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Effects of vibration on capacitors

Discussion in 'Electronic Components' started by David Harper, Nov 12, 2004.

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  1. David Harper

    David Harper Guest

    Does anyone know how severely vibration can affect a capacitor's
    ability to regulate voltage? (i.e. how much the voltage can deviate
    as a function of vibration) What types of caps are better at
    regulating voltage under high vibration?

    Thanks in advance!
    Dave
     
  2. Dan Major

    Dan Major Guest

    (David Harper) wrote in
    Caps and resisters should not be affected by vibration. They are
    monolythic (solid) devices. OK, "should not be affected..." up to a point.
    If you get vibration that causes g forces great enough to cause mechanical
    breakdown of the physical packaging, *then* the values will change. Other
    components, however, will be affected because they are either mechanical in
    function (crystals), or are such that the shape can be easily changed
    (coils, etc.). I suppose if the components were surface mounted on a
    circuit board that was flexible enough, and the vibrations caused the
    components to bend or otherwise change shape *then* caps and resistors
    could change value.
     
  3. Bob Stephens

    Bob Stephens Guest

    Depends on the capacitor. "Condenser" microphones convert vibration into a
    proportional voltage intentionally.


    Bob
     
  4. Leon Heller

    Leon Heller Guest

    Some ceramic capacitors exhibit a piezo-electric effect. Try putting a
    'scope across one and tapping it (the capacitor, not the 'scope).

    Leon
     
  5. Guy Macon

    Guy Macon Guest

    Capacitors don't regulate voltage. Do a Google search on "voltage
    regulators." Also. most capacitors will fail because vibration
    breaks them or the board they are on long before their electrical
    characteristics will change. (We are talking about a lot more
    vibration than you will find in a model rocket).
     
  6. I've already told you about the bad actors. But even those usually
    only cause problems in high impedance circuits (integrators, filters,
    coupling etc.) Used as power supply bypass, there are usually several
    in parallel and in parallel with a low impedance supply, so their
    small microphonic currents get absorbed across other loads. There is
    little chance that all the caps across the line would experience
    exactly the same vibration, in phase, and add. Your big problems in
    high vibration environments will be lack of physical ruggedness,
    resonance with the vibration, and lead breakage.
     
  7. David Harper

    David Harper Guest

    Yes, they are solid state devices that "assume" the distance between
    charge holders will remain constant. With vibration, if you have a
    few microns displacement between charges, that could result in a small
    voltage deviation, correct? The question I'm concerned with is "how
    much"?

    Thanks,
    Dave
     
  8. Pooh Bear

    Pooh Bear Guest

    Well, actually capacitors don't *regulate voltage* in the first place.

    The capacitance can vary with vibration - which can have implications
    depending on the circuit the capacitor is placed in. It won't have any
    effect of significance for power supply decoupling - if that's what you
    mean.

    The least affected caps are probably plastic film types.



    Graham
     
  9. In coupling high gain amplifier stages beware of microphonics using
    the wrong capacitor type.
     
  10. Ross Herbert

    Ross Herbert Guest

    You aren't really serious, - or are you?

    Let us assume you are and have a practical reason for knowing...

    You are referring to "regulating voltage" and since the main use of
    capacitor's in this role will be electrolytic types, then we can make
    general observations. Generally speaking, electro's for voltage
    smoothing/storage will have fairly large values at the appropriate
    voltage rating dependant upon the load requirements, so they are
    usually fairly bulky unless you are talking smd.

    Any device, whether passive or active has mass and where it is known
    that components will be subject to vibration, they must be adequately
    secured and prevented from movement and placing any stress on their
    mounting (pins, pads, whatever). Since the mounting part is the one
    which suffers most during vibration it will eventually fracture unless
    adequate precautions are taken when mounting. Other than the physical
    aspect of preventing any movement, all passive components will be able
    to handle extremely high g forces without any effect on their
    operational characteristics.

