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Water leak alarm

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saturation:
Yes, thanks for the clarifications.  Yes, its a wonderfully simple design, the only current flow at rest would be reverse junction current flowing in the transistor, which is in the nA.



--- Quote from: 6502nop on August 06, 2012, 08:02:25 am ---Actually, the problem with my alarm wasn't corrosion due to excess current draw, but corrosion due to my probes being copper and suspended over a constantly wet sump pit. The petina that developed was so bad, it failed to alert when needed. I plucked it up off the edge, put my wet finger across the two screws on the top (nickel plated, I think), and off it went. I then flipped it over, and there was my problem. The wires, solder, connections, and components were all good - just the copper went bad. Hence, my recommendation for galvanized probes.

Remember, I also built this to use as a continuity tester, which I threw into a small cardboard box. That was... gee!... 14 years ago, and it's still working. So, input impedance had nothing to do with it. One had copper terminals, the other just regular alligator clips. It was enviornment and materials, not current draw when activated (practically NO current draw when idle - no on/off switch is needed!).

nop

--- End quote ---

SeanB:
Copper probes not the best choice, better is to use 316l stainless steel, so long as the water is not salty. If it is salty then marine bronze would be best, or carbon rods.

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