I want to try building a bilge pump control board
the circuit will activate the pump when the high water level is reached
and deactivate when the low water level is reached
this will be a salt water application so i would like as few metal parts in th water as possible
and if possible avoid voltage through the water
I was thinking two cap/scr latching switches
and 2 floats one for on and one for off this seems a little complicated if anyone has an idea to simplify this or make it work please let me know
thanks
William

 

If it's for pumping out water whenver there's water present in the bottom of (a boat i presume) why not use a float switch like those used for most submersible pumps? Whenever there's water the switch will float, turning the pump on.

If that were what you were meaning, would something like this be suitable?
http://www.google.co.uk/url?sa=t&ct...hCaLps1VI1qpc-K4g&sig2=JPvAHJ2Y32HCfvmJqykCqQ

If you specifically wanted the pump to turn on once a high level was reached then off once it got back below that to a low limit i guess you could use switches mounted horizontally like this one. Kind of a Hysterisis, though I can't think why you'd want to do that.
http://cgi.ebay.co.uk/rs-componets-...004538911QQcmdZViewItem?hash=item380004538911

 

my main intention is to keep most of the electrical componets above the water level
the reason for a a double switch setup is the water must run uphill for a fair distance an as such a normal float switch would cut out before too soon and also the to keep the pump from running dry

 

but...

if you used a normal submersible pump float switch, it would go off when the switch tilts upsidedown because when there is no water the switch will hang upsidedown by the wire attached to the top of the pump, hence turning the pump off (so it wouldn't run dry). If you shortened the cable of the float switch, or put the submersible pump on a stand (several bricks for instance) the pump would turn on when the switch floated upright and turn off when it hung down by the pump's side. Due to it being raised on bricks there'd still be water in the tank/ditch/pond/boat.

Does this solve your problem or am I looking at it in completely the wrong way?

 

the other limitation is i only have 4inches of vertical space and the pump needs to cut out at 1/2 inch of water to i might be able to put a one way valve in the hose to prevent back flow ....
the other way would be a timer to keep the pump active to dry out the bilge using a 555

 

ive tried normal float switches and they constantly switch on and off draining my battery bank

 

That could work. If you work out the flow rate of your pump, you could set the pump up with a relay that turns the pump on when the second switch I posted floats which'll trigger a 555 monostable for a time calculated time to empty your tank to 1/2 an inch of water.

 

Not meaning to inject sarcasm here, but have you considered fixing the leak(s)?

A big problem with battery-operated bilge pumps is that they tend to mask the larger problem; leaks that not only persist, but inevitably get worse over time. Without remedial attention, you eventually will wind up with a boat resting on the bottom with a dead battery. Put in a bigger bilge pump? More pumps, more batteries? It just masks the problem until all the batteries are dead and the boat is on the bottom. Even if you're plugged into shore power, that is not 100% reliable. People have been known to "borrow" extension cords and not return them. Ask me how I know this.

What I feel that would be most useful for you is to install a chronometer in parallel with the bilge pump switch, so that it only runs when the bilge pump is running. That way you will have some way to measure time vs CFM capacity of your pump just how bad your leaks are getting, and make a judgement call as to when you need to drydock it for a time to fix the leaks.

Meanwhile, even deep-cycle marine batteries begin to sulphate when the battery voltage drops below 12.4. Eventually, they'll refuse to take a charge.

If your pump is cycling on and off too frequently, I suggest it is not the bilge pump switch that is at fault; it is a harbinger of your boat's doom.

[eta]been sailing on and off since the late 1960's. Spent quite a few summers at the SYC in Ontario. Was nearly a member of the Tonkin Gulf Yacht Club, but just spent time steaming up & down the coast on CV-59.

 

there are no leaks ... per say the water build up is caused mostly by condensation
the bilge water has no salt content in it ... rain could also be culprit
my goal here was to design a more efficient bilge pump system as a future consideration
as i have previously said the commercially available bilge switching systems on the market seem to fall short in terms of reliability and durability ... i intend to remedy this with my own design
all of your input has been of great assistance
I will put the final project up in the forums hopefully to help other boat owners deal with this issue
William

 

I forgot how cold the water gets that far north. Yes, condensation would be a big problem. If your hull has no insulation, you might consider adding some - although I know how tough it might be to attempt such a feat; and cabin space is always at a premium.

Ideally, your solution would have no moving parts - as moving parts eventually wear out. However, that implies electrical contacts underwater. This will take a bit of thought.

 

I'm thinking a reed switch (or a pair of them) activated by a magnetic ball that is free to roll inside of a sealed PVC tube that is hinged (or simply tied down) near one end. It would exhibit hysteresis, and would draw no standby current. The closing of the reed switch could turn on a power MOSFET, such as an IRFZ14 or IRFZ24, etc - which would provide a ground to the bilge pump.

A pair of such devices on different levels in the bilge would give you a primary and backup system.

Not a final design, of course - just a concept for the moment.

 

Hi,

There are numerous ways to measure the level, but personally, I would try a good composition of stainless steel probes and use AC for measuring to avoid electrolysis - it is both cheap and simple, and if build well, mechanically speaking, should last long.


But if current through water is an absolute no-no (for other reasons than electrolysis), an acrylic or glass rod, with one end pointed to a "90° angle" can be used with an IR emitter and receiver - when above water it will feed most of the IR back up the rod, but when the "angled" point is submersed, the refractive index changes and the IR is "lost" into the water. The IR should be pulsed with a low duty cycle to keep the power drain down of course.

Two length of optical fibers can be used in a similar manner with IR.

Capacitive sensing can be done electrically isolated from the water as well.

None of these methods needs to take up much space and there are no moving parts to service.

 

Sorry to suggest a non-electronic solution, but i'm using an pressure switch with great success.

I'm using a top of a small soda bottle as a funnel, and attached a small hose (1/4" id) to the cork, and mounted it in the bottom of the bilge with 3 small angle-brackets; with the bottom edge of the bottle-neck about 1/2" above the bottom of the keel.

The hose is attached to a pressure switch, found in old washing machines, which i've mounted above the deck. These can be adjusted easily, both on-pressure and off-pressure. Mine is adjusted so it starts the pump when water level is 3", and stops at 1"...

I've used this system in my wooden boat all winter, and it haven't failed me once.

No mechanical parts, and no electric parts in the water.