Opensprinkler 3.0 DC w/ AC Valves

[totnik]

Hello All.. new to the forum so appreciate any and all input

Long story short, we live in the Dallas area and got hit with lightning. I suspect it actually hit nearby but came in through the sprinkler wiring. Our existing Hunter Hydrawise system caught on fire but we caught it in time. Not wanting to re-invest in that and to appeal to the tinkerer in me I decided to go with OS3.0 system (DC).

Once installed, about 9 out of the 20 zones did not work. Did some troubleshooting, 3 had burnt out solenoids (Hunter SRV/PGV 1″) and 6 have the line itself broken (sigh).
1) The contractor mentioned that by driving these valves via DC may shorten the lifespan and lead to more burnt out solenoids over time. Is this true? I did read the article on how this works and it makes sense but I figured I’d ask the community for empirical input.

2) Given the large lot size we’re on (2 Acres) with the controller sitting at the far corner and the valves themselves located by the sprinkler zones, would there be any loss of Voltage/Signal given the large length of wire between the controller and valve? AC travels better over long distances vs DC. Hence the question.

3) If the lines indeed are broken, it’s going to cost me about $2500 to re-do the entire wiring setup so I’m thinking if wirelessly activated valves exist in the market today that I could integrate into this setup.

Thank you for your input.

[Ray]

1) I don’t think so — your contractor may be referring to driving the solenoids with 24V DC, but OpenSprinkler DC is specifically designed to drive the solenoid with an impulse voltage to engage it and then use a low voltage (7.5V) to provide holding current. This amount of current is compatible with the amount of current running through the solenoid under AC. So I don’t believe it shortens the span. In addition, plenty of people in the open source community built controllers that drive the solenoids with 12VDC (without the impulse-holding mechanism that OpenSprinkler DC uses), and have been doing so for a long time. So overall I think the risk of lowering the solenoid’s life span is very very small.

2) The claim that ‘AC travels better than DC’ should be taken within context. It all boils down to ‘wire resistance’. Power is wasted on the copper wires as electricity travels through it. The power loss is basically square of current times the wire resistance (I^2 * R). So under the same amount of current, the power loss is the same, regardless of whether it’s running AC or DC. As I said above, DC OpenSprinkler achieves roughly the same solenoid current as in AC mode, so the power loss is similar too.

Where ‘AC travels better than DC’ comes in is the fact that it’s easy to step the voltage up and down with AC. To transmit the same amount of power, higher voltage means less current, and less current means less power loss. So AC wins because you can use transformer to step up the voltage at the transmitter side, which reduces the current being transferred, thus reducing the power loss. On the contrary, it’s not so easy to step up and down DC voltage. If you want to know more, you can read the story of the fights between Thomas Edison and Nikola Tesla, the famous war of DC vs. AC.

3) Not sure how far your solenoid is away from the main controller. If it’s within WiFi range, you could get another opensprinkler and sets it up as a remote controller listening to the master controller. Remote zone is a standard feature supported by OpenSprinkler firmware.

[totnik]

Ray.. Thank you for the answers. This puts my mind at ease. It didn’t even occur to me to use the remote zone feature. The entire yard is blanketed in WiFI so connectivity isn’t an issue. Will dig into that this weekend. Any suggestions as to how to power said remote zone/OS3.0? This is an off the cuff question if you had something top of mind but will research it further. Thanks again.

[Ray]

The controller needs to be powered by a power adapter, so if you don’t have a power outlet where the remote controller is to be installed, that can be tricky. One option is solar power — one of the reasons to go with DC-powered OpenSprinkler is if you need to power it off-grid. I’ve seen customers using solar power (usually with a backup battery) to power it. It can accept input voltage of 12VDC, which is what solar usually outputs. But I have no idea about the cost of it — installing a small solar panel should be relatively cheap, I just don’t have any specific number in mind.

[totnik]

Thanks Ray. That makes sense

[Author]

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