I want to use the SW12 position to switch on a 12V valve during certain periods of the day. After a bit of struggling with the code, I finally got it to work! I am using a Do Loop with time as the trigger. Now, my problem is that when the 12V is supplied, other things shut off. Twice when I activated the 12 V by manually putting the wire in the 12V port, the computer (connected through the Serial/USB cord) froze. The next time the 12 V was switched on automatically using the program, it shut off the data logger completely. Of course, this happened at 1:00 in the morning, and we lost all of the data until we came in and restarted the logger in the morning.
The valve I am activating is a Skinner B-Series, 3-way valve. The manual says it consumes 7 watts. I checked the SW-12 limitations, and I think we are OK since the temperature was only ~24 deg C when this issue occurred.
Do you know what the problem could be? Any suggestions would be greatly appreciated.
A few things come to mind... First, based on the variety of problems occurring when you operate the valve, there may be a ground problem. The valve must be referenced to the same 0 volt potential as the logger for this to work.
Second, the 7 W figure could be the holding power, and there may be a much higher inrush current when the valve begins to actuate.
Another concern, once you get the thing working, is that inductive loads such as solenoid coils store energy when turned on, and when turned off that energy needs to go somewhere; unless handled, e.g., using a shorting diode, this will cause arcing across the relay contacts, pitting them and eventually causing failure.
Driving a separate relay or contactor may be a good idea, to isolate the valve power circuit from the logger or computer.
* Last updated by: kirving on 6/24/2011 @ 1:54 PM *