Solar Powered Solenoid Valve

I had posted on the previous forums and received a great deal of good advice which allowed me to take my project past proof of concept phase. At this point I'm actually planning to try and impliment what I've investigated.

Long story short I am using a circuit quite a bit like the one here. Only replace the motor with a solenoid valve to allow a few seconds of water flow upon command. (Which will have the ardunio controlling a component in the circuit to control when to allow the solenoid to open, but only when sufficient power is available.

Now my test of this circuit (proof of concept) worked wonderfully and I was actually able to run a high speed motor off the setup and it would run for several seconds before draining the capacitor. (4700uf)

Now here's the tricky part, I'm preparing to buy the final test parts. I know I will be getting a differen 1381 unit to correspond with the solenoid valve... there in comes the trick. On my last post someone had linked me a few solenoid valves but since then the "ideal" one has become a bad link. I'm only looking at pushing a little water at a time which will be gravity fed (I can provide pressure behind the valve to help "crack" it if gravity won't suffice) But basically I'm looking for a low voltage, cost effective valve I can use in my project.) If this test works out for the first length of the system as time goes on I'll wind up adding more and more to it.

(Project is "GOATEE" Garden Operations Automation Through Excessive Engineering) This segment detects moisture in the soil, compares against soil tempature, and then waters plants per need based around the ardunio board. So far I've got the watering well along the way (above) and my moisture sensor is working, but still a great deal of fine tuning to do before it is ready to run the show on determining when to/not to water the plants. I'm moving into my home in a few months and plan to setup the system with my garden as I build it :) Really enjoying this project. Any help you can provide in ways to improve the above, or pointers on a trust worthy source to get a reasonable valve would be wonderful!

(edit was ninja spelling fix)

I can provide pressure behind the valve to help "crack" it if gravity won't suffice) But basically I'm looking for a low voltage, cost effective valve I can use in my project

As long as you can provide the pressure then (in Aus anyway) these cheap solenoid valves are available in all irrigation and hardware stores.


what kind of volume are you going for? if you need a lot and can get back pressure to close them then the irrigation valves will be your best bet as you can get them for around $20 and they come in lots of sizes

if you don't need as much flow you could get a ice maker valve unit but some of them have 120v coils so make sure you get the right one

if you need something for low or no pressure water you may want to make something using a check valve and a servo motor or solenoid to open the flapper (just install the check valve backwards and drill a hole in the top plug to run your wire threw that will attach to the solenoid or servo) or you could do the same thing with a toilet tank flapper valve

well low pressure would be ideal, I'll look into the ice maker valves, those sound promising... Irrigation valves (looked at the store today) is a tad bit overkill and seems only ones I could find were 24v but take like .5 amps! to power... Thats a hefty bit of power, I'm trying to keep the power requirements a bit lower for practicallity purposes, of coarse if it comes to it I'll adjust my setup to get better recharge rates. (IE better solar panels)

worst case the check valve servo combo is an option, but I think I'd be happier with the ice maker valve.

Here are some you may like

3/4" Nylon Solenoid Valve 12v (3psi minimum inlet pressure) $18

12v Water Solenoid valve (smaller 0-25 psi) $8.50

1/2" Gravity Feed Electric Solenoid Valve (0 psi) $21

Well found wediggers, and cheap(ish) also. I'll save these pages for future reference. Thanks.


Thats exactly what I needed! From my math that should take about 4.8W to "crack" I'll have to see what kind of power I can push to see if my solar capcitor method is viable as is, or if I have to up my capacitance to make it practical.

(Only one's I've seen with better numbers used only .55W solenoid valves, but at 120$ a piece they kind of blow the project's budget out of the water)

I'm curious how many farad I'll need to keep that solenoid cracked long enough to get sufficient water. Ideally I used the gravity fed one, but I'll crunch numbers tomorrow letting my solar panel charge the capacitor until I see no further increase in voltage or amperage. (Still new to using capacitors for anything other then smoothing power)

RuralStorage Your cheap solenoid thing is something I have also pondered with, as I need something in the 25mm diameter range, and I refuse to pay the $120-150NZ they want.

