"David Flew" wrote:

....

As a suggestion, we need something which is 12V DC powered, minimal current
draw, uses conductivity between well spaced electrodes, AC to the electrodes
to prevent corrosion, time delay on and off, totally impervious to water,
protected from short circuit, reverse polarity, excess load, can be home
built, cheap ...
I can dream about the specs, I could build it from a kit, but I would not
have a clue where to start for a design.


I've built just that. It uses a cheap microprocessor from Microchip,
stainless steel bolts as the sensors. It puts AC on the sensors to
avoid electrolysis and plating. It solves the "splash" problem by
having to detect water continuously for 15 seconds before turning off
the pump. Same with turning off - no water detected for 10 seconds.

It's biggest problem is crud in the bilge water - oil being the worst.
It will eventually coat the screws and insulate them from the water.

I've never tried it in salt water, as I sail on Lake Ontario.

Because of the crud problem, I modified it to measure the current
drawn by the pump motor. When pumping water, it draws more than when
pumping air. The processor turns on the motor every (say) 15 minutes
for a few milliseconds and measures the current. The pump will run
until the current indicates that the water is all gone. It also
detects a motor stall condition, and shuts off the motor (and flashes
a red LED to let you know)

This works like a charm. In fact, I use both systems now - the sensors
and the current.
Larry Bradley VE3CRX
Remove "removeme" from my e-mail address for direct mail
Ottawa, Canada

(use the e-mail address above to send directly to me)


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