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Discussion Starter #1
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
 

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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
 

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Nearly an Old Salt
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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.
 

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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.
 

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Discussion Starter #7 (Edited)
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
 

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

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Discussion Starter #9 (Edited)
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
 

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Bender of Nails
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...I don´t like float switches...
Good enough for me. I asked because, on the boats I was building until recently (starting my own now...woohoo!), we used an in-house bilge alarm and fire system whereby a float switch sent a signal to an LED and Piezo buzzer at the helm station. We stored many of our customers' boats so all the alarms were tested twice a year during maintenance/refit.

If I could add a suggestion, when selecting the horn/buzzer for your alarm make sure you get one that doesn't sound like anything else in the marina. We used the same buzzer available from our wholesaler that West sells. Many times I broke into a run on the dock heading for one of our boats to find it was only some DIYer's homemade alarm system letting everyone know the mercury switch had been triggered by a wake....

Personally, I'm going to wire a flash relay into the spreader lights as well so there's a visual indicator if I'm not on the boat. The anchor light would be a good idea too but I want to keep all the nav lights as a dedicated, independent system.
 

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Discussion Starter #13
Funny of you to mention the flash relay.

Because I keep Fulô at a swinging mooring I also use this system to trigger a led flasher I´ve made with some high intensity white LEDS and a 555 IC.

This way and everytime I park the car at the sailing club I know for sure if its time to paddle all the way down to my boat to clean up any rain water that may have found its way in... :)
 

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My thinking too, is that if an alarm is going off on the boat and I'm not there it'll make it easier for a good samaritan to lend a hand. I know I wouldn't have any compunction about trying to save someone else's boat.

Speaking of 555's, I have one that I'm playing with but electronics aren't my strong suit. I can wire up switch and breaker panels and stuff, but I'm still learning how to read an electronic schematic (old dog, new trick). Is there a reference online that dumbs down what the 555 pins do ? The symbols and abbreviations are still Greek to me and I need a Rosetta Stone of sorts, lol.
 

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Discussion Starter #15
There are tons of great sites on the web with lots of ideas on how to use the 555.

The 555 is one of the most versatile ICs out there. With it you can do anything from a ring tone generator to a timed relay and it is very simple to wire up to do things that can cost great money on stores.

About the pinout description, maybee I´d have a hard time trying to explain it to you (since my english is not very good). For instace, OUT is the output- the signal you can use to trigger a relay, a transistor, etc. VCC is the power input from where the 555 gets its power. RESET is the input by which the IC resets to the initial stage of whatever it is wired to do in a given application...GND is the groud - pin. DISCHARGE is, roughly, the pin where you connect your RC (resistor-capacitor) sub-circuit in order to obtain a desired time constant. Generally speaking, the higher the capacity, or the resistance the longer the time factor, and vice-versa(within reasonable values)... etc, etc, etc...

Anyway, the datasheets of the various 555 manufacturers are usually very compreensive and even provide some application suggestions...


I suggest that you check out these sites that I´ve sorted out of the thousands available on this subject:

555 timer IC - Wikipedia, the free encyclopedia

LM555 Timer Circuits

555 Timer/Oscillator Tutorial

TALKING ELECTRONICS 555 Page1

Hope I´ve been of any help

Regards

Pedro
 

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Has anyone had actual experience with the Boatsense monitor? I love the idea of it: if water is rising in your bilge, or your battery is low, or any of up to 3 other things sets it off, it texts up to 3 phone numbers & says what's wrong. But how hard to install? How reliable? How's customer tech support? And questions like that...
 
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