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Re: relay coil inductance

Discussion in 'Electronic Design' started by life imitates life, Sep 5, 2009.

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  1. Would not the real question be why would someone concern himself with the
    solenoid inductance of a miniature relay? I could see it if it were
    huge.
     
  2. Jon Kirwan

    Jon Kirwan Guest

    Probably, Jim is designing an IC where every 'square' or 'hex' counts.
    So maybe he doesn't want to use more than he has to? Just a thought.

    Jon
     
  3. 3.3 V relay that requires a can over it due to the field it makes?

    I suppose it is possible. I doubt much field is generated though.

    The collapsing field gets pumped into the diode. One could design the
    firing circuit to "slow stop" as well. reducing any collapsing flux to
    minimal since it is created as a result of the slew rate at which it was
    collapsed.
     

  4. Turn off can be immediate. The contacts open before the solenoid
    completes opening to the gap it was at when off.
     
  5. What would a retard that replies the way you do know?
     
  6. You should not fire them directly from the chip. They should ALL
    incorporate a driver AFTER the chip for each one. Diodes have been
    placed across the coils of relays for decades. There is a reason for
    that. The diode CLAMPS current, keeping it from the driver, idiot!
    The flyback occurs at turn off, NOT turn on, idiot, and the diode is
    ONLY in play during turn off events, and is specifically for clamping
    that flyback event.
    I think you are in overkill mode.
    Likely far more than you.
    That is another one of your problems. Your capacity to make a valid
    estimation died twenty years ago, and your capacity to make one in your
    senile condition is even less than it was when you were not senile. Even
    then, it was marginal, at best.
     
  7. Relay opening time on a mechanical relay is NOT electrically related.

    It is mechanical. You can slow it down electrically, but there is
    nothing you can do that makes the event occur any faster.
     
  8. boB

    boB Guest


    Do you think that, with a diode across the relay to reduce the flyback
    voltage spike, that slow-er decaying current, and its associated
    magnetic field holding the relay in, does NOT slow down the relay
    opening ???

    boB
     
  9. The coil's flux collapses and creates a spike. The diode clamping that
    spike does NOT slow the spring loaded return time of the plate which is
    attached to the contact(s) as it pulls away from the solenoid core end
    face.

    So, the answer is NO. The magnetic field is collapsing, as in NOT
    "holding in" the relay any longer. The plate begins to pull away as soon
    as the power is removed, and the clamping diode does nothing to slow that
    process.

    The field is collapsing, not being splayed out. There is no longer an
    attachment force as soon as the power is removed. The collapsing flux
    induces a current though the diode, but that diode does NOT slow the
    collapse rate. That rate was determined by the slew rate of the voltage
    change which was full voltage to zero in a practically square wave fall
    rate.

    The collapsing flux makes the back EMF. The diode eats that current.
    The plate has already been released long before those events. Diode or
    not, the relay opens at the same rate. The diode is there to kill the
    spike, and that is all.

    To slow the process, one needs to slow the rate at which the excitation
    voltage falls. Once it falls below a certain value, however, the relay
    will STILL "snap" open, so even that method does not "slow" things much.

    Speeding one up, however, is what the engineers that designed it did.
    I doubt you will be able to improve on their works short of adding a
    solenoid to pull the relay off faster than the mechanical spring does.
    A push-pull relay where there are two solenoids operating it.

    Otherwise, you are simply tied to the mechanics of the system.
     
  10. More fucking retarded bullshit from someone with no real argument that
    is based in fact.
    No shit, you retarded ****. It was *I* that said that you can slow the
    opening, but will fail to make it faster than it already is.
    Wrong. The closure plate begins to pull away as soon as the excitation
    voltage is removed. A static field pulls in and holds the plate, a
    collapsing field does not.
    That is a function of how far BEFORE the plate closure point they MAKE
    contact. They will always make contact before the plate is fully
    clasped. They will always remain in contact as the plate pulls away,
    until it reaches a specific point of opening.
    First it has to matter. Nearly all designers remove excitation voltage
    immediately. That means the field is removed immediately. That is also
    what causes the spike.
    That is what the diode is for. There will be no current any further
    back in the circuit if the diode does its job.
     
  11. Lighting your retarded ass up with a few fibrillation inducing jolts is
    well within the realm of my knowledge, and proves yet again that you have
    no clue about that which you spew.

    Of course shit is not all that conductive, so I might have to up the
    juice quite a bit to have an effect on you.

    pasticcio
     
  12. DarkMatter

    DarkMatter Guest

    Not to mention the hard as rock heart, if there is even one there.
     
  13. amdx

    amdx Guest

    Here's a pretty good pdf with explanation of different spike suppresion
    methods.
    It lists drop out times for the different methods, for one particular relay
    and values.
    http://www.kilovac.com/appnotes/app_pdfs/13c3311.pdf
    PS. A diode is the slowest dropout time listed.
    Mike
     
  14. Note also that the diode is also the best at suppressing the spike.

    Note also that UNsupressed is the only way to get it fast. ALL the
    other methods slow it.

    ALL of the other methods violate his 'issues' list.

    In many cases, that is the most important constraint (the spike).
    Note also that all the figures are for 12V relays, which are not in much
    use on modern low voltage circuit designs these days.

    I am quite certain that any 3.3V relay you choose to examine will prove
    to be faster than any of the numbers that more than 10 year old document
    measured. Even the diode.
     
  15. DarkMatter

    DarkMatter Guest


    All the pussy that you are is doing is looking to get a rise out of me.

    That only amounted to me chuckling at the depth of your stupidity.
     
  16. amdx

    amdx Guest

    Probably this one?
    http://www.kilovac.com/appnotes/app_pdfs/13c3311.pdf
    Note, life imitates life finds no wisdom in a ten year old document.
    Mike
     
  17. John Larkin

    John Larkin Guest

    Diode+resistor or diode+zener are both a lot faster than just a diode.

    Or even just a series or shunt resistor, if you can spare the power.

    No clamp at all is even faster; just let it fly up and ring, with
    suitable precautions.

    The untimate would be to apply a large reverse voltage to the coil
    until the current goes to zero. That's what happens automagically in a
    linear amp driving an inductive load with current feedback.

    Reeds are usually pretty lossy, lots of coil resistance, so may be OK
    with just a diode. But they are terrible gadgets in general. In my
    experience, they are nowhere near as reliable as claimed, and they
    bounce/twang forever.

    John
     
  18. You cannot make it open any faster than a non-suppressed version.
     
  19. amdx

    amdx Guest

    Quote from life imitates life,
    " I am quite certain that any 3.3V relay you choose to examine will prove
    to be faster than any of the numbers that more than 10 year old document
    measured. Even the diode."

    Just doesn't seem like you saw a lot of wisdom in the 10 your old document.
    Tell me, what part of it do you think is wise?
    I didn't morph and I'm not a retard,
    I think your losing your mind.
    Mike
     
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