Arduino Uno two step solenoid control

[payty]

Hi,

I am designing an automated irrigation system using Arduino Uno.

The Arduino is controlling a relay board that switches on and off the solenoid water valve which takes around 1.5 amps/9-12V to trigger.

The thing is that the solenoid of the water valve heats a lot if powered with full voltage.
But after triggering, a very small voltage/current is required in order to keep it open (2V/500mA)

So far, the schematic is the one below which works great except that I cannot keep the valve open for a long time because of heat.

What would be a good way of a two stage power circuit of the solenoid?
I need a high power stage that delivers 9v to the solenoid and after 500ms to drop to 2V.

I was thinking of some sort of PWM-> DAC that triggers a high power transistor, but I only have medium electronics knowledge and I do not know how to do that.

Another option -> would it be a good choice if I use a step down converter and control it somehow to drop the voltage from 9V to 2V using the Arduino?

[Paul_KD7HB]

@payty

I cannot keep the valve open for a long time because of heat.

Please explain. Is this solenoid that you made or is this a commercial unit? If commercial, then heat is not a problem if the water remains in the solenoid, it is water cooled.

[TomGeorge]

Hi,
Can you please post link to specs/data of the solenoid valve?
I am aware that there are these type of valves that have a high activation current and low hold current to save battery or power supply load.

A simple solution is two relays, one with current limit resistor in series with the load.

Tom...

[payty]

The valve description is in the link below

CEME | Solenoid valves for industry | 8413

Meanwhile I have managed to modify the schematic (see below).

The code is like this:

I activate PIN8
Delay 2000
Deactivate PIN8
Activate PIN9
Wait for another specified amount of time (adjustable via interface).

Basically I activate pin8 which drives the solenoid at full power and then switch to the low power stage that goes through the buck converter.

So far the tests are ok, but I have tested it only a few times (max 20 open-close cycles)

Do you think this design is safe? It should be powered by a car battery and left without any surveillance.

The irrigation system will be used in a vegetables garden.

[Paul_KD7HB]

@payty

It should be powered by a car battery and left without any surveillance.

Then you definitely need a fuse right at one battery connection.

[Wawa]

The text says it's a solenoid, but the link says it's a servo.
So what is it.

Power to a solenoid can be controlled with PWM.
First circuit here.
Leo..

[TomGeorge]

Hi,
That site doesn't know the difference between a solenoid pump and a solenoid valve.

@payty that "valve" is designed for low duty operation in a COFFEE MACHINE.

I would suggest you got to a garden or DIY site and look for the valves that they use in automated gardening applications.

Google;

garden solenoid valves

You will find more suitable valves for your application.

Please post a complete circuit diagram, where is the valve?
Where is the battery?

Tom...

[clintux]

Hi payty. The valve you have linked to looks like a standard industrial solenoid actuated globe valve. I think the term servo actuated is translation error. If you have a 12v coil version it is designed to have 12v applied to it continuously. Some of them do run a bit warm and yours is dissipating 21 watts so it will. If you do not apply full voltage to the coil the plunger may not fully pull in and this will cause it to draw more current and run hotter, possibly to the point of failure.
As said above irrigation solenoids from the hardware or garden shop are suitable and will be cheaper that industrial ones. One point about standard garden solenoid valves is that they usually have a minimum working pressure before they will actuate therefore they are not suitable for irrigating from a tank but need some sort of mains pressure. The one you have is however, as it has a minimum working pressure of 0 bar. There is a type of irrigation solenoid that has a 9v dc pulse coil. these need a 9v pulse to open then another pulse to close again. They are designed for low power applications to run off a 9v battery. One more point about solenoid coils, AC and DC ones are different and not interchangeable. I have found however that in practive a 24vAC coil works quite fine on 12vDC with the ones I have. (standard Hunter or Toro valves) which I think have an 8 watt coil.