Opinions on float switches?

[Richard B]

Originally Posted by Nick Hensel

Its fully electronic and doesnt use probes or float switches but instead tries to pump every 2.5 minutes. If there is water present it continues to pump until the sump is empty then stops........ So far I have left it for about 10 days in a row and the 110Ah battery was fine. (Draws very little current when in check mode)

We've left a boat in the water from Xmas to Easter using one of these pumps and the battery lasted for that length of time - just about (just enough charge left to turn the engine over a few times). I think that they do operate at full current for the test phase, but only for a short time (about 5secs IIRC).

[jwalker]

The bilge pump circuit described above has a flaw. It does work and the pump will certainly switch on as planned but, depending on the relay used, it may not switch off for a while. The reason appears to be because a relay requires more current to pull it in than it requires to hold it in. When water is sensed the pump switches on. When the water level falls from the sening probes they will be damp and this dampness may still be conductive enough to hold the relay on. The reason for using this type of circuit was to limit the current consumption to almost zero when the boat is not in use.

A better circuit is given below but it is active in that it consumes some current at all times, however, in the two I have built, this is only 1.9mA. (0.0019amps)

It is a straight forward comparator but using the CA3140 op-amp which consumes very little current and it is also good for use on a normal battery supply. The wee circuit on the output from the op-amp simply ensures that any raggedness in the supply or across the probes does not cause rapid on/off switching but it doesn't introduce hysteresis. By increasing the value of the capacitor it is possible to cause the pump to switch on for a minimum length of time, say 5 seconds, if this is felt to be an advantage.

They have been tested in anger (Had a fkkn leak!) and they worked a treat.

Calibration was done by soldering a couple of bits of offcut wire where the probes connect to the board and dipping them into a glass of fresh water. The preset is then turned until the LED lights and then turned a touch more to ensure a positive trigger. I thought that this would probably need to be recalibrated for salt water once in the boat but it worked fine.

[jwalker]

Oops... missed out the 1k resistor in series with the LED and a break in the +ve track.

[Erin]

Hi JW

Time for a Maplin order I think. Thanks for the design.

Cheers
Keith

[Erin]

I built jw's latest design and it works a treat. Now all i've got to do is waterproof it all and fit it.

Thanks jw.

[quinquarimarine]

JW

Fair play you have spent more time and energy working on a system that took me many years. Most of the vessels we own or supply are deep water moored and an efficient bilge system in force 9 plus is of significance to the point that we always fit a twin bilge with independant batteries.

Auto systems tend to work on various number of principles

1. A merc switch
2. Mechanical ball switch
3. Earth resistance
4. Back pressure sensor.

One of the important points to any system is the delay in detecting a water level and the intruction to start pumping. This is why we like the computerised method as it avoids false starts in a heavy sea.

After many years we have found the Rule 2000 and 3000 computerised systems the best and they work on back pressure sensor. Of over 50 supplied we only last week had the first one returned. Of caution though the filter in the base must be checked on a regular basis and the major failure with all pumps is human hair---- it falls onto the deck, goes aft into the well and when spinning round the pump makes a very strong rope. So every so often turn the pump upside down and pick the hairs out !!..... dont let your wife do it in case its not the same colour as her hair !!!!


Cheers

John
www.quinquari.co.uk

[jwalker]

Cool.

[jwalker]

A wee update on auto bilge pump sensors.

This one was designed for a particular purpose. It triggers as the bilge water comes into contact with the sensing probes and the pump runs for a period of time which is adjustable up to approximately 10 minutes. To prevent mistriggering by slopping, the pump will not start to run until the sensors have been in contact with the water for a few seconds.

It's purpose is to allow the bilge water to rise to a predetermined level and then pump it out completely rather than having a pump cycling frequently.

In standby, the circuit draws a tad less than 4mA so that shouldn't be a concern.

Depending on one's preference, fuses can be fitted.

[jwalker]

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