Electronics Forum / Basics / August 2008

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.

  +12 ---+--[Lights]---+
         |             |
         |<|        ||- D
           |        |<-.  STP200NF04
           +---+----|  |
               |   g   |s
             [1M]      |
               |       |
 Gnd-----------+-------+

But your post begs the question why use a level switch,
if the lights are supposed to turn on whenever the
fountain is running?  Can't you have whatever turns the
fountain on also turn the lights on?

Ed

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.
http://www.weidmuller.com/

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.

On Aug 27, 6:12 pm, d...@swensenscientific.com wrote:

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..

http://webpages.charter.net/jamie_5"

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.