Back EMF: 500V from 12V - plus "Movie effects"! скачать в хорошем качестве

Back EMF: 500V from 12V - plus "Movie effects"!

A demonstration and explanation of the back EMF produced when an inductive load or device has power suddenly disconnected. Using an old 230V to 2x 12V transformer primary as the inductor with a 12V battery supply and being switched by a relay, the contact arcing is clearly visible and the oscilloscope shows back EMF pulses in excess of 500V! I demonstrate how the excess voltage can be bypassed with a "flywheel diode" which allows the current to continue circulating until the energy is dissipated, and also the use of a voltage dependant resistor to limit the reverse voltage and dissipate the energy somewhat faster. And one somewhat spectacular effect of using back EMF to deliberately generate arcs and sparks between two pieces of steel - a round file and a screwdriver, in the demo. This gives a similar effect to what has been used in some movies to produce showers of sparks from contact between two weapons; though likely with larger inductors and higher voltages & currents, for even more dramatic effect! For that experiment, I used the two 12V windings of the same transformer in series for the inductor, with the 230V winding not connected and still powered from the 12V battery. Note that the small 12V 7AH lead acid battery is the ONLY power source used to create any of the high voltage spikes or arcs. A separate 12V bench supply was used to power the 555 circuit feeding the relay coil, when that was in use. Do not try to do any experiments such as this with mains AC or high voltage supplies. They are not needed and could be lethal! [The still and brief clip showing the sparking swords is taken from the original 1986 "Highlander" movie and used purely as a technical effect example. The owners rights are fully acknowledged]. 00:00:00 Introduction 00:03:20 Verifying battery voltage 00:03:40 Relay sparks and scope waveforms 00:05:05 Back EMF explanation 00:09:09 Expanded view of the waveforms 00:11:48 Effect of flywheel diode 00:13:12 Effect of a VDR (Voltage dependant resistor) 00:18:20 RC snubber: Strange and unexpected effects! 00:20:45 Uses for back EMF 00:21:35 Parallel between boost converter and "Ram pump" for water 00:23:20 Harmful effect on contacts etc. 00:24:50 Fun effects - electric "pyrotechnics, low current 00:28:00 [High speed mods - use the transformer secondaries] 00:29:30 Lights out; Electric "sparkler" time"