Miles Mauldin wrote:
Personally, I believe any leakage of RF or EMI around a filter would not be significant to distroy any device that is properly grounded. I do believe any wires connecting to a device can "pick-up" random RF just like an antenna and depending on the source location and power level CAN be distructive to electronics connected to them. In the case of my irrigation system controller I firmly believe the zone valve control wires acted like an antenna and carried RF directly into the controller. There two cables, five conductors each feeding into the control unit. I do not believe the power source for the controller had anything to do with the failure. I'm thinking if I place a ferrite core on each cable as close the terminal connections that it may protect the device. Thoughts?
The problem is that you don't know if the damage is a "common mode" or "differential mode" pickup. something around the whole thing would suppress common mode, but not differential mode.
In any case, a EMI suppression type ferrite is likely not going to suppress the signals you are concerned about.. they're more aimed at VHF and up sorts of emissions.
What you probably want is something more like a bunch of low pass filters, one on each lead, or a transient suppressor from each lead to ground. Take a look at transient suppressors for antenna rotators, weather stations, xBaseT ethernet, or telephone lines. (although phone lines have 48V on them all the time plus a 90V ring signal, while your sprinkler device probably dies with a 50V transient on the valve lines)
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