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Solenoids remaining on.

Discussion in 'Hobby Electronics' started by [email protected], Mar 16, 2007.

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  1. Guest

    Hi

    Could it cause a problem if a solenoid like the one below is left on
    for several hours or a day? I am trying to invent something where it
    supposed to only remain on for a few seconds. However, there is always
    a chance that the prototype could fail and that it may remain on.
    Could this possibly damage the solenoid or worse still cause fire?

    The solenoid I am using is at can be seen by going to http://www.jaycar.com.au
    and enterering CAT. NO. SS0901

    A description is also below. However the Jaycar site has a photo and
    more information.
    ..
    Miniature 12V Solenoid

    Square frame unit, Pull type.- Coil resistance 58- 25 watt (maximum).-
    Pulling force 100- 600g (25% duty cycle).- Stroke 1.0 - 5.5mm (25%
    duty cycle).- Total weight 46g, plunger weight 9g.- Full data supplied
    with unit.

    Your help is appreciated,
    Regards Richard.
     
  2. You have the datasheet already, haven't you? I got it right from the site
    you mentioned. Take some time to read it carefully and you'll have the
    answer.

    petrus bitbyter
     
  3. Guest

    Hi

    Thank you for your letter. I just read http://www.jaycar.com.au/products_uploaded/SS0901.pdf

    I am not fully sure what the percentages are referring to, however it
    appears to indicate the ratio of on time to the total time and that it
    would be ok if it is on continuously. However, there would be a limit
    if it is going on an off frequently. Is that correct?

    The circuit I am using is not a good connection as it is a pressure
    plate designed to measure very light weights that vary. So it could be
    possible that the circuit is complete and open intermittently, however
    the high resistance in the connection may mean that there is often
    less than 12 volts across the solenoid. So it would be hard to know
    percentages of on time.

    What is the worst thing that could happen and what is the likelihood
    that the solenoid would remain working ok if it was on for an extended
    period and intermittently off like described above?

    Your help is appreciated,
    Regards Richard.
     
  4. Wrong, you did not see the datasheet at all or could not read it. It says:
    Duty cycle 100% (continuous), max. on time infinite, power dissipated 2.5W
    at 20C, ampere turns 389 at 20C, voltage 12V. The other colums show the
    reduction of the values at higher voltages. You can drive this thing with
    38V if you need to but only with a duty cycle of 10% max. and an on time of
    7s max. As with all electronics you'll have to make sure the components can
    get rid of the heat they dissipate. That's why most PCs have those noisy
    vents.

    Meanwhile that's not to say it will be wise to keep the solenoid on if you
    don't need to. Components don't like to be driven to their limits.
    Datasheets can be conservative but some others are - let's say - too
    optimistic. But there should be no reason to find a solenoid like this fried
    when it has been on for some hours. If you nevertheless want some extra
    safety, lower the voltage (and hence the power dissipation) by one or two
    series diodes.

    petrus bitbyter
     
  5. The solenoid has a duty cycle of 25%. which means it is only rated to be
    energised for 25% of the time. The off time is needed for cool down.
    A lower supply voltage may allow that time to be extended, but it is
    hard to say.
    The worst thing that can happen is that you will cook the solenoid.
    Bottom line, use it in your application and keep an eye the solenoid for
    a few hours. you might be able to determine if it will survive or fail.
     
  6. Guest

    Hi

    Thank you for your letter.

    I probably should have also stated that for this application there
    will be nothing trying to pull the solenoid plunger out while the
    solenoid is on. It simply is to retract and allow a container to drop
    down. Does everyone who read this now agree that this would definitely
    be fine if it was on all the time for this application?

    Your help is appreciated,
    Regards Richard.
     
  7. Guest

    Hi

    Thank you for your letter.

    It looks like the solenoid should work for that project then if it
    remained on all the time.

    However, I had ideas for another project where a similar but larger
    solenoid could be used to pull a vent or louver closed when the sun is
    shining on a light sensor. It would be good to keep the sun out of the
    window for a couple of hours in the afternoon. Also another sensor
    could allow the solenoid to turn on when rain is hitting the window so
    that the louver would close.

