water level relay

For the level switch approach:

Use a power Mosfet, like a STP200NF04, turned on by your level switch. Don't skimp on the Mosfet - it has to handle a large surge current when you first turn the lights on.

:I thought this would be easy, but I'm struggling with the details. : :I have some lights (12VDC 200W) I want to turn on when the water level :in a fountain reaches a certain point (i.e., the fountain is on). : :If I use a level switch and trigger a relay, I have the problem of :figuring out where to put the relay around the fountain (just rocks :and dirt). Do I bury a standard solid state relay in a water-tight :box? I can't really have an above ground box sitting there. : :Is there such a thing as "water resistant" relays? : :thanks!

You have discovered an item many designers tend to forget about.... the "packaging". Even if you could find a water resistant relay you still have to get cables in and out of it so the connection points also need to be waterproof. Your only solution is to use waterproof level sensors (fairly easy) and run the cables back to the controller which is sheltered or doews not allow water ingress. You can use a watertight plastic box which has sealing rings and you can use watertight cable entry glands. Your local Weidmuller distributor can help with IP68 nylon cable glands.

Search the catalog Enclosures/cable entries/IP68 cable glands/Plastic cable glands IP68.

Go to a "Major appliance" Service Parts supplier and look at their Water Level sensors for Dishwashers , Washing machines !. Some Wet/Dry Vacuum cleaners use a Magnetic Float Switch to Shut off !.

Yukio YANO

Why not look into washing machine water level sensor/switch devices? You might turn up something that you can scavenge at a junk yard.

a relay can be packed in a box full of grease... it'd probably survive submerged.

If there's flowing water, is there a pipe to deliver it? You could use a flow-sensing switch, or manometer switch, and not have to put wires among the scenic parts.

I'm a little curious about your parenthetical "i.e., the fountain is on". Do you really want a water level switch or just lights when the fountain is on?

Tom

Water has resistance to it..

depending on the mineral content, I would start with 2.8K ohms as a starting point. Use 2 stainless steel rods about 1 each apart.. One rod being the common/ground and the other the actual level point to sense. Level sense can be used to apply bias on a low current switch that employs a transistor or OP-AMP.

When both the common rod and level sense are submerged they will conduct like a resistor..

this thread has gone a long way, and I'm coming back to the start with a different suggestion.

put the relay next to whatever provides the 12V for the lamps, most likely it will be dry enough there.

this may mean you need to run another conductor or two out to the sensor but it makes life a whole lot simpler.

On the other hand, could you just put a switch for the lights next to the control that starts the fountain ?

Bye. Jasen

If you want the lights on when the pump is running, why don't you just connect the input of the 12 VDC lighting power supply in parallel with the pump motor? Then one switch turns them both on.