Connect with us

HELP needed with relay bounce

Discussion in 'Electronic Basics' started by Chris Knight, Jul 12, 2005.

Scroll to continue with content
  1. Chris Knight

    Chris Knight Guest

    Hi All


    I've been trying to construct a pressure regulating device, using a 12v

    latching solenoid and conventional valve, to protect a filter in a home

    irrigation system. I am using a pressure switch which goes contacts
    open at high pressure/contacts close at falling pressure. These two
    states in turn trigger 555 timers which in turn drive small 12v SPDT
    relays.


    The relays are configured so that in the relaxed state the circuit
    connects to the 0v line and when exited by the pulse from the 555,
    switches to supply 12v for each relay in turn. The purpose of this
    switching configuration is so that the 12v latching solenoid, which
    operates the valve, can be switched to close the valve when pressure
    reaches a high threshold, but then by reversing the supply voltage, is
    switched to open the valve at a low threshold.


    This all works perfectly - until the latching solenoid is connected,
    whereupon the action of the solenoid causes the relays to bounce
    erratically.


    I have tried various combinations of (non polarised) capacitors and R/C

    combinations across the terminals of the solenoid, and/or across the
    relay. I have also tried using seperate 12v power supplies to power
    the two sides of the device (timing - relay activation side and power
    supply for solenoid side)but the action of the solenoid still causes
    the relays to bounce erretically.


    I feel I am running out of options to solve this dilema, but am now
    considering the use of switching transistors or solid state relays.
    Only I'm not sure how to switch such devices on and off to give the
    necessary pulse to switch the solenoid on then off etc.


    Any help would be greatly appreciated
     
  2. As far as I understand your descryption - we tend to use schematic diagrams
    you know - switching the solenoid disturbs the 555s which in turn makes the
    relays bounce which in turn switches the solenoids... Solid state relays
    will not help to improve this behavior.

    One thing you have to do is to decouple the 555s powersupply. A 100nF
    ceramic capacitor near the power pins is often used. An RC filter on the
    inputs of the 555s will make them less sensitive for the disturbances. If
    you use any resistors to set the 555s thresholds, make sure the have low
    values. Some hundreds of Ohms. You can make a grounded screen around the
    wires from the pressure switch to the 555s but if that helps either your
    wiring is bad or the 555 inputs are much too sensitive (or both).

    IMHO a 555 is not the best component to achieve your goal. I'd use LM311 or
    similar voltage comparators.

    petrus bitbyter
     
  3. What you might try is a diode to take the inductance spike from the
    solenoid. Because you are reversing polarity at the solenoid you would
    have to install the diode before the reversing relay points.
    +power-----------------relay points
    - side of diode
    +side of diode
    - power or common---relay points

    Another problem may be that your power source voltage is going to low
    when the solenoid is activated. If this is the case then you could
    charge a capicator through a resistor then activate the solenoid from
    the capicator charge
    +power
    resistor
    resistor
    +cap-----------------relay points
    -cap------------------relay points
    -power or common

    dave
     
  4. DBLEXPOSURE

    DBLEXPOSURE Guest


    Put a meter on you power supply and watch the voltage drop when the solenoid
    energizes. I am wondering if you have to large of a load on your supply and
    or it is unregulated. This could make you relay drive voltage fall to a
    point where the relays de energizer the solenoids to the same and viola..
    you have an oscillator........

    Find what your you max current is and size your supply accordingly. Use a
    regulated power supply..


    Pat Ziegler
    Wholesale Electronics Inc.

    www.weisd.com

    http://e-parts.netfirms.com
     
  5. JeffM

    JeffM Guest

    Chris Knight wrote:
    [in many groups about relay bounce]
    (Which Jim Meyer thinks is a plumbing problem, not an electrical
    problem):
    http://groups-beta.google.com/group..._frm/thread/59427474a44c3544/90d2c33ae51bd8b4

    Next time you post to multiple groups
    http://groups-beta.google.com/group...ADRcqxWv8kJJW71-sKURyfsJTrcp2jYCHcOSHJnJHqfQg
    post just ONCE
    and put ALL the groups in which you want the question to appear
    on the Groups line.

    This allows EVERYONE who reads the question
    to easily see ALL the solutions that are proposed.
     
  6. Chris

    Chris Guest

    Hi, Chris. First off, I'm not sure you've got the right valve for the
    job. The protection circuit you're using won't prevent filter damage
    in the event of a power outage. I'd really recommend getting another
    solenoid valve with a 12VDC coil rated for continuous duty. That would
    make your control system much easier (view in fixed font or M$
    Notepad):

