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Old 31-12-2011, 06:24   #1
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making manual bilge pump automatic

I got annoyed when I find how much auto bilge pumps cost. They charge something like $20 extra just to make them automatic, and I didn't even like how they work, they cycle too much and the one I had quit working after a few months. The pump is fine after 2 years.

I took a float switch I got off the internet for $3. You can get 2 for $5 on ebay if you search for float switch. They are only good for half an amp so can't drive a pump directly, not that you would want to anyway.

So I screwed the float switch inside the end of a pvc pipe with a cap on the end with a small hole 1/16 in hole in it to let water in and out, and the larger hole at the top for air. The idea here is to avoid the sloshing, but it could potentially become clogged, so maybe multiple holes is preferable.

Then I run the float switch wires to trigger a 555 timer chip, and set to to 20 seconds time constant with 10uF cap and 2M ohm resistor. This way the pump always runs 20 seconds when it is triggered from the float, so I can position the float a bit higher in the bilge. I put some leds to indicate pumping, and float sense so I get some feedback, and then have the 555 drive a mosfet which is wired to the pump. I also have a switch so I have manual on and off. The most expensive part here is the switch, so everything cost under $3.

I think this works pretty well, but I have yet to do any extensive testing. Problem is, I fixed all my below waterline leaks, and I don't take too much water from rain either!

What do you think? Any ideas for simpler or more reliable ways?

Any ideas for just using two wires going into the bilge to detect conductivity and trigger the pump that way? Would you need an opamp for this?
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Old 31-12-2011, 06:30   #2
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Re: making manual bilge pump automatic

Wow, I think you went a long way with this! I see two problems:

1. the 1/16" hole will quickly plug up with paper, debris etc. after which the system fails

2. weather proofing the electronics. You will need to test this and then cast it in epoxy to make it last.

My tinkering was limited to the pump on my grey water tank. I mounted a regular Rule float switch under in the tank and connected it to an old Raritan timer-solenoid switch. I then adjusted the timer on the solenoid until the pump ran just long enough to get the last bit out of the tank after the float switch switched off already.

cheers,
Nick.
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Old 31-12-2011, 06:46   #3
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Re: making manual bilge pump automatic

The best switch I've found is the type that operates on air pressure - water rising in a tube of trapped air against a rubber diaphram which actuates a mercury switch.
A unit like this is mounted above the bilge water and never gets wet. I had these switches on my fishing boat for years. Never had a problem.
Submersable switches just don't last as long.
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Old 31-12-2011, 08:38   #4
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Re: making manual bilge pump automatic

IMHO, you are re-inventing the wheel, albiet a nifty "cast Mag " wheel
I am all for KISS. My bilges are deep wine-glass shape. I mounted one of those pivot type switches up high at salon floor level. Gillnet donut float attached to lightweight f/glass tube guided vertically by screweyes in bulkhead. Float lifts tube, tube lifts switch. Voila!! I can test switch without digging in bilges.
Belt driven pumps up high. No way am I going to submerge the thing (pump) which is supposed to keep me alive, in the very medium which is trying to kill me, and in a location that when the thing stops working, I can't get at it to fix--because my head is under water drowning--if you get my drift.
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Old 01-01-2012, 09:24   #5
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Re: making manual bilge pump automatic

Happy New Year!
It just came to me - what you need is a Reed switch and your problem solved!
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