Just my .02 worth.

post by jseymour on Jul 27, 2021

My issue was never the supply voltage and current capability. 24VAC is 24VAC and, as long as the old transformer has the current supply capability–a pretty safe bet considering it filled the same role: Have at it.

My concern with the OP’s situation is he’s got a transformer somewhere and has absolutely no idea where it is.

At its heart: An AC transformer is a pretty simple thing: Two coils of lacquered wire and an iron “core.” Random graphic from somewhere on the 'net:

There usually isn’t much that can, or does, go wrong with them. The key word here is “usually.” They can and do fail. And, while it’s exceedingly rare for small dry transformers to fail in such a manner so as to catch fire, it does happen.

Whomever “buried” that transformer behaved irresponsibly. Continuing to leave it buried is equally irresponsible.

post by LongIslandDad on Jul 27, 2021

If you do indeed have a 120vac outlet and a transformer “hidden” inside of a wall, you’ll want to rectify that ASAP. It’s against NEC and rightfully so as it creates potential disaster.

Convert it to an accessible outlet and then simply plug the Rachio transformer into it.

post by tepkzo on Jul 27, 2021

Thank you, very helpful comment.