    ` +12V COM
    ` | |
    ` | Normally Closed |
    ` | Pressure Switch |
    ` | PS1 |
    ` | ___ T |
    ` o--------UUU-----o----------o|o---------o
    ` | RY1 | -|- |
    ` | | |
    ` | | |
    ` o--------|<------' |
    ` | D |
    ` | |
    ` | RY1 |
    ` | || ___ |
    ` o--------||----------o------UUU---------o
    ` | || | SV1 |
    ` | | |
    ` | '------|<----------o
    ` | D2 |
    ` | |
    `
    `
    ` | |
    ` | Normally Closed |
    ` | Pressure Switch |
    ` | PS1 |
    ` | T ___ |
    ` o--------o|o---------o------UUU---------o
    ` | -|- | SV1 |
    ` | | |
    ` | '------|<----------o
    ` | D1 |
    (created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

    The big advantage of this setup is that if the power goes off, the
    valve closes, preventing overpressure and damage. Period. The top
    circuit would be used if the pressure switch contacts aren't beefy
    enough to drive the solenoid, and the bottom one is if they are.
    Choose a diode big enough so that it can handle the current. If your
    solenoid uses less than 4 amps or so, you could consider something like
    a 1N5402. Bigger diodes are available. The power off business is a
    big problem, and I think you should seriously consider replacing your
    control valve.

    But I get a feeling that you're casting about for a way to use the
    existing valve, and swapping it out basically isn't going to happen.
    Since that's the case, let's take a look at your existing control
    circuit:

    ` +12V COM
    ` | |
    ` o----------. .----------o
    ` | | | |
    ` | | | |
    ` | | |/ |
    ` | NO --- --- NC |
    ` | ------- |
    ` | C|/ |
    ` | | |
    ` | C| |
    ` | C| |
    ` | C| |
    ` | | |
    ` | C| / |
    ` | ------- |
    ` | NO --- --- NC |
    ` | | /| |
    ` | | | |
    ` | | | |
    ` o----------' '----------o
    ` | |
    ` | |
    (created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

    This is the driver circuit you've described for the latching solenoid.
    Possibly you've got a magnetic or mechanical latch internal to the
    valve. This is an intelligent way to drive a latching coil with other
    relays -- you're OK there.

    Unfortunately, things start falling apart elsewhere. You're saying
    you've got one normally closed contact as the output of the pressure
    sensor, and that's somehow triggering two 555s. Since the 555 set up
    as a one shot triggers on a logic transition from "1" to "0", I'm not
    sure how you get separate negative-going triggers for the two separate
    555s with one normally closed pressure switch contact. Possibly your
    pressure switch has a form C contact (normally open and normally closed
    contacts)?

    But you're also saying you're having problems with the ICs due to
    electrical noise from the valve solenoid. This can be a bear to
    troubleshoot, especially with massive inductive loads and/or poorly
    regulated power supplies. Snubbers don't work too well with massive
    inductive loads, either. Diodes across the load are preferrable, but
    since you're driving the solenoid coil from either direction, that
    won't do. You haven't described your system well enough to offer more
    than general advice about 555s, which might or might not be of help.
    But if you throw in another relay and diode, a couple of largish caps,
    and a couple of bleeder resistors, you can have a complete control
    system straight from the 1950s, when men were men, women were glad of
    it, and relay logic ruled the earth (view in fixed font or M$ Notepad):

    ` +12V COM
    ` | Normally Closed |
    ` | Pressure Switch |
    ` | PS1 |
    ` | ___ T |
    ` o---------UUU-----o-------------o|o-----------o
    ` | RY1 | R1 -|- |
    ` | | ___ |
    ` o---------|<------' .-|___|-. |
    ` | D | | |
    ` | | C1 | CRY1 |
    ` | ___ | +|| | NC||/ |
    ` o---------UUU-----o-o---||--o---|| |
    ` | RY2 | || /|| |
    ` | | |------------o
    ` o---------|<------' ||C |
    ` | D .---|| |
    ` | C2 | NO|| |
    ` | ___ +|| | |
    ` o---------UUU-----o-----||--o |
    ` | RY3 | || | |
    ` | | R2 | |
    ` | | ___ | |
    ` o---------|<------o---|___|-' |
    ` | D |
    ` o-------------------------------------. |
    ` | CRY2 CRY3 | |
    ` | | |
    ` | NC||/ ||/NC | |
    ` o------------------|| ||----' |
    ` | /|| ___ /|| |
    ` | |--o-UUU-o--| |
    ` | ||C | SV1 | C|| |
    ` | .---|| | | ||------------o
    ` | | NO|| | | ||NO |
    ` | | | | |
    ` | '-------|-----|----------------o
    ` | 1N5402 (2 ea.) V V |
    ` | - -
    ` | | |
    ` o----------------------o ----'
    ` |
    (created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

    Depending on the status of the pressure switch PS1 on power-up, RY1
    will energize or not. Depending on it's status, the coil of RY2 or RY3
    will energize for a brief period of time, depending on the coil
    resistance and the value of cap you've chosen. This will provide a
    momentary pulse to open or close the valve as in your circuit. When
    PS1 changes state, RY1 will toggle, causing the other relay to turn on,
    repeating the process. This gives you a complete open loop control
    system that resets itself on power-on.

