Body
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 https://wiki2.org/en/Electric_bell
The inside of a buzzer:
Source of image: http://www.electrachime.net/resonator-door-chimes/confused-buzzer/ 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/ 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?