SpudFiles

So I'm thinking of using solenoid actuated sprinkler valves for a particular project in which the flexibility of electrical control outweighs valve performance considerations. Having always used blow gun pilots in the past, I have a couple questions:

1. I have read that the best way to power the solenoid is three 9-volt batteries in series. What kind of battery life can I expect (how many shots)?

2. Are there any pressure restrictions? i.e. is there some maximum pressure above which the solenoid can't handle it? I wouldn't be going above 100 psi.

Thanks

yeah there are pressure restrictions... sprinkler valves are indirect acting valves. I know that some all metal sprinkler valves use almost exactly the same solenoid design as the one used on DCVs. If you stay below 250 psi you should be fine...

If you find some diagrams of solenoids you can see that there are a few springs that keep the armature with a small rubber disk pressed against the sealing face. When you reach a given pressure the force acting on the disk overcomes that of the springs and the valve opens... So at a given pressure this kind of valve will open

some links
http://www.answers.com/topic/solenoid-valve


this one looks more like typical DCVs ->

From my testing, I could not make any type of enhancement determinations with using two or using three 9 volt batteries. Both setups opened the valve quickly and completely. Using only one 9 volt, however, it would only partially open. So, if you want, you can use two 9 volt batteries instead of three if you want. I would think, however, that three batteries would last a bit longer than the 2-battery setup.

Pressure restrictions on the solenoid are generally going to be the same for the sprinkler valve itself. I've successfully used them at 100 psi so there should be no problem.

does this project require the use of batteries for operation or can an AC power supply or an AC to DC power supply work?

i posted some info on sprinkler valves and battery operation before. I guess I'll have to make a Wiki entry on the electrical side or start a thread to make a sticky.

Due to inductance, an AC voltage applied to a coil will be much less than the same coil with DC voltage. In DC, the current is directly related to resistance in the Ohm's law formula.

In AC, the formula uses impedance. With an inductor (coil) the impedance is higher than just resistance.

Magnitisim is directly related to coil current.

Due to the low resistance of the coil, the same operating current can be created with much lower voltage.

From my measurements, a 9 Volt DC source will cause a higher current in a sprinkler valve than does 24 Volts AC.

Many gas appliances for mobile homes are designed to run on either 24 volts AC or 12 volts DC using the same coil.

My recommendation is to use 1 9 volt battery. It should fire just fine. With the lower voltage, the battery will last much longer as less current is used.

Edit; I found the link to the prior discussion with the measurements of the coil voltage and current with AC and DC power.

http://www.spudfiles.com/forums/questio ... 18083.html

It includes measuring the current of a running sprinkler system to compare AC current verses the DC voltage required to produce the same current.

My 3/4 inch sprinkler system uses 1/4 amp to operate the valves. I can get 1/4 amp with either 24 volts AC or about 6 volts DC.

In this photo the meter is bridging AC power from the AC transformer input to the sprinkler valve output bypassing the control so the meter reads the coil current.

My recommendation is to use 1 9 volt battery. It should fire just fine. With the lower voltage, the battery will last much longer as less current is used.

From my testing, the solenoid will open much slower and will not open fully when using only one battery. I've tested this in three different valves, getting the same results. Between using 2 and 3 batteries, I could not tell a difference between the two.

To add to what others have already said...

You can use an AC to DC converter (like a wall wart). Figure a fresh 9V battery sources about an amp (or a bit less). Two or three in series source about the same current. Any wall wart needs to be able to source at least an amp to be as good as the 9V batteries. A lot of cheapo wall warts are only rated to a couple hundred milliamps so read the label and make sure the wall wart has enough ooomph.

My experience using a pair of 9V in series is that the batteries last a very long time. They'll probably rot before they actually die.

If you are running off AC power, you can always use a AC transformer for a sprinkler system.. They have enough ooomph..