C
CJT
- Jan 1, 1970
- 0
Touche. Let me alter that to say I wouldn't _unnecessarily_ put mainsFred said:
voltages down a well.
;-)
Sensing switch closure with & without power applied?
voltages down a well.
;-)
N
NSM
- Jan 1, 1970
- 0
| 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
| "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
R
Rodney Josey
- Jan 1, 1970
- 0
------------------------------------------------------------------------------------
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 (www.tech-chat.de) which
is what I generally use for posting to this N.G. - so I've split it into smaller sections.
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 | |
| | | | +---+
| '-' | |
| | +--|<---+
+-------+ | D2 |
| | |
.-. .-. |
| | R3 | |R4 |
| | | | |
'-' '-' |
+ | |
+----+----+ | +----o Gnd To Relay 3
| ~ | | |
- V | |
^ - +-------+-------+----Xa-----+--+----|----o +12V To Relay 3
DC | BR1 | | |+ + | |
+-----+ +---+ --- z | |
| | | DC --- A 12V .-. |
| V - | C2 + Zener R5| | |
| - ^ |470uF | | | |
| | ~ | |25V | '-' |
| +----+----+ | | | |
| | | | | |
+----------|----------------+-------+-Xb-Xc-+------+----+
| | |
| +-->|--+ .------.
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 www.tech-chat.de)
----------------------------------------------------------------------------------------------------
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:
+--------+ +--------+-------|<-----o +5V
| | | | Dx
| | --- |
Txfr-A | +--| --- 100n |
o | Q2 | | |
| | +->|| ___ === |
| +--+ +--|+---|___|--+ 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 FET
U1 = PICAXE-08M
Dx = IN4004
Resistors = to suit
(created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)
-----------------------------------------------------------------------------------------------------
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 www.tech-chat.de)
------------------------------------------------------------------------------------------------
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 | |
| |
| |
+----|<---+
| Ds |
| |
| |
o ===
+12V Gnd
(Relays)
(created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)
------------------------------------------------------------------------------------------------
FLEXIBILITY:
The "flexibility" I mentioned earlier: using the PICAXE micro gives you the option (with a few extra
components in the "mains" relay power supply circuit (1 x resistor, 1 x opto, 1 x MTP3055E FET)) -
to 'delay' the turn-on of the "mains" to the float switch / pump motor AFTER the float switch is
detected as 'closed'. Example: if the float switch is detected as 'open' - the water level in the
well is below the "minimum" pump activate level. When the float switch is detected as 'closed',
you may want to delay the pump turn-on to allow time for the water level to rise sufficiently to
provide a suitable pump 'head' flow. A 'delay' sequence can be programmed in the PICAXE micro to
achieve this. An additional option: extremely low power consumption from the batteries by using the
PICAXE 'sleep' function :- testing of the 'sense' loop could be done once every 1-2 minutes (should
take about 3-5 seconds for a sampling) - in between each 'test' the micro could be placed in sleep
mode - conserving power. This could give several months of use from a set of batteries.
-------------------------------------------------------------------------------------------------
OPTION: Insert the components below into the "MAINS RELAY SUPPLY CIRCUIT" above where indicated.
'Xa'
o
|
|
|
.-.
| |Rm
| |
'-' +----o 'Xc'
| |
+-------+ |
.-------. | |--+
Opto_2 < |/ | | ||<-+ Q3
O/P > -| | +--+|--+
< |> | |
(Option) > | | |
'-------' |
| |
'Xb'o---------+--------------+
(created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)
-----------------------------------------------------------------------------------------------
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
R
Rich Grise
- Jan 1, 1970
- 0
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
[0] I can't help but wondering - What's the purpose of this thing? Some
kind of fail-safe?
Thanks.
L
Lionel
- Jan 1, 1970
- 0
Kibo informs me that DaveC said:
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.
R
Rolavine
- Jan 1, 1970
- 0
Subject: Re: Sensing switch closure with & without power applied?
monitoring the switch position. Or runing an isolated voltage supply across the
switch then through the led part of an optocoupler.
Um, how about using a double pole switch and using the 2nd contact for
monitoring the switch position. Or runing an isolated voltage supply across the
switch then through the led part of an optocoupler.
R
Roger
- Jan 1, 1970
- 0
Use a double pole double throw switch, one site for the load and oneDaveC said:
side for the position.
T
**THE-RFI-EMI-GUY**
- Jan 1, 1970
- 0
I was waiting to see who would come up with this simple and obvious
solution! Good job!
--
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.
solution! Good job!
--
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.
B
budgie
- Jan 1, 1970
- 0
???????? The O/P did post "It's a float-operated microswitch in a well." This
may not exactly lend itself to that.
S
Sam Goldwasser
- Jan 1, 1970
- 0
**THE-RFI-EMI-GUY** said:
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: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html
Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.
Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.
K
Ken Smith
- Jan 1, 1970
- 0
Ok, use a SPDT switch and assume that if one set of contacts is open, the
other must be closed.
R
Rich Grise
- Jan 1, 1970
- 0
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
D
Dimitrios Tzortzakakis
- Jan 1, 1970
- 0
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?
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?
D
DaveC
- Jan 1, 1970
- 0
1 pair of wires coming up the well from the n.o. float switch. This is the
only sensor for level in the well (no other switches).
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.
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.
DaveC
[email protected]
This is an invalid return address
Please reply in the news group
S
Sam Goldwasser
- Jan 1, 1970
- 0
He'll hire you to climb down into the well!
--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html
Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.
Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.
R
Rich Grise
- Jan 1, 1970
- 0
Thanks for the update. I'm glad to hear you've got it solved.
Cheers!
Rich
D
Dimitrios Tzortzakakis
- Jan 1, 1970
- 0
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.
for control, it is usually (here) one NO and one NC.A 4 core cable to the
switch will do.
D
Dimitrios Tzortzakakis
- Jan 1, 1970
- 0
Or 380 V ac in Europe.
D
Dimitrios Tzortzakakis
- Jan 1, 1970
- 0
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 in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
Ï "Palindr?me" <[email protected]> Ýãñáøå óôï ìÞíõìá
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.
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 in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
Ï "Palindr?me" <[email protected]> Ýãñáøå óôï ìÞíõìá
DaveC said:
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.
J
John Fields
- Jan 1, 1970
- 0
---
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.