For your application, how about a simple low pressure ballcock. I know they work at zero pressure as I have used them to feed a trough from a water tank sitting on the ground.

A small elevation will help, and each metre of elevation should give 1.4 psi (see The pressure is determined by the level of the water surface, so a tank with 2m of water in it has about 2.8 psi at the bottom.

If you have a limited water supply, you could use a seperate tank, which is only filled when the outlet ballcock is in the closed position.

A simple level detection on the side of the small tank (20 litres) would allow for registering the amount of liquid used over the period.

The other option to use a small tank, which is filled based on the amount required, and use a low flow discharge from it to the garden plants. As long as the water flows out, it doesn't matter if it takes several hours to empty. I have also seen the outlet for such "non eassentials" higher up on the water tank so that there is always water for the household.

Good luck Mark

There are numerous battery powered sprinker timers available here. Somewhere inside them is a valve that can be operated by just a few mA from a pair of AA batteries. Here's a non-specific example:

In season, I see these things in local discount shops for under $15. I would bet that they could be hacked to accept an open/close signal from an Arduino.

Thanks for both the above information.

I saw a few very cheap garden automation kits that had inline valves of some kind running off a 3.5mm stereo wire hooked up to it's timer... I know I also read about people hacking them for the ardunio (think they said it was 20v, but never got an answer on the amperage, running off batteries it has to be a trivial amount or it's bury the batteries in minues.)

I'm trying to come up with the circuit I need to accomplish my task (practical or otherwise) then adapt from there.

Okay trying to run off what I learned in college like 7 years ago, plus formulas I've dug out from various places on the net (so pardon me if my math is astronomically wrong.)

Granted this isn't practical for my application, I'm just trying to confirm my math...

So here's the circuit in my mind (an example not the one I plan to impliment) I run the solar panel through 10 x 25v 1000uF capacitors in parellel, once fully charged I begin discharging with a resistance of 55 Ohms into my 12v 400mA solenoid valve. This would in theory run the solenoid for roughly .55 seconds before the capacitor's output would no longer be sufficient to run the solenoid if it requires the full 12v 400mA to remain open... correct?

(I'm trying to confirm my fundamanetal understanding of capacitors) Which then If my understanding is correct the way to increase time the solenoid would remain open I'd need to increase the capacitance by adding either larger (in capacitance) capacitors AND/OR more capacitors in parrellel AND/OR use capacitors of a higher voltage with a higher resistance to the solenoid valve AND/OR use a solenoid valve with lower power consumption?

I could be horribly off there which is why I'm asking.

More then likely these battery powered water valves are latching valves where the electronics only has to momentarly pulse the valve open or closed, so as to keep continous current consumption as low as possible.


Rotrlefty The one battery powered timer I saw, used a tiny DC motor, and a few cogs to gear it down. The result pressed on a diapram, which allowed flow. it was designed for a pressurised supply, and had quite a restriction.

I have also seen some hydraulics, where they control a very small feed, which then opens the main valve. This system also requires a pressure to work.

I'm picking that RualStorage needs to look at a much lower power consumption for the operating device. You will also need to watch how much leakage your capacitors have. More capacitance equals longer run time, but also longer charge time. It may be better to actually use the solar to charge a battery, which you then use to power the operating device. You can step the voltage up or I do know that Dick Smith have 12v 1.5w solar panels for $39 NZD, which is pretty reasonable.

Cheers Mark

Yeah, I'm fooling with this now. my solar panel should pull 12v (I need to confirm once we actualy have a sunny day here... whomever called Florida the sunshine state was a liar!)

Anyways, I think I've got my circuit figured out saving if I add more capacitors. I realize the charge time will increase, and though I've done the math there's a ton of "if"s in there so I'm going to actually get everything working with the current circuit see how long it takes and go from there. (I had to laugh I realized the capacitor I purchased originally was designed to hold 4700 uF at 35V... thats a heck of alot higher a voltage then I need...)

But yeah once it's sunny we'll get some raw numbers and I can assess my panel to capacitor ratio from there.