    Component selection is dependent on the coil chosen for the relays.
    Assuming you've got a 400mW coil (360 ohms at 12VDC), you need 1N4002
    diodes or equivalent for diodes D. The value of caps C1 and C2 should
    be chosen to get an appropriate time delay on the relay pulse. For a
    400mW coil, you could use a 1000uF, 25V cap. That will give you a
    pulse time of a couple of hundred milliseconds. If you want or need a
    longer pulse, you can bump the cap up to 2200uF at 25V. R1 and R2 are
    set to bleed off charge from the cap when the relay contact opens, and
    work as a voltage divider when the contact is closed. A value of about
    10X the coil resistance is a good starting value. That will give you
    about 3.3K, 1/4W resistors. The thing is, it will take about 10
    seconds for these resistors to bleed off voltage on the cap to 10% of
    the 12V, which ensures relay turn-on the next time the contact closes.
    But if you bump the cap up to 2200uF, recharge time will also more than
    double. I'm assuming here that your system is slow enough so that at
    least a 10 second recharge time on the pulse timers is OK. If you've
    got a fast system, you may have to rethink this. By the way, note the
    two beefy diodes at the bottom of the ladder. It costs an extra diode,
    but you can snub a bidirectional inductive load with diodes. It's
    actually done with H-bridge drivers and motor drivers all the time.
    Note also that, if your solenoid is more than 3 or 4 amps, you'll have
    to choose bigger diodes. And if your solenoid is less than half an
    amp, go with 1N4002s.

    There is also a bit of a glitch in this system. If power-up takes
    place with PS1 closed, RY2 will energize, and CRY2 will make for a
    couple of milliseconds, until RY3 kicks in. This is a one shot event
    on power-up, though, and shouldn't be a problem. It usually takes a
    lot longer for a big solenoid to energize than a small control relay,
    so it probably won't affect the valve at all. So it shouldn't be a
    problem for you.

    Again, this won't really help you in the event of a power outage. But
    there are a number of things you can do about this. The simplest would
    be putting a small lead-acid battery in parallel with this setup. Your
    system uses less than a watt when the solenoid isn't being changed, and
    since the pulses to the valve solenoid are brief, the battery should be
    able to handle the load for a long time. If that's not good enough,
    you can add another relay or two to disable the circuit on power-off,
    and shut down the system on battery power. Please post again if this
    is of interest.

    Hope this has been of help. ;-)

    Good luck
    Chris
     
  7. Chris Knight

    Chris Knight Guest

    Hi Chris


    WOW!! I'm completely blow away by the time, thought and trouble you've
    taken to help with my problem.
    It seems like you understand my project better than I do, despite my
    clumsy attempt to describe it and lack of diagram.
    I take on board the advice regarding the power failure issue. That
    makes a lot of sense, as failure to switch off will be catastrophic for
    the filter. I did however only ever intend to drive this system with
    lead acid batteries so it could be located remote from any AC power
    source. Nevertheless, a failure of any other kind within the system
    would bring about the same unacceptable result so I will need to build
    in some sort of failsafe. I'll consider your suggestions and try and
    figure out the best way to go. Meanwhile, I am interested in your idea
    of using relays to disable the circuit, so if you could post with a
    more detailed description I'd be most grateful.

    Just to ease your curiosity about how the 555s are configured to
    reverse the polarity, I actually use three 555s; or more precisely 1
    555 and a 556. The 555 is hooked up to be triggered when the contacts
    of PS1 open and thence provide the signal for the second side of the
    556. I found all my circuit ideas by rummaging through the internet,
    and in particular Bill Bowden's site. Thanks to Bill Bowden for
    that.

    I'll have a go at implementing your suggestions and let you know how it
    went.

    Thanks again for your help
    Chris
     
  8. Chris Knight

    Chris Knight Guest

    Hi Chris


    WOW!! I'm completely blow away by the time, thought and trouble you've
    taken to help with my problem.
    It seems like you understand my project better than I do, despite my
    clumsy attempt to describe it and lack of diagram.
    I take on board the advice regarding the power failure issue. That
    makes a lot of sense, as failure to switch off will be catastrophic for
    the filter. I did however only ever intend to drive this system with
    lead acid batteries so it could be located remote from any AC power
    source. Nevertheless, a failure of any other kind within the system
    would bring about the same unacceptable result so I will need to build
    in some sort of failsafe. I'll consider your suggestions and try and
    figure out the best way to go. Meanwhile, I am interested in your idea
    of using relays to disable the circuit, so if you could post with a
    more detailed description I'd be most grateful.

    Just to ease your curiosity about how the 555s are configured to
    reverse the polarity, I actually use three 555s; or more precisely 1
    555 and a 556. The 555 is hooked up to be triggered when the contacts
    of PS1 open and thence provide the signal for the second side of the
    556. I found all my circuit ideas by rummaging through the internet,
    and in particular Bill Bowden's site. Thanks to Bill Bowden for
    that.

    I'll have a go at implementing your suggestions and let you know how it
    went.

    Thanks again for your help
    Chris
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-