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Water low, switch help, please

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Posted by I can't do that Dave on July 9, 2005, 10:54 pm


I am just putting in a pressure system to the garage so Momma can
finally go buy a washing machine. <g> It will run from 110v, either our
inverter, wind/sun-willing or the generator.

The pump manual is emphatic about not running dry.

The only low level switches I have found are in the $60 range. Hell
this thing is unlikely to ever get to turn off as the water supply is
almost 100% guaranteed, so $60 at the bottom of the tank and never
used seems steep for me.

Anyone got a neat idea for a low cost low level switch? The water is in
a 4' diameter round tank laying on it's side and I cannot put holes in
it to weld in a fitting so the sensor will have to come through the 4"
dia. access hole at the top. I have a small machine shop so making
stuff will not be a problem.

Thanks in advance


Posted by Harry Chickpea on July 9, 2005, 11:47 pm

Why go thru the top at all?  Use a microswitch, a springor
counterwieght, and enough tubing at the top to allow for a small
amount of weight deflection, and weigh the tank.

Posted by wmbjk on July 9, 2005, 11:55 pm

On 9 Jul 2005 15:54:11 -0700, "I can't do that Dave"

A standard float switch (about $5), switching a $0 contactor
supplying power to the washer, should do nicely. You'd want a float
with contacts that open when the float drops, as opposed to the more
common version which has contacts that close when the float drops.
Although the operation of either can be reversed by doubling the float
back onto its lead and tying it in that position.

Easiest installation method is probably like this - bore a hole
through the access cap. Attach a J box using a 1/2" pvc threaded
adaptor through the hole. Attach a piece of 1/2" pvc conduit to the
adaptor so that the conduit ends perhaps 12" from the bottom of the
tank. Thread the float lead up through the conduit, and into the J
box. Inside the box, tie a knot in the lead to adjust the float height
so that its contacts will open when the tank is nearly empty. Make
connections in the box to go the contactor, which can be mounted
anywhere convenient. Leave enough slack in all the wiring so that you
can lift off the cap including the float and conduit, so that you can
manipulate the float by hand to test operation. Add a switch if you
want to eliminate idle power draw when the washer isn't running. But
you won't need that feature if the whole thing is generator powered.

If you'll be having a separate pressure switch controlling the
pressure pump, you might want to use one with a "low water cutoff"
lever, to protect the pump from running dry. These cost about $ more
than the standard ones. They work by opening the contacts if the
pressure drops too far when the pump can't keep up with demand (such
as when the storage tank runs dry). The contacts can only be re closed
by holding up the lever until pressure climbs past the trip point. You
could power the pressure pump through the same system as the washer
instead, but then you'd have power being wasted by the contactor full


Posted by Bill Kaszeta / Photovoltaic Re on July 10, 2005, 12:11 am

Try one of those level sensor switches used in washing machines.
You may need a relay because they open the circuit to the fill solenoid
when the washing machine is filled to the desired level.  Sensitive
to a few inches of water.  Available as replacement parts or used.

Bill Kaszeta
Photovoltaic Resources Int'l
Tempe  Arizona  USA

Posted by William P. N. Smith on July 10, 2005, 12:24 am

http://omega.com/  has more level switches than you can shake a stick
at, in lots of price ranges and formats.  Also, your local boat store
might have a bilge pump float switch that might work.

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