Body
Ole,
Thanks for the explanation, really explicit.
I think Hector claimed to use a capacitor with one of these and get it
to keep ringing after removing the battery to start it. I am not sure
how this could be accomplished unless he was using some energy coming
from the ground.
On 4/8/2018 5:54 PM, [email protected] [EVGRAY] wrote:
>
>
> The energy isn't OU but the voltage is being transformed.
>
> The high voltage is the flyback voltage (inductive kick back)
> generated when trying to break the current through a coil. A buzzer is
> actually a relay wired to power itself through a normally closed contact.
>
>
> Source of animation: https://wiki2.org/en/Electric_bell
>
> The inside of a buzzer:
> [Click to Close]
> Source of image:
> http://www.electrachime.net/resonator-door-chimes/confused-buzzer/
>
> The next image shows the inductive flyback voltage formed when
> disrupting the current through an inductor:
>
> /Inductive kickback: (a) Switch open. (b) Switch closed, electron
> current flows from battery through coil which has polarity matching
> battery. Magnetic field stores energy. (c) Switch open, Current still
> flows in coil due to collapsing magnetic field. Note polarity change
> on coil. (d) Coil voltage vs time.
> Source of the above image and text:
> https://www.allaboutcircuits.com/textbook/semiconductors/chpt-3/inductor-commutating-circuits/
>
> /When putting a low impedance like a diode across the inductor the
> flyback voltage is limited to the forward conduction voltage of the
> diode (voltage level d to the right). If putting a resistor in
> parallel to the coil the induced voltage is limited to the resistance
> multiplied by the current at cut off which is the voltage level (e)..
> /
> /
> When opening the switch without any snubber circuit the voltage is
> limited only by the breakdown voltage of the switch and the parasitic
> capacitance between the turns of the coil. This makes a door bell or a
> buzzer or a simple relay kick back.
>
> Because the inductive spike happens fast a wire hasn't got low enough
> impedance to short the spike. A wire connected to earth has too high
> inductance to short the spike which just follows the wire. EMC rules
> applies to dampen such spikes. This requires guiding the spike to some
> resistance that can dissipate the energy as heat or store the energy
> in a capacitor. For best result the snubber has to be placed close to
> the EMP source. This would be close to the coil by using short wires.
> If the snubber is placed across the switch the wires between the
> switch and the coil will radiate the spike through space because of
> the loop area formed. Any loops are to be avoided as they form coils
> of one turn. Remove loops by twisting the wires.
>
> A coil carrying current acts like a current source when the circuit is
> opened. The current always declines from the value it has during
> breaking the circuit. The voltage will adjust according to the
> impedance of the load and of course also to the parasitic capacitance
> of the coil.
>
> Regards
> Ole
>
>
>
> ---In [email protected], <nwootan@...> wrote :
>
>
>
>
> -------- Forwarded Message --------
> Subject: Re: [EVGRAY] buzzer OU
> Date: Sat, 7 Apr 2018 16:40:53 -0500
> From: Norman Wootan <nwootan@...> <mailto:nwootan@...>
> To: [email protected] <mailto:[email protected]>
>
>
>
> Back in the day (70s) W.W. Grainger sold these Lungren mouse trap
> buzzers in 6 or 12 VDC! Measured over 1,000 violts from these guys
> from frame ground side. Knock the crap out of you if you were earth
> grounded and held the buzzer while ir was powered up with 6VDC input!
>
>
> On 4/7/2018 2:54 PM, Mick mkjekyll@... <mailto:mkjekyll@...> [EVGRAY]
> wrote:
>
>>
>>
>> Norm,
>>
>> I found an old buzzer from the 70's in a box of junk. What did
>> you used
>> to do with these to study neutral spikes?
>>
>> Were you ever able to get one to ring continuously with the right
>> capacitor and no other input besides momentary one?
>>
>
>