Do most sprinkler controllers have short circuit protection?

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JimLS

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I have a diy sprinkler controller (opensprinkler) that is networked and has some nice features. One of the reasons for it is I have a lot of zones and this is easily expandable.

My question is about protection from shorted valves. This controller is weak in this area and I have several zone outputs that are bad. From what I have read it is not uncommon for a valve to fail with a short or low resistance and some controllers will report it.

Are most commercial controllers have some sort of short circuit protection so the controller isn't damaged by shorted valves?

How does this protection work? It seems some use more sophisticated means that just a fuse that opens.

The system has a 2A fuse in the 24VAC input. This powers the raspberry pi circuit board and the zone outputs. I separated the pi power so the fuse just feeds the zone outputs. A typical zone is about 0.22A so the fuse seems like overkill. I think a 1A should be sufficient.

A 2.2 ohm resistor is in series with each output but it doesn't limit the current to a reasonable value and burns up for shorts making a mess of the circuit board. I think they eliminated the resistors on later versions.
 

WorthFlorida

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Is the controller hand built or an ancient factory made one? Can you post a picture?

A shorted solenoid will rarely, if ever, cause an in line fuse to blow. Most newer controllers will indicate a short and not damage the controller. Just this week I fixed my neighbors irrigation by replacing a shorted solenoid. The landscape guys tried to fix it. The Rainbird ESP controller displayed an alarm for zone three and all the other zones continued to work. Since they didn't know anything about irrigation controllers they replaced the controller with a different Rainbird model, but this one would shut the entire controller down until the zone was removed from the program or the wire was disconnected. I know this since I was showing them how to troubleshoot. The controller was $110 at Lowe's, the solenoid was $11.

BTW, the shorted solenoid read 2-3 ohms and a good one was around 42 ohms. With an open solenoid, the controller cannot sense this and it will continue to run that zone though nothing happens. However, with a pump it will continue to run if you're using the MV connection to run the pump motor and all that pressure has no where to go.
 
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JimLS

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It isn't hand built or ancient. It's a open source (code and schematic is published) raspberry pi add on circuit board. Don't have a picture handy but here is a link. Sounds like I need to add a current limit to the outputs - that's something I can design pretty easily and put together and add but I was wanting to find out what recent commercial controllers did in this regard - thanks for the info.

https://opensprinkler.com/product/opensprinkler-pi/

The documentation is here:
https://github.com/rayshobby/opensprinkler

Some of the documentation is scattered a bit and some of the schematics aren't available as pdf but it is there if you dig a bit. If anyone is interested I can help point you to what I have been able to figure out.
 

JimLS

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One zone went bad and I have some extras so I moved it to another zone that was then damaged. What seems to be happening is that the coil is good when cold but shorts out after it has been on a while. It was loading down the 24VAC supply and only 16VAC at the zone output. But when I got to the zone valve about an hour later it had cooled and measured about 42 ohms.
 

WorthFlorida

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Small 24vac transformers are not regulated. You may measure up to 29vac with no load and as you've seen, 16vac under load.

It seems that this unit was one of the first WiFi's on the market. A year ago I upgraded my Rainbird ESP controller to the ESP-Me with the WiFi module. It was less than $200.
 

JimLS

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Small 24vac transformers are not regulated. You may measure up to 29vac with no load and as you've seen, 16vac under load.

It seems that this unit was one of the first WiFi's on the market. A year ago I upgraded my Rainbird ESP controller to the ESP-Me with the WiFi module. It was less than $200.

I agree it is unregulated so the voltage will vary a few volts. But 16VAC under load is way too low unless something is wrong. I measure about 27V unloaded and about 25 with one or two valves on. It was 16V because the valve was shorted and low resistance. Probably would have blown a fuse without the resistance of the very long wire run - about 500' one way.
 
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