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Old 01-20-2010
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Bilge sensor without moving parts

I was studying electronics exam and i was thinking of using a darlington transistor as a bilge watersensor.

Is this good or did i miss something?



The base and collector are connected to lengths of wire, hung in the bilge (deepest point).
Collector is conected to +
Emittor to + side of pump
Negative side of pump to negative-pole of battery.

The darlington can easily be encapsuled in silicone to protect is from water.
these components are really cheap (less than 5$ for the setup i think).
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Old 01-20-2010
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i have the ultima switch, it is the longest lasting switch i have hard so far.

about 30 bucks
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Old 01-20-2010
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The wires will be the weak point as they will corrode and the point at which they operate will vary but you can explain on the exam that the wires have stainless steel caps on them. The ultima switch uses capacitance to detect water level. No exposed wires at all.
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Old 01-21-2010
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Hello!

You need not a darlington pair (why did you thought of using one? A single stage is enough) and you should go for PNP to avoid the problems that would arise from the remote possibility of another part of the negative circuit touching the bilge water...

Check this thread I've started on the subject:

ww.sailnet.com/forums/electrical-systems/49930-dyi-electronic-flood-alarm-pump-switch.html



Regards!
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Last edited by pedcab; 01-21-2010 at 02:43 PM.
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Old 01-21-2010
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How about using no moving parts and no electronics in the bilge? I use the pneumatic swtich that consists of a pressure diaphragm switch remote from the bilge. A plastic bell recieves the rising water and tygon tubing leading from the top of this bell transfers this increased air pressure to activate the high and dry switch. No cause to put electronics in the bilge water. 'take care and joy, Aythya crew
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Old 01-21-2010
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Quote:
Originally Posted by CaptainForce View Post
How about using no moving parts and no electronics in the bilge? I use the pneumatic swtich that consists of a pressure diaphragm switch remote from the bilge. A plastic bell recieves the rising water and tygon tubing leading from the top of this bell transfers this increased air pressure to activate the high and dry switch. No cause to put electronics in the bilge water. 'take care and joy, Aythya crew
Seems efficient and reliable, but pretty useless for someone who's intention is designing an electronics project


Also, please keep in mind that with this design no other electronics, other that the nude points of two lengths of wire, need to be in the bilge.

The circuit itself can and should be safely "upstairs"

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Last edited by pedcab; 01-21-2010 at 02:51 PM.
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Old 01-21-2010
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I'm not a marine engineer, but....

To do this, you are depending on the conductivity of the bilge water to provide sufficient base current to drive the darlington. That would probably work in salt water, but what about in fresh water? Other points to consider are that the submerged electrodes could become fouled, and less conductive. Probably the most important thing is that you would have a 'hot' bilge, which would likely blow the fuse on the pump circuit. Using the PNP darlington as suggested would negate that.

In terms of the circuit itself, you would probably want to build some hysteresis into the circuit to limit cycling.

My least technical insight is that it is difficult for a hobbyist to build hardware that is rugged enough for a critical marine application. Do you want to trust your boat and life to it? Have a backup...

Fair winds.

Last edited by ottos; 01-22-2010 at 08:43 AM.
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Old 01-21-2010
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Some years ago Practical Sailor reviewed all the magic-no-moving-parts bilge pump switches and found there was one common problem with them all: They still fail.

Either there's slime or oil or crud in the bilge, which tricks capacitance and conductance gizmos, or there's some other subtle problem. You could probably make it work in any number of ways, but they found a cheap float mechanism to be about as robust and reliable as anything else in the long run. A toilet float assembly, magnet and reed switch, all nicely sealed and potted, and you'd have something quite good enough. Emphasis on "nicely sealed and potted".

If you do go with electronics? Remember the engine starter will routinely throw 200VDC spikes into anything that is always connected--like the bilge pump switch--and you'll need to spike protect it as well as keep it dry.

Last edited by hellosailor; 01-21-2010 at 09:28 PM.
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Old 01-21-2010
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how a bout a broomstick with a pingpong ball taped to the bottom end. drop the bottom of the broom stick into the bilge and wedge the top under the bilge pump switch on your electric panel. When the bilge level rises, the broomstick nudges the switch on. No moving parts, no wire to corrode.
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Old 01-21-2010
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Using bare wires in the bilge could be a problem. In my salt water fish tank I used a titanium bicycle spoke as a probe in the water all the time. Never corroded or discolored.
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