Hi, I'm building an irrigation timer, I'm wondering about the type of solenoid valve. There are two main types, direct acting and pilot valve type. The pilot valve type uses a small valve to activate a diaphragm which opens the main flow using the water pressure. There is a good explanation of this on Wikipedia under solenoid valve.
I bought a pilot type valve from a local supplier, and after carelessly damaging it bought an industrial quality direct acting valve from Aliexpress, for a slightly lower price. The pilot type has a diaphragm with microscopic holes in it, looks prone to blocking. I'm using 12 volt DC for the valves, the pilot type draws 0.5 amp, the direct acting 3 amp. I'll need 5 solenoid valves.
Does anyone have experience using direct acting valves with irrigation, is there any downside apart from the higher current?
I plan to use darlington TIP122 transistors to turn the valves on and off, these transistors have a very high gain which will enable the arduino output to switch 3 amp. The TIP122 is rated at 5 amp. I understand I will need a "snubber" diode on the solenoid to dissipate the back voltage from the solenoid when it turns off. This diode is wired across the solenoid wires so it doesn't conduct when the solenoid is powered, but momentarily when turned off and the solenoid generates a reverse voltage which might damage the transistor. A fast 1 amp diode is been suggested for the snubber on one web site. "Fast" means there is a very short delay between the diode being reverse biased and conducting in the forward direction when the voltage reverses.
The 1 amp snubber diode was suggested for general use. My direct valve draws 3 amp and so there will initially be 3 amp going through the diode, but only for a short time. Is this ok? I haven't been able to locate 3 amp fast diodes.
There is another issue that there will be a 2 v drop in the TIP122. This is powered by a 12 v battery on a trickle charger, normally 13v. I'll just have to try it and see if the valve will work on 11v
Any solenoid valve can get plugged if the water has trash in it! May get lugged open or get plugged closed or somewhere inbetween. Best to screen out the problems!
Use a zone indexer and just one valve. Every time the water flow stops, the indexer kicks to the next ouput automatically. So one valve can index to, say 6 zones, and water one at a time. This reduces your solenoid count to one and eliminates the need for a massive power supply.
The water comes from a tank and pump. I have a stainless filter on the downside of the pump. There are 100 wires to the inch, so about 0.005" gap between wires taking into account the thickness of the wires. This stops visible particles but I get brown goop going through, algae I guess. I've excluded light as much as I can, and the tank is dark green plastic which I think would exclude light. Looking inside the tank it looks squeaky clean, but I still get brown goop. The goop is probably there in the tank too but not visible till it accumulates on the filter, as I think it would on a pilot valve. The sprinklers cope with this fine.
The indexer is an interesting idea but I think it wouldn't work for me. Most plants don't need watering in winter but there is one area under the eaves which needs watering all year round. My tree orchids need watering once or twice a day but most plants only need watering once every 2 or 3 days.
Indexer is ideal. You can be adaptable because its computer controlled. To skip a feed, just bump the indexer twice. In the winter when only one zone needs water just don't index at all. You can dynamically control the time that any zone gets water. You're still thinking mechanically! LOL
I plan to use a mega pro (chinese). I like this board because it's compact and has plated holes I can solder pin headers into, just for the pins I am going to use. I find the connections are more reliable with male pins than the sockets on genuine boards.
Here is a photo of my last project, a temperature and pressure logger. I made the vero board first then made the case once I'd settled on the layout.
Thanks. I guess the 10k is just a pull down. I still have a lot to learn about electronics. The optocoupler, a good idea to isolate solenoid power from arduino? In my case they are both running off the same battery.