    In your later post in response to Dan Major you say that caps and
    resistors are "solid state devices" but this is plainly incorrect. You
    talk about about a "few microns displacement" and "charge holders" but
    these factors have abolutely nothing to do with passive components of
    the size and bulk of electrolytic caps. And due to the magnitude of
    the voltages and currents they are handling any sub-micron movement
    between the plates - (assuming that movement could in fact occur,
    which it doesn't) - would not be noticeable and would therefore have
    no effect whatsover on regulating ability.

    Are you sure you are not just trolling?
     
  11. Ross Herbert

    Ross Herbert Guest


    What? Of course they regulate voltage...

    What do you think the designers of old (and even today) used to
    maintain a stable voltage supply without using an active regulator?
    Yes, a bloody big capacitor, - and it still works surprisingly well.
     
  12. Tim Wescott

    Tim Wescott Guest

    High-dielectric constant ceramics certainly pick up vibration long
    before anything breaks, and no matter how much you scold them they do
    not stop.
     
  13. Andy

    Andy Guest

    Hello Dave,

    If you cross section a variety of capacitors of the various designs you'll
    probably find that micron scale tolerances grossly dwarfed by the distances
    between other key features (i.e. plate gaps, dielectric bulk impurities,
    etc.).

    Are you grappling with a voltage regulation problem during vibration?
    Glitches or drift? If you're are dealing with glitches, I'd suggest you
    look at your non-soldered interconnects -- Even your pins and sockets.
    Especially your pins and sockets if you've made several (de)mates. Without
    looking at your application, I'm a bit hard pressed to guess why you may be
    seeing voltage drift during vibration although spooky ideas such as stray
    coupling comes to mind.

    Do we get anymore clues?

    Best,
    Andy
     
  14. David Harper

    David Harper Guest

    The time spent under high vibration for the life of this project will
    be minutes, at most. I'm not worried about lead or solder fatigue.
    He stated they were solid state devices, so I just went along with it.
    My apologies.
    Pardon? You're stating that if you took a charged cap, changed the
    distance between the plates and measured the voltage across it while
    doing so, there'd be no change in voltage at all?
    Compare that "sub-micron" movement with the actual thickness of the
    dielectric material. It is very thin to begin with. A few microns of
    compression of the dielectric could be a small percentage of the
    thickness of the dielectric. I didn't know. THAT'S WHY I ASKED.
    You statement implies the dielectric would be infinitely hard and
    incompressable. No substance is.

    - would not be noticeable and would therefore have
    Well, I tried this for myself. Using a speaker and running several
    different frequencies through it (with the cap attached through a
    linkage 10" away), the oscope showed a clear voltage deviation. Some
    frequencies (10kHz) were worse than others (500Hz). Maybe before
    attacking someone's question, you may want to make sure you're not
    making too many assumptions.
    What about my question implied that I was looking for an argument?
    I'm not sure if you were just in a bad mood when you replied, but it
    was a civilized question, did not insult anyone, and had several
    people talk about microphonics.

    Dave
     
  15. Jamie

    Jamie Guest

    one of the places i do work for test their Mica Dips on 15G, thats a lot
    of vibration. in that test there was no notice able problems 99.99%
    of the time. now and then you may have one where the encasement does
    not fully fill the voids or a bad crimp.
     
  16. ddwyer

    ddwyer Guest

    In coupling high gain amplifier stages beware of microphonics using
    Hi K ceramics are piezoelectric due to barium titanate? doping.
    Hi the with a pulse and they can be heard to click.
    By reciprocality they are excellent high freq microphones.
    Hence use low k , electrolytic or plastic film for low noise.
     
  17. The only porovblem then becomes how to tell a hi K from a Low K. Like,
    they con't come labeled as to that factor.

    I suppose you could put them into a high gain amp circuit and plink on
    them and see if they put out something. But then that's too easy, isn't
    it.


     
  18. ....that everyone who replied to this question actually GAVE AN ANSWER!!!!! WHAT??!! No
    politics, backstabbing or threats of prison sex?!

    Huh, PHIL??!! :)>
     
  19. Replied to what question? You began a new thread, there is no question.
     
  20. Terry Given

    Terry Given Guest

    Yet another reason to avoid the poxy things. Z5U, Y5V = shite.

    Cheers
    Terry
     
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