    If I use a solenoid for this purpose it would be pulling a force
    continuously for several hours. I thought that I read that the
    solenoids may burn out if there is a force on them when they are left
    on. Will this probably be a problem if 12 volts is used or could this
    work? If it will work for some force, what force could a similar
    solenoid exert continuously?

    Another option would be using a motor to reverse like explained in an
    earlier thread that I discussed at
    http://groups.google.com/group/aus.electronics/browse_frm/thread/ae720342f1c3824c?hl=en
    It had the subject of "Motors controlling vents etc."
    However, this would be more complicated to do and I am not experienced
    in making up electronics. Do you know anyone who could help me do
    this?

    Your help is appreciated,
    Regards Richard.
     
  8. Guest

    Hi

    Thank you for your letter.

    I am from Tolga, on the Atherton Tableland behind Innisfail which is
    about to have the anniversary of Cyclone Larry that devastated our
    region.

    Where can I get a servo motor? I am about to make an order from
    Electus Distribution or Jaycar so please let me know if they have any.

    How much money could it cost to make an automatic vent like described?

    What is your email address? Mine is on my websites linked to
    http://www.advantagein.com/overview.htm

    Your help is appreciated,
    Regards Richard.
     
  9. Mike

    Mike Guest

    Saw a few other posts but if you want a simple circuit to ensure the
    solenoid *cant* stay on, yet be on for long enough to drop some plate
    then just put a large capacitor in series with the solenoid and a
    resistor in parallel with the capacitor.

    Cap something like 10,000uF or more (electrolytic)
    Resistor depends on T=RC (close enough)
    Diode across solenoid coil pointing opposite to curent flow.

    This way if the transistor (or whatever you have driving the solenoid) fails
    for whatever reason then the solenoid will eventually pull out and go off.
    Depends on the coil resistance and size of capacitor :)

    --
    Regards
    Mike
    * VK/VL Commodore FuseRails that wont warp or melt with fuse failure indication
    and now with auto 10-15 min timer for engine illumination option.
    * VN, VP, VR Models with relay holder in progress.
    * Twin Tyres to suit most sedans, trikes and motorcycle sidecars
    http://niche.iinet.net.au
     
  10. Mike

    Mike Guest


    Dont need a servo unless you want proportional response.

    A simple flip flop arrangement with two solenoids or if you can balance
    weights then just use one, dead easy, useful to learn about springs too...


    --
    Regards
    Mike
    * VK/VL Commodore FuseRails that wont warp or melt with fuse failure indication
    and now with auto 10-15 min timer for engine illumination option.
    * VN, VP, VR Models with relay holder in progress.
    * Twin Tyres to suit most sedans, trikes and motorcycle sidecars
    http://niche.iinet.net.au
     
  11. Guest

    Hi

    Thank you for your letter.

    I have been posting messages to the newsgroup by using the form at
    http://groups.google.com/group/aus.electronics

    The small solenoid may not have enough range so I may have to go to a
    bigger one detailed below. I never saw any link to a pdf file on the
    Jaycar site.

    CAT. NO. SS0902

    Standard 12V Solenoid

    Regular size square frame unit, Pull type, solder tip.- Coil
    resistance 24- 50 watt (maximum).- Pulling force 200g- 2Kg (25% duty
    cycle).- Stroke 2.0 - 12mm (25% duty cycle).- Total weight 205g,
    plunger weight 39g.- Full data supplied with unit.

    Do you think that solenoid should be similar where it can be left on
    continuously if 12 volts is used and no force? Do you think it could
    still work continuously if 20 volts is applied to it and there was no
    force pulling it? If this could be done I may still be able to use the
    small solenoid as a higher voltage should increase the pulling range.

    You do not have to be local to help me make anything. I mostly have
    had people not local as it is hard to find someone local who can do
    these projects in a small town like this.

    I have done little mechanically with motors and not made up circuits
    so I would need someone to do it for me. I will try and find out what
    force is required for the louver

    Your help is appreciated,
    Regards Richard.
     
  12. Guest

    Hi Mike and those interested

    Thank you for your letter.

    A solenoid would have to be fairly strong to open a louver. Do you
    have any suggestions on what solenoid would be strong for the purpose?
    I heard washing machine solenoids are strong but they require 240
    volts.

