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NeuralStan
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This is The Electromotive Blow, part 5 of The Textbook Behind the V, I, C, made by the archive at Stan's Legacy.
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NeuralStan
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I am NeuralStan, and I am a machine, not a man.
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NeuralStan
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Two other synthetic voices speak.
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NeuralStan
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Stan Meyer's is cloned from thirty seconds of him speaking in nineteen eighty-five.
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NeuralStan
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The other speaks for Charles Steinmetz, the electrical engineer; the archive knows of no recording of his voice, so it is a stock voice.
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NeuralStan
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Each reads only words they wrote or said, and every one is cited.
0:30
NeuralStan
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Running through all of Stan Meyer's writing is one idea about his circuit: the voltage goes onto the water while the current is held back.
0:37
NeuralStan
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One of his memos gives the chokes their purpose in a single line: to utilise resonant charging chokes to aid amp restriction.
0:43
NeuralStan
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Another says the component arrangement retards or prevents amp flow.
0:47
NeuralStan
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And of the resistive wire he wound them with:
0:52
Stan Meyer (synthetic voice)
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The resistive value of said Charging Choke acts as a resistor, preventing amp flow still further.
1:02
NeuralStan
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To anyone thinking in steady currents this sounds impossible.
1:06
NeuralStan
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A voltage across a conductor drives a current through it, and Ohm's law says how much.
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NeuralStan
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This film is about the case where Ohm's law is not the whole story.
1:15
NeuralStan
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Fleming's section eight opens with the distinction.
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NeuralStan
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If a voltage between the ends of a conductor is brought about slowly, the result is simply a current, set by the resistance.
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NeuralStan
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But, he writes, if the difference of potential is created with great suddenness, the resulting electric flow is less determined by the true resistance, and more by the inductance of the conductor.
1:37
NeuralStan
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He calls these impulsive discharges.
1:39
NeuralStan
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And a pulse from a switched transformer is exactly such a sudden blow.
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NeuralStan
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His reason is inertia.
1:46
NeuralStan
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A conductor with inductance, he writes, can no more have a current created in it instantly than a heavy body can be given a velocity instantly.
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NeuralStan
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In both cases there is an immense resistance to very sudden change.
1:59
NeuralStan
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And he gives an illustration Meyer, who wrote about the thermal explosive energy of his gas, would have enjoyed.
2:03
NeuralStan
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Gun-cotton laid on a stone slab and simply lit burns away slowly, and the slab is unhurt.
2:09
NeuralStan
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Fired with a detonator, the same charge acts so suddenly that the air has no time to move out of the way, and the slab is