After a bit of googling, the water-passing solenoids I can find are either way too expensive, need way too much current, or they're way too small.
If you browse a basic solenoid supplier site, you find solenoids in the $200-$400 range each. Not going there.
I found an eBay vendor called valves4projects which looks very promising to hobby types. I sourced a couple samples from them, and I will finish my tests with them once I get the power/arduino control worked out. They're 12VDC which I can manage, and 0.6A draw to hold them open, which will add up quickly if I want to manage more than two or three of them. They're just about the right size (almost garden hose capacity). The durability and cycle speed are still to be determined.
So I did some other searching. I found a number of medical fluid dispensing solutions. A nice example is linked below: 5VDC and you only need to pulse the current to switch from open to closed, or closed to open. Reliability and speed are probably excellent. This would be great, except the size is a bit too small, and since it is part of the medical equipment industry, I expect quite expensive. They ignored my query emails.
Anyone here have a middle ground? Something I can switch fast and often, is inexpensive enough to buy a dozen, and pours a respectable amount of water (drinking fountain to garden hose range) at low pressure.
You can get sprinkler system solenoids at the local BORG (home center) that operate on 24VAC for about US$20 each, IIRC. The 24VAC transformer should be nearby.
You'd have to switch AC current with the arduino, but that's doable, and in exchange you get a reasonably cheap and ready supply of valves.
kg4wsv - thanks for the idea. That is just the right price. (I even found some down in the $10 range.)
I did find a few mentions of these types of lawn irrigation devices, but I can't seem to find specific ratings on those solenoids themselves (how much current, whether they need current all the time, etc.) or on the valve (how much water pressure minimum, maximum, etc.). For the record, I'll be dropping water from a shallow reservoir so nearly-zero minimum pressure required is better.
I also have looked at websites about fridge water-in-the-door solenoids, and tried to find the units used in cars for windshield fluid. Half of the sites about solenoids are patent paperwork, the other half are how-to-diagnose-problems forums that don't address the electrical specs.
As I already got a 12V 6A supply, I'm hoping not to find yet another power source, but if I have to, I have to. Got a circuit handy for switching AC from 3.3VDC or 5VDC Arduino outputs? No mechanical relays?
If you don't want to use relays, a solid state relay (SSR) would work, or at loads as low as this a discrete TRIAC would probably be the switching device of choice. I'm pretty sure the sprinkler controller I've seen uses TO220 sized TRIACs for switching the AC side. The conformal coating was such that I couldn't read any part numbers.
I googled a spec sheet that says 20 to 80 PSI pressure range, 0.3A inrush/0.2A hold current at 24VAC. I would guess this to be pretty typical.
If you're operating with effectively no pressure (i.e. gravity flow) a simpler valve such as the refrigerator or washing machine type may be more appropriate, as I think these are direct acting rather than a diaphragm type like the sprinkler valves. They'll typically operate on 120VAC; you'll switch them with an appropriately rated relay, SSR, or TRIAC.
The only windshield wiper systems I'm aware of (which is a very short list) are pumps, not solenoids, as they're simply pumping from a reservoir that's lower than the outlet.
Typically the garden sprinkler solenoids are 24V AC, but they work just as well with DC.
huh? You sure about that?
I haven't tries the solenoids, but I got a DC relay by mistake once and hooked it up to 24VAC - made a heckuva racket until I got the power killed. Most definitely was not interchangeable...
The instruction sheet that came with mine stated it needed 24V AC, but I use with my air cannon where the power comes from 3 x 9V batteries.
I can understand ones designed for DC not working with AC like yours - the power is changing direction 50/60 timies per second - the solenoid would be flapping about when it's not designed to. The ones designed for AC though I guess must just fire and hold when they get the non-osciallating DC
I'll swing by Home Depot in a couple days, see what they have on the shelf. If I like it, I can source them cheaper elsewhere, but if I don't, it's easy to return.
Regular 24V irrigation valves are pretty power hungry, especially since they need power the whole time they're on. I suspect that if operated on DC, they might eventually have problems with magnetization of the solenoid plunger. This depends on how they use them, of course. In an air cannon where the solenoid is triggered for a second or two "occasionally", it would be a lot less of a problem than in a real irrigation system when the solenoids remain activated for hours per week.
I have some battery-operated sprinkler timers that are pretty neat. They appear to use a valve that operates on short pulses of about 20V for both turning them on AND off. The circuitry contains a boost circuit that builds up a suitable charge on a cap and then zaps the valve; a set of 4 AA batteries lasts about a year, which is quite good.
Here's a link to one of the valves: http://www.unifireusa.com/retail1/item.php?c1=Orbit&vn=89334&grf=orbit&nameIT=Complete%20Automatic%20Yard&blkNO=1403-8368
It might take a bit of experimenting to figure out which leads are which; documentation seems to non-existant!
westfw, that looks like "best of breed" of the suggestions so far, but if it requires a capacitor to charge up, I worry it won't be able to cycle fast enough. I will have to look into the best way to MAKE a 20V pulse, then I could try a little program to give shorter and shorter times between pulses to see when it stops toggling reliably.
If you have 20V present (or whatever it actually takes), you probably don't need the cap any more. I was just impressed that the controller MADE 20V rather than using some sort of low-voltage valve.
You never did say what you were making. Most "irrigation" valves turn on and off rather slowly, and wouldn't be suitable for "artistic water shows" and such. You might want to look at pumps instead; I've seen automotive windshield-wiper pumps on the surplus market for not too much... http://www.sciplus.com/singleItem.cfm/terms/14315
i know there are some 30-50 dollar all inclusive watering valves. that means diplay, controller, some buttons and the solenoid in one "box" they run on regular AA or AAA batteries, not sure, but i guess if you had to change the batteries every week they would not sell them for too long.
so there must be better valves than the 24 volt ac ones that use up to 20 amps while they hold the valve open.
maybe one should purchase one of those and open it so see the valve. but a bit costly for me right now.
i investigated a bit into water solenoids and here is what i found out:
most solenoids run on 24V AC and DC. The AC currents gets converted to DC inside the solenoid to drive the magnet. A electrical magnet can only pull in one direction under DC current afaik. AC current is just an option. Usually these solenoids are used on farms or big parks. The distance between controller and valves can be up to a few hundred meters. That is why they have AC current as option. AC current is much more lossless over long distances (remember war of currents).
You can find cheap models that should be sufficient for home use starting around 10 Dollar and the usually need current all the time they are open, but only consume 0.3 to 0.5 A.
But you have to be careful, most models are for outside use only. for in home use i would prefer an electric pump from a bucket. If you need full automatic setup, i would use a mechanical level valve like they use in toilet tanks to keep the water level up. i think that's much more on the safe side.
here is a pretty fricking good offer thats i can't buy because shipping to thailand is just too expensive.
Good information, however one possible misconception:
"That is why they have AC current as option. AC current is much more lossless over long distances (remember war of currents)."
AC current is no more 'lossless' at the SAME voltage as DC current. Only because AC voltages can be easily transformed to higher voltages which allows more power (less I2R losses) to flow in a given size conductor. At 24 volts there is no inherit advantage to AC Vs DC as far as wiring losses are concerned.
SSzretter, that model looks good-- I hadn't found any magnetic latching solenoids as large as that, previously. Of course, it's in India and I have no idea how to price or order it in the US.
