Sensing switch closure with & without power applied?

| Yes, but what I was trying to say is that all those suggestions saying | "replace the switch with such and such" might not be viable.

Run an AF signal down the same cable and detect it - 20 KHz should be fine. I've even seen 3 VDC used for similar purposes but you need honking big chokes to isolate it.

Do you have access to the switch leads, just raw, at the top of the well?

Then get a little battery-back-up supply - Maybe a hobby-sized lead-acid on a float charge - and use the switch to control the coil of a 12V relay. Use the relay contacts to control whatever you want, (like control the pump, or not[0]) and it exactly follows the state of the switch, mains power or no.

Good Luck! Rich

Kibo informs me that DaveC stated that:

The least invasive (ie; safest) method would be to put a pickup coil near the mains side of the cable, to detect 50/60Hz leakage when power is available.

Use a double pole double throw switch, one site for the load and one side for the position.

???????? The O/P did post "It's a float-operated microswitch in a well." This may not exactly lend itself to that.

Except that it doesn't solve the problem if he has to go down into the well and replace the switch. :)

--- sam | Sci.Electronics.Repair FAQ Mirror:

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Ok, use a SPDT switch and assume that if one set of contacts is open, the other must be closed.

It was also not specified that the switch was double-throw. The only information given was one contact closure.

But then again, I've asked the OP about the switch itself, and what's actually accessible, and haven't seen a response yet - maybe he's solved it and hasn't bothered to come back and say so.

Thanks, Rich

There are circuit breakers, of larger size, maybe 120 A and over, that can sense their/open close condition, with auxilliary contacts.You may find a residence-rated circuit breaker with this capability (also 40A, 63A-don't know which size is standard in the USA).In HV gear this is a must;nothing can be operated with 150 or 400 kV, except with the use of potential transformers.Many LV breakers are supplied with a set of auxilliary contacts.What is the circuit you want to control?

-- Tzortzakakis Dimitri?s major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr ? "DaveC" ?????? ??? ?????? news: snipped-for-privacy@news.individual.net...

On Tue, 11 Jan 2005 22:19:53 -0800, Rich Grise wrote (in article ):

I've pretty much settled on the solution suggested by Fred Bloggs, earlier in this thread which uses 2 relays:

One relay (d.p.) is set or released by mains voltage. When enabled, the float switch (using mains voltage) controls a second relay (s.p.) which closes the alarm contacts if/when the level rises in the well. When power has failed, the primary relay, now de-energized, connects the float switch directly to the alarm contacts (using battery voltage).

It seems the simplest solution.

He'll hire you to climb down into the well! :)

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Thanks for the update. I'm glad to hear you've got it solved. :-)

Cheers! Rich

Usually these switches have two (at least) set of contacts.You can use one for control, it is usually (here) one NO and one NC.A 4 core cable to the switch will do.

-- Tzortzakakis Dimitri?s major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr ? "DaveC" ?????? ??? ?????? news: snipped-for-privacy@news.individual.net...

Or 380 V ac in Europe.

-- Tzortzakakis Dimitri?s major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr ? "Fred Bloggs" ???a?e st? µ???µa news: snipped-for-privacy@nospam.com...

In college, we learnt about a float switch, japanese origination, with three immersible contacts.One at the bottom;one in the middle of the well/tank and one near the highest level.The way it works is obvious.

-- Tzortzakakis Dimitriïs major > On Fri, 7 Jan 2005 17:09:10 -0800, Palindra~»me wrote

LOL, well, you won't need the sign then - unless you work for the Mafia.

As well as my original, rather more serious suggestion, echoed by other posters, of using change-over contacts and the very sensible suggestion of using the switch to control a mains relay - which can have auxiliary contacts, if need be, you might want to consider:

Stick another float-switch down the well and wire that to you alarm circuitry.

Not only does that give electrical isolation, it also means that you have a fail-safe - should the existing switch fail or get jammed. This can be invaluable.

Presumably you are worried about too high well levels (it happens here in the UK with some wells in cellars of old houses - unless you start pumping, you end up with a full cellar, which plays havoc with the port). In which case a fail safe alarm that says the well isn't being pumped down could be invaluable. You can set the alarm switch point a little higher than the pump switch float, to save heart attacks..

Or are worried about "pumping" an empty well (which also happens in the UK) and thus wrecking the pump? Presumably not, as not much pumping is going to happen anyway, with no power.

On both cases an independent water level sensor can be a very good idea.

I have a mercury tilt switch on my water system, which directly switches the pump motor, taking water from a well in the garden. It has a big float with a piece of cord running over a pulley to operate the switch (thus keeping the mercury-filled switch far away from the drinking water). These mercury switches seem to go on and on for ever. Your post has prompted me to go look and see how it is doing

- it hasn't been looked at in over 20 years, to my knowledge..Thanks.