Touche. Let me alter that to say I wouldn't _unnecessarily_ put mains voltages down a well.
;-)
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| 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.
N
------------------------------------------------------------------------------------ Hi Dave,
I think I may have come up with a circuit to meet your requirements...:).
Unfortunately it is a bit too much to acurately lay it out using AACircuit
If I'm reading what you say in your posts right - your system comprises a 120VAC submersible pump (in a well) controlled by a float switch (which is in series with the pump) - AND - you want to be able to monitor the state of the float switch - AND - set an alarm input depending on whether the switch is closed or open - IRRESPECTIVE of whether the 120VAC power is on or off ????
QUESTION: what is the max current draw of the pump motor ? If I'm correct with my summizing, then the circuit I propose would certainly perform the task plus give some added FLEXIBILITY to how you can use it. The circuit uses around
35-40 components mounted on a PCB and along with a 4 x AA NI-MH (or NICAD) batteries (1.5V ea @ 2300mAh = 6V DC) should fit into a 8"x 6"x 3" plastic enclosure case and cost approx $75.00 or less (depending on where you purchase the components).The circuit concept is: If the in-well pump is say 120VAC @ 10A then the minimum 'operating' voltage before the pump motor stalls is probably around 60VAC @ 5-6A - so at lower AC the motor doesn't turn
- however - the motor windings will still pass low voltage / low current AC (the motor just wont turn) - THUS - this effect can be used to easily determine the "state" of the in-line float switch - e.g.. if the low voltage / low current AC flows thru the motor - then the float switch is closed - if not - the float switch is open - VOILA - a method to determine the float switch "state". NOTE: this will work whether the normal AC to the pump motor is on - or - off (actually 'off' manually - or - when mains power fails due to a blackout or low power condition - brownout). NOTE: AC voltage is used instead of DC because AC motors may have internal 'capacitive' coupling as well as inductive
- DC is generally 'blocked' by such coupling methods - AC will pass thru.
A transformer-less AC-to-DC 12V DC power supply across the Mains active and neutral lines drives 2 x
10A DPDT 12vdc coil relays - 1 relay in the mains active line - 1 in the mains neutral line (ISOLATES the 'outside' well mains wires from the 'inside' well mains wires). A 3rd low power SPDT relay 12vDC coil is also operated by this power supply and is used to turn on / off the battery power to the 'control' circuit. You'll need to work out the component values to suit.--------------------------------------------------------------------------------------------- MAINS RELAY SUPPLY:
Active (outside .------. Mains Well) RLY1|--o\ |
120V o------+-------+-----------------------------------------|--o o-|--+---------o 'ACTIVE' AC | | | | | (inside + .-. +--------|--o\ | | Well) --- | | R1 | _____|_-o o-|--+ C1 --- | | | | | )| | + '-' | | _|_)| | | | | | |'------' | | | | | | .-. +---|---|--------------------o Txfr1 | | | R2 | | | | | | +---+ | '-' | | | | +--||--+ .------. 120V | | D3 | |--o\ | AC o---------------+-----------------------------------------|--o o-----+--------o 'NEUTRAL Neutral | | | | | (inside Mains | +-|-|--o\ | | Well) (outside | | |_|_-o o-|---+ Well) | | | )| | |____|___|_)| |RLY2 +----o Isense-B | '------' | | | +------------------+NOTE: Xa, Xb, Xc = OPTION
(created by AACircuit v1.28.4 beta 13/12/04
---------------------------------------------------------------------------------------------------- Whilst ever the mains is on - the relays are operated via the 12vDC - letting the mains AC thru to the float switch & pump in the well. If the mains is turned off (manually) - or
- fails (blackout), the relays de-activate. The 3rd relay turns on the 'control' circuit - when power fails (or is turned off manually).
The 'control' circuit (shown below) is formed as a battery operated low-voltage (5v DC) DC-to-AC converter providing around 15-18VAC @ 100-150mA which is coupled to the 'inside' well mains wires by a small low current step-up transformer via one pole of the each of the "isolation" relays. An PICAXE-08M microcontroller is at the heart of the converter / monitor - 2 outputs drive MTP3055E MOSFETS which switch 0v to one side of upper & lower windings (secondary) of the transformer - +5vdc is fed to the centre tap of the windings. The output winding (primary) steps up the generated voltage to around 15-18VAC @ approx 100mA. This generated AC voltage now flows
- thru the 'active' line relay - to the float switch (if closed) - thru the pump motor windings - to the 'neutral' line relay - thru a 'current' detector - back to the other side of the transformer output winding.
