DYI Electronic Flood Alarm & Pump Switch

[pedcab]

Hi everyone

Following a recente PBO article (PBO 493 & 497)about a simple single PNP transistor bilge flood alarm, I´ve decided to share with you guys an upgrade to that system that I´ve came up with.

It´s an electronic water sensor coupled with a relay that can be used to command a water pump.

If the water reaches the level at which the probe points are placed an alarm will sound and the system will engage a relay that commands the bilge pump, turning it on utill the water level decreases bellow the probe level.




NOTES:
-The probe points must be kept at about 10mm from eachother;

-The relay contacts must be properly rated to be able to cope with the pump consumption;


Doubts and suggestions are welcome.

Regards

Pedro

[goboatingnow]

Using a DC source injects a leakage current into teh bilge water, really it should be AC

[pedcab]

Yep, in fact it does have a leakeage current. But, being inferior to 0.5mA, I think it is negligible for this application...

[travler37]

Originally Posted by goboatingnow

Using a DC source injects a leakage current into teh bilge water, really it should be AC

Leakage?
Explain this to a non-electrical person please?Does it leak all the time or only when the water reaches the switch?

If this is so and your AC switch ground failed could not you have a shocking experance placing one foot in the bildge water and touching a ground?

Confused as useall
Mark

[goboatingnow]

not all AC is high voltage.

There primary reason for using a low voltage AC supply to the probes is to prevent the probes from suffering electrolytic corosion. ALso any impressed current flowing through the probes into a wet bilge adds to the electrolytic corrosion issues in the boat in general

There are a few integrated circuits on teh market that use an AC probe , rather then the DC proble here.

Dont get me wrong though the circuit is fine. its only a small point.

[waltsn]

If the sense probes were in the water a lot, you are putting 12 volts on them and electrolysis would be an issue. But, the probes of course are dry most of the time.

One other completely unimportant note about using AC beside elecrolysis. With the DC circuit, you are essentially measuring impedance between the nodes and the impedance of water can vary by a factor of 1000 from fresh to salt. If you had very clean fresh water in the bilge from rain (and your bilge was very clean to begin with), would the detector still work? No doubt it works with salt water.

But with AC, the circuit could be set up to measure capacitance. The capacitance of the nodes in salt or fresh water would be close to the same value and the capacitance between the probes in air and water would differ by a factor of 80 - easy to detect.

[pedcab]

Avoiding electronic discussions that are not easily understandable by everyone, here are some clarifications to the questions "on the table":

1- Sensitivity is not an issue with this circuit. In fact, it will work with anything from fresh bottled water to the saltiest solution over wich you folks may have the pleasure of sail;

2- About electrolytic corrosion, that´s not my back yard. All my life I´ve been sailing wooden boats and, as such, cannot guarantee that this circuit is fail proof for use on boats prone to suffer from electrolytic corrosion;

3- Leak currents: In what comes to shock hazard, battery drainage and other issues of the kind, the circuit is perfectly safe. If anyone is interested but doesn´t trust my words, play it extra extra extra safe. Guess what: The alarm can be ran out of a 9V transistor radio battery. No electrocussion can be obtained out of that. Not even with every last one of Murphy´s laws conspiring at the same instat over your vessel.

Regards

Pedro

[Deadeye]

This is probably a REALLY dumb question and I hesitate to ask, but why not just use a float switch to trigger the relay ?

[pedcab]

No question is dumb...

I don´t like float switches mainly because of two things:

a) They need a much higher water level to actuate;
b) Being electromechanical they´re, in my opinion, much less reliable that a sensor with no moving parts.
c) You can build one of these with less than 10€ worth of components


regards

pedro

[sailortjk1]

Its not DIY and Its not very cheap, but I just received this from Jamestown a couple of days ago......... I had not heard of a product like this before.

Boatsense Remote Vessel Monitoring System