Well, as luck would have it, my own hose water timer died just as we're having this discussion. It didn't 'die' exactly, but it began leaking out of the housing. The unit is an Orbit Single Dial Water timer (http://www.amazon.com/Orbit-62061N-91213-Single-Dial-Water-Timer/dp/B004INGS8S)
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In any case, I replaced the Orbit and, having had this discussion, decided to take it apart (I probably would have done that anyway, but was even more 'inspired' now).
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After learning #4 above, I've concluded that the plunger must get magnetized from the heavy pulse and, consequently 'sticks' in the open position until it's demagnetized (or reverse polarized) by the close pulse. Regardless, my conclusion is that a similar type of drive as I use on my own sprinkler control could be used for this type of solenoid as well. The only caveat is that the voltage and current is much higher.
I measured pulses that peak at about 22 volts and over 3 1/2 Amps! That's a lot of energy!
Attached below are my measurements. Yellow trace is current at 1A/V and the blue trace is voltage (10V/div).
Wow. Just wow! I can't believe my luck and how timely this is!
This forum is great for sharing ideas and knowledge.
For a long time (a couple of years, on and off, but definitely for *too* long) I have been working on a DC latching solenoid-based water valve controller. The valves have always being made by Orbit. Initially, they were of this type:
http://www.amazon.com/Orbit-62035-Extra-Watering-System/dp/B0016HQOYC/About 8 years ago I bought two Orbit kits, each with a couple of these valves and a timer. These valves are now discontinued, and while the timers are pretty decent, their limitations (mainly that I hated when it rained in the middle of the night and there was no way for the timer to know there was no need to turn on the valves right before sunrise) is what planted in me an obsession to built a better controller for the type of water valves that can be operated by batteries, i.e. DC latching solenoid-based water valves.
So, about two years ago I started to research, standing on the shoulders of giants, how to drive the above valves:
http://blog.chapus.net/orbit-62035-redux/Using data from this research I started the design of my own controller. Along the way I found out that the above valves were discontinued and replaced by the valves that (I think) your valve controller drives, Tom. Am I correct to infer that your controller drives valves like these?
http://www.amazon.com/dp/B002HJOUYY?psc=1Because my original valves were discontinued, I designed my project (borrowing ideas from some other people's work) so it could handle both types of valves (either/or) -- one side of the PCB would handle the old valves, and the other side would handle the new valves. My thought was that eventually my old valves were going to die and I was going to have to replace them with the new generation valves, so I decided it was better to design for the future.
Fast forward to today and you will find me doing "field tests" of this project. The problem I ran into is that things "kind of" work, meaning the valves (the new generation, which starting this year I am using exclusively) would open/close "most of the time". This is obviously catastrophic in this scenario -- imagine a valve that fails to close when you are not around to notice.
Why do I think I am so lucky and the timing of Tom's post is perfect? Well, I can't find any major flaws in my design, both hardware and software (perhaps some of you will, and I'd love to hear about it). And yet, the darn valves won't activate sometimes, so I have been scratching my head for a while. My next move was going to purchase a timer that can control the new generation valves to scope the output and make my own controller behave the same way. In fact, I was planning to go to Lowe's this weekend to get me one of these controllers. But, that won't be necessary now because Tom has just provided the measurements that I need!
Is that time base 4 milliseconds, for a pulse length of about 16 milliseconds,Tom? If so, I think my problem is too low initial voltage and two long of a pulse (I was using around 18 VDC, and afraid of going higher out of fear of damaging the valve, and 20 milliseconds), which are easy to change by modifying my device's configuration.
Once I am sure everything is working well 100% I will publish the software, the Eagle files, and documentation. As a preview, I am attaching a PNG of my design (it does not use a Moteino but the next generation will), a picture of a partially assembled board and a board before going into the reflow oven, and a picture of the board I have in the yard for my field tests (the twisted pair wires are for measurements with a scope on the other side of the brick foundation).
Thanks again Tom!
Cheers,
Eloy Paris.-