Setting up comprehensive irrigation system is not easy and could be pretty expensive – you need to dig trenches and run water pipes, run irrigation cables and install control valves. It is not cheap even for a relatively short runs, but when you need to water sections of the property that are 200-300-400 feet away it could become really expensive.
I have a small-size regular irrigation system at my property that covers area near the house – 4 zones with a common timer, however this system is not enough. I wanted to expand the system to add more zones with drip irrigation and few sprinklers, but it would be fairly complicated and expensive – need to dig trenches, run pipes etc. As many others I went with a simplest option and just run few good quality garden hoses to connect drip irrigation sections and sprinklers, and setup Orbit battery-operated timer that connects to a regular garden hose.
The Orbit timer I used is a four-channel model – one timer controls 4 valves, all connected to a regular garden hose. This allows me to run 4 additional irrigation zones using one Orbit timer.
Over time my irrigation system grew in size, and I added few more sections with additional battery-operated Orbit timers, all connected with garden hoses.
This setup works surprisingly well – I’m using it for over 9 years now and it proved to be quite effective. Upfront costs are fairly low – 4 valves + timer + 4-way water splitter costs under $75 (in the local Home Depot), plus some money for good quality garden hoses, plus drip irrigation part and sprinklers. Running costs are also fairly low – every year I need to fix few cracked drip irrigation emitters, sometimes need to change a valve or two, plus hoses eventually wear out – although several of the hoses I bought 9 years ago are still working fine. All-up it turned out to be fairly good and cost-effective way to do watering without breaking the bank.
The only significant problem I noticed over the years is the inconvenience of setting and changing irrigation schedules – since the schedule is individually set on each 4-channel irrigation controller I must walk over to each controller to program it, I must ensure that the clock on each controller is set correctly, and that irrigation schedules don’t overlap – since running more than one zone (set of sprinklers) at a time will not work – not enough water flow.
Also I cannot really change my irrigation schedule depending on weather – it will be too cumbersome to adjust the watering schedule across multiple timers, so usually I don’t bother changing it much – which leads to overwatering and under-watering.
While walking around programming my irrigation controllers I was thinking – wouldn’t it be great if I can program all schedules centrally, using common irrigation timer?
I already have regular multi-channel watering timer (the one that drives 4 zones near the house), it will be great if I can connect all my irrigation valves to it and just program it all from one place. It would also allow me to attach rain sensor and/or use other advanced options for automatically adjusting watering times based on weather.
This is essentially what you get with a regular fully wired irrigation system – all valves are controlled from the central timer, lots of advanced options and flexibility etc. However I don’t want to spend big on digging trenches and installing full-blown irrigation system.
Voltage Converter Option
In theory it is possible to connect all my irrigation setup to a central timer if I install blocks of regular 24VAC control valves but connect them to a regular irrigation hoses. I looked into this option, but it becomes complicated and cumbersome – regular 24VAC valves are designed for plastic ¾” or 1” pipe connectors, and I will have to install size and thread converters for every connection. Also regular 24VAC valves are designed for underground installation and are relatively big/tall, so I will have to dig holes to install blocks of valves underground to hide them out of sight. Plus I will have to buy all new valves – while I already have Orbit battery-operated valves installed and running.
Another option is to somehow connect these Orbit 91592 valves to a regular 24VAC irrigation timer – in this case I can use all the existing valves and water distribution system I have in place, and can just run irrigation cable from the central timer to these valves. This is the option I ended up implementing.
Orbit 91592 Valve
The Orbit 91592 Valve used with these battery-operated timers is a relatively simple thing – it has two wires and it is operated by DC pulse. This is a latching type of valve – voltage pulse opens it, and opposite polarity pulse closes the valve. Unlike regular 24VAC irrigation valve no current is required to keep the valve in open position.
I found some information on voltage and DC pulse characteristics for this valve on the internet, I can recommend this excellent blog: http://rayshobby.blogspot.com/2010/06/minty-water-valve-controller.html
Essentially the valve is operated by discharging 2200uF capacitor, charged to 24V. Positive pulse opens the valve, negative pulse closes the valve. Ray (in the article linked above) wanted to control this valve using Arduino MCU running off a battery, and he put together a special circuit for it with step-up voltage converter to get 24V while running on battery, H-bridge etc. My problem is a lot simpler and somewhat different, since I would like to connect this valve to a regular 24VAC irrigation timer that supplies 24VAC to each channel when it wants to open the valve, and removes the voltage to close the valve.
After thinking through it I came up with a simple “low tech” way of doing it – using relay.
The relay is an AC 24V relay – it is directly connected to the irrigation timer. When the relay is triggered, the valve is connected to the 24V DC via capacitor C1, this generates current pulse of charging the capacitor, and this pulse opens the valve. While the relay is energized the capacitor is connected to 24V DC via the irrigation valve and is kept charged. When the relay is turned off, the same capacitor is connected to the ground and discharges through the irrigation valve creating negative voltage pulse, closing the valve.
This circuit is amazingly simple, but effective. It is cheap, easy to put together, and it is also inherently safe with regards to turning off water if power is lost or the irrigation timer fails.
This is actually pretty important – I need to make sure that the water will not be left running if power is lost or something else happens with the control wire/timer. Regular 24VAC irrigation valves don’t have this problem because as soon as the control current disappears the valve closes, but Orbit DC valves are of a latching type and they will stay open until the closing pulse is delivered. The circuit above solves this problem by automatically generating this closing DC pulse as soon as control voltage is removed, mimicking behavior of a regular 24VAC irrigation valve.
The 24V DC power required for this circuit can be readily obtained from the 24VAC available at the irrigation timer using simple rectifier. I also added voltage step-down circuit to limit the voltage to 24V.
R1 helps to limit maximum current via LM7824, also it helps to make the current pulse wider. Because current goes through the system only for a brief moment when capacitors are charged and the rest of the time current is zero, no heat sink is required.
I assembled a four-channel version of this circuit in a suitable weatherproof box installed near the irrigation valves. Because on the valve side opening/closing current can be quite substantial (although short), it is preferable to limit the wire length between the voltage converter and the valve. Because of that I mounted the voltage converter closer to the valve rather than on the timer side of the cable. Wire length of 15 feet between the converter and the valve seems to work fine, but I would not want to increase it too much.
The cable between the timer and the converter can be as long as required, the system is actually pretty tolerant to the voltage drop and long cable on that leg because 24VAC relays consume less current than a regular irrigation valve and are tolerant to the long cable resistance. Actual irrigation valves in this design are running off stabilized 24V voltage (and mostly off capacitors), and there is no problem with long cable run from the power source (24VAC).
I’m planning to assemble few more of these converter boxes to replace battery operated timers I have.