best bilge pump switch

[scottyt]

with the systems like below ( both ) there is no power draw unless the pump is on. there is a back up with the drawing below, if the lower float does not turn on the upper float will run the pump but only when it is closed. so it wont totally clear the bilge but it wont keep filling past the upper. but when the lower is closed and the upper is closed the pump will continue to run till the lower opens. i like the thought that if the bilge fills past the upper float it will run even with the lower still open, ie broke or jammed




now the one below would need a double pole relay. but it wont allow the pump to run unless both switches are closed. it loses some safety back up if you ask me for that reason.

[scottyt]

now paul if you want to look this up on the internet, to see other options on these circuits google "3 wire start stop". another nice option with this that gives other back ups it if you added a second upper float in parallel with the existing upper either same height or higher it would give you a real back up. now this only works with the first system. but both uppers would have to fail before it would not work.

now you could do a hybrid of the 2 with a third upper float switch say right at sole level that can turn on the system when the water reaches the sole height. but it would only run when it was closed and it would ignore both other switches. in this case i would rather have a normal float activating a really big pump, that way if the others get over wellemed or fail it is there to keep the boat from sinking

[jenningsp]

Hi scottyt,

That makes sense - and is simple. The only issue I can see that you'd have to watch is that in your first diagram, which I agree the redundancy makes safer, the current runs directly through the switch which could be an issue (many switches don't have current ratings that high). This could be solved of course by putting another relay in which is purely from that switch.

Using relays is an interesting alternative. I'm not sure which I prefer: relays or logic gates. They both have benefits and disadvantages. Logic gates are probably cheaper, but not significantly so.

Thanks for the enlightenment: I think it gives everyone a couple of great options.

As I pointed out in my original post, I think that the key here is the hysteresis that is in these systems. That stops the problems associated with just a single switch.

Cheers,
Paul.

[scottyt]

paul the switches are standard float switches, so they can handle the full load from the bilge pump.

as for price, i think relays are running about 10 bucks now, and 2 standard float switches run what about 20 bucks each