- This topic is empty.
December 26, 2013 at 12:33 am #22719
I couldn’t find anything when I searched this forum, so if this has been covered already, my apologies!
I am planning a vegetable garden that is about 40 feet away from the nearest point of the house (my garage). I am not sure what kind of valves I can use to water each of the 9 beds I will have. I don;t have any sprinklers, and from what I’ve read those valves are typically 24V AC. I was hoping to use some cheaper 12V DC valves, but before I order anything I wanted to be sure those could be used.
Basically I plan on having a 10 gallon tank sitting 3 feet off the ground with a water pump and a water level sensor. This will allow me to ensure that there is always sufficient water in the tank. I then plan on having gravity feeds to individual beds, with a valve for each feed. That will allow me to control which bed gets watered.
My confusion is around the specifications of the valves and pump to order… Any guidance is greatly appreciated.
LanewsaDecember 26, 2013 at 6:27 am #25869
There have been some discussions on the forum about interfacing with DC valves. For example, take a look at this thread:
Pretty much the only change is to replace triacs (i.e. AC transistors) with transistors like 2N3904 or mosfets like BS170. The selection has to depend on the current rating of your DC valves. The issue with triac is that it needs a zero-crossing in the voltage to turn off, so it’s only suitable for AC power. Since DC power does not have zero-crossing, once turned on, the triac will not turn off until you cut off power. The thread above also mentioned flyback diodes. From OpenSprinkler 2.1, there are either MOVs or TVS on the board, which can act for flyback voltage protection, so you don’t need to add separate flyback diodes any more.December 26, 2013 at 12:21 pm #25870
Hi Ray, thanks! So with OSPi 2.1 onwards, I will need to replace only the triacs? Since I am planning on adding an expansion board as well, I’ll also need to replace the triacs on that, correct? BTW, is OSPi 2.1 available now?December 26, 2013 at 2:59 pm #25871
Sorry I got confused and didn’t notice this is referring to OSPi. The current OSPi version (v1.3) does not have MOV or TVS installed on the board, so in addition to replacing triacs with transistors, you also need to add flyback diodes.December 26, 2013 at 4:59 pm #25872
Thanks! A bit more work, but the 12VDC valves a lot cheaper!December 30, 2013 at 4:54 pm #25873
Q: What size valves would you recommend — 1″ or 3/4″? Thanks!December 30, 2013 at 5:24 pm #25874
The physical size does not matter. What matters is the electric spec. For example, if the valve draws 200mA of current, make sure the transistor or mosfet you are using can supply that amount of current. Since this is DC valve, you can measure the resistance on the two wires and divide 12V by the resistance. That will give you an idea of the operating current.December 30, 2013 at 6:02 pm #25875
- You must be logged in to reply to this topic.