----------------------------------------------------------------------------------------------- CONTROL CIRCUIT:
+--------+ +--------+-------||| ___ === | | +--+ +--|+---|___|--+ 0V | +--. | | Ra | | U1 )|.---+ | | .------o-----. TXFR )|(______o +5V === | | +ve | ___ Rc )|( 0V +------oP4 P0o----|___|------o 'Alarm O/P' )|'---+ | | ___ +--' | +----------oP2 P1o----|___|---+ | +-----+ | | | Rd | | | | +----oP3 Sio--+ | o | | | | 0V | | .------. Txfr-B +--| | | '------o-----' .-. | | > (Isense-A) Q1 | | | | | | | | < Opto_2 +->|| ___ | | | | |Re | V > Led +--|+----|___|---+ | === '-' |- < (Option) | Rb | 0V | | | > | | | '------ === o === | 0V 'sense' 0V | ===
0V Q1,Q2 = MTP3055E FETU1 = PICAXE-08M
Dx = IN4004
Resistors = to suit
(created by AACircuit v1.28.4 beta 13/12/04
-----------------------------------------------------------------------------------------------------
The 'current' detector is shown below - when sufficient current flows thru the resistor Rx, the optoisolator's led turns on. The opto's output transistor turns on - pulling the 'sense' line low. THUS: if the float switch is closed - the 'sense' line is low; if the float switch is open - the 'sense' line is high.
------------------------------------------------------------------------------------------------ CURRENT SENSE DETECTOR CIRCUIT:
Txfr-B (Isense-A) o | | |~ +----------o +5V +-+-+-------|--------+ | + | | | + - V | .-. .-. ^ - .-.Rx | |47r | |1K0 Diodes | | | | | | | | - +---+ + | | '-' '-' | | '-' + + V - | | +-----+----------o Sense - ^ | .-+-------+--. | | | | V |/ | +-+-+-------+ | - -| | |~ | | | |> | OPTO_1 | | | | + | | | '-+-------|--' | | | | | +--------+ +----------------o 0V | o (Isense-B) AC Neutral via Relay
(created by AACircuit v1.28.4 beta 13/12/04
------------------------------------------------------------------------------------------------
The 'sense' line is monitored by 'IN3' pin of the PICAXE-08M chip. A 3rd 'output' of the PICAXE-08M is then used as the "alarm" drive out either via a 2nd OPTO - or - via a transistor....
------------------------------------------------------------------------------------------------ BATTERY SUPPLY:
.------. Dv +ve | /o-|---->|-------o +5V o----------------|--o o-| (control) | ____|__ | | | | )| | Rly3 --- | _|__)| | Bat - | | '------' --- | | 6V - | +------+ 2300mAh | | | NI-MH | | | o-------------------------------------o 0V -ve | | | | | | +----| | | | || Opto_2 < |/ | | || -| | +--+|--+ < |> | | (Option) > | | | '-------' | | | 'Xb'o---------+--------------+
(created by AACircuit v1.28.4 beta 13/12/04
-----------------------------------------------------------------------------------------------
The PICAXE series of chips are very easy to program and are very low in cost - MUCH BANG for little BUCKS - in such small packages.
I hope this extra long post is helpful ??
Best of luck with your project.
Oz-Rod
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.
-- W . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^---------------------------------------------------------------
Use a double pole double throw switch, one site for the load and one side for the position.
--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"
The Lost Deep Thoughts By: Jack Handey
Before a mad scientist goes mad, there's probably a time
when he's only partially mad. And this is the time when he's
going to throw his best parties.
Except that it doesn't solve the problem if he has to go down into the well and replace the switch. :)
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Important: Anyth>
???????? The O/P did post "It's a float-operated microswitch in a well." This may not exactly lend itself to that.
Ok, use a SPDT switch and assume that if one set of contacts is open, the other must be closed.
-- -- kensmith@rahul.net forging knowledge
This
He'll hire you to climb down into the well! :)
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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
to
---
10kHz IN>--[1.6nF]--+ | MAINS>--------------+--------//------------O---> | | MAINS>---------------+-------//-----[RL]---------O | 10kHz OUT>--[1.6nF]--+If you can make sure that mains hot is, and stays mains hot, then:
10kHz IN>--[1.6nF]--+ | MAINS HOT>----------+-------//------------O---> | | MAINS NEUT>---------+-------//------[RL]--------O | 10kHz OUT>----------+Even though 1.6nF looks like 1.6 megohms at 60Hz, at turn-on after a mains failure the spike getting throught the cap and into the 10kHz source might not be a good thing, so you might want to do something like this:
10kHz IN>-----+---[1.6nF]--+ | | [CR1] | |A | |K | [CR2] | | | MAINS HOT>----|------------+-------//-----------O---> | | | MAINS NEUT>---+------------+-------//------[RL]-------O | 10kHz OUT>-----------------+Where CR1 and CR2 are Zener diodes with a voltage rating slightly higher than the output voltage of the 10kHz source.
-- John Fields
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.
-- Sue
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