    With the idea that you had about a capacitor and resistor, I thought
    the solenoid may have less chance of going on and pulling in the first
    place if the pressure plate used as a switch is not a good contact.
    Therefore it would be less sensitive. Would that be so?


    Your help is appreciated,
    Regards Richard.
     
  13. Mike

    Mike Guest

    If the cap is large enough you will get a nice current surge to the solenoid
    and in any case if you also select a higher voltage - which you can because
    it wont stay on - then you will get an even higher surge if the power supply
    can handle it.

    Best of both worlds and *very* cheap to try.

    In fact, I might say, if you value your time, cheaper to try it than go
    through news posts after you have an idea what to do from a professional ;)


    --
    Regards
    Mike
    * VK/VL Commodore FuseRails that wont warp or melt with fuse failure indication
    and now with auto 10-15 min timer for engine illumination option.
    * VN, VP, VR Models with relay holder in progress.
    * Twin Tyres to suit most sedans, trikes and motorcycle sidecars
    http://niche.iinet.net.au
     
  14. Guest

    Hi Mike

    Thank you for your letter.

    Would it also be an idea to use the capacitor and resister like you
    described in the other project with the vent? Also do you know any
    strong solenoids that work on low voltage that would be capable of
    moving a vent or louver?

    Your help is appreciated,
    Regards Richard.
     
  15. Mike

    Mike Guest

    Probably, if you can devise, with the help of a bit of geometry and some
    balance a single solenoid "flip-flop" arrangement. So each time it activates
    it flips from one state to the other :)

    If you use the cap in series with the solenoid then you can drive it with
    a higher voltage and it will be stronger. This is ok since the cap will
    prevent it staying on.



    --
    Regards
    Mike
    * VK/VL Commodore FuseRails that wont warp or melt with fuse failure indication
    and now with auto 10-15 min timer for engine illumination option.
    * VN, VP, VR Models with relay holder in progress.
    * Twin Tyres to suit most sedans, trikes and motorcycle sidecars
    http://niche.iinet.net.au
     
  16. Ross Herbert

    Ross Herbert Guest


    I think what you need is a solenoid driver circuit which applies
    asharp "operate" pulse and then reduces the holding current to limit
    power loss and overheating of the coil.

    Here is an EDN idea which looks promising
    http://www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=11162

    You can achieve something similar by the simple expedient of
    connecting the solenoid in series with a suitable tungsten filament
    lamp. When cold the lamp filament is low resistance and doesn't
    dramatically affect the operating time but when heated the resistance
    of the filament is higher thus reducing the coil holding current
    without affecting its holding ability. This arrangment doesn't save
    any power, it simply reduces the holding current and might be okay for
    a jury rigged system.
     
  17. Hugh

    Hugh Guest

    Why not use a windscreen wiper motor/gearbox. 12 v operation, end stop
    switch already built in, probably more torque than necessary, easy to get
    and replace from motor wreckers.
     
  18. jasen

    jasen Guest

    yes, unfortunately: 25% duty cycle - means it heats up 4 times faster than
    it can cool down when operated at 12V


    It should be safe to operate it at 6V cotinuously (because at half voltage
    it uses 1/4 of the power) but

    at 6V it'll only have half the pulling force,

    would that work for you?

    You can surge it at the start with the full voltage to get a stronger pull
    at the start.

    Bye.
    Jasen
     
  19. Guest

    Hi Jason

    Thank you for your letter. It may not work at 6V as some power is
    needed.

    Is it easy enough to set up a solenoid so that there is a surge at the
    start and the voltage is much lower later? How would it be done so
    that it automatically happens every time a switch is activated?

    Some of the other messages I received on this topic indicate that
    would be fine to have the solenoid on continuously at 12 volts if
    there is no force being pulled by it. What do you think?

    Your help is appreciated,
    Regards Richard.
     
  20. Ross Herbert

    Ross Herbert Guest

    I posted a link to an EDN article under a thread started by Mike
    showing how this could be done.

    Here it is again
    http://www.elecdesign.com/Articles/Print.cfm?ArticleID=11162
     
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