If you cover the postage you are welcome to my old model submarine bilge/compressor switch.It is 0.9 x 2.5 inches and will handle very big pump.

Alternatively, I got the above circuit from an old article.

For your application I see no reason why R2 can’t be replaced by 1M and the probes be at Q2 input and the negative supply and Q1 be omitted.

The positive probe will become pitted due to electrolysis on d.c. probes.

I’ll bet problems occur if the bilge water comes into contact with the negative supply (unless the probe sensitivity is increased by reducing R1to 10k or the more positive bilge probe shroulds the lower probe.)

If fitting a float switch is no problem,it could replace R4 while ensuring Q3 is turned “off” by a pull down resistor when the float switch is open.

The simplest solution of all could comprise a “TOPFET” in place of Q3, float switch and one resistor.

Regards

Lee Penny

Hi Mick,

Just P.M.your address and I’ll check it before sending it off with the connections and my own address.

I haven’t posted a packet since the new rates but I doubt it will even come to a book of four 2nds.

Lee

OK – I admit it – I’m thick !

water comes into the hull and operates the float switch or circuit probes and switches on the pump which pumps the water out, when the water is gone the float switch drops back down and stops the pump.

This much I understand, now comes the thicky part of me asking WHY, do you need a float switch or a fancy circuit board ?

if you connect +12v to the pump and run -12v to one of 2 small nails/screws set in a small block and fixed near to the hull floor and a 2nd wire from the other nail/screw to the pump.  surely water coming into the hull, which is a damned good conductor of 12v would, when reaching the nails make a connection and switch the thing on – when the water is gone the connection would be lost and it would stop !

Either there is something seriously wrong with my way of thinking or people just like to make life harder for themselves.

Ken – the stupid

MIck   Regarding your bilge pump, I reckon the best way to go about this problem is to gey a smallD.C motor driven pump that works, and get an electronics chum to build a little sensing circuit with a 731 integrated circuitthat looks at the resistance between two electrodes right down in the bilges, and as soon as water is present, the circuit will enable a driver transistor which switches on a power transistorthat applies power to your little pump motor. there are lots of published application circuits available, so you don’t have to worry about infringing copyright asthere are plenty in the public domain. the one I have in mind is very economical on power, as it only switches on when needed, and off again when the water’s gone. just remember the word application when you are searching for the right one.

Cheers………………..Mike     D

Simply get a fuel pump and motor…connect it to the battery…fit an on/off switch…and use that when necessary

Bob

Good morning Paul

We didn`t get to Blackpool afterall!…………………Had a nice day at New Brighton……….Saw the Illustrious leaving port………………..Had the wrong camera with me……Hence no pictures!

Apologies to Mick for going off topic………………that`s your fault Paul!

I`ve got bilge pumps in most of my big boats…..some simple on/off and some servo operated.

Bye…………..Bob

Hello Paul

That`s the problem!………………….The Great Eastern is a hard act to follow!………………………I`m really struggling for the right subject to appear on the horizon………………something will turn up soon I hope………my workshop looks like a British shipyard at the moment………………….idle hands and total desolation!

Bob

Thanks Duckie

Guess what I`m looking at……..at the moment?…………………Hmmmmmmmmmmmmm?

SS Jeanie Deans as she appeared in WW2!……………………..This could be it!

Camoflage….guns……mine racks……..no rivet counters about……windows covered…now portholes……and I`ve got the plan already!

What a pity, I messed up the formers making Great Eastern

Even more apologies to Mike for going off topic…….but I will be fitting a bilge pump!

Now where`s that plan?

Bob the Builder!

Paul………………I`m quite excited about the project……………..and that`s good enough for me!

It`s also quite a challenge………………because I can`t remember a damned thing how I built the original Jeanie Deans!………all the photos got wiped off in error!

It will look very nice with the camo colour scheme and not forgetting the card and rivets trick!………and for a novelty…..how about some explodong mines?

And as far as I am aware………………….it ain`t been done before!

Going out for the wood this afternoon!

Bob the Builder

Thanks a lot Paul………………..I knew you would sniff something out……………….haven`t seen your picture before.

Got the wood and a large PVA………………It`ll be like old times again, especially now that I`ll rarin` to go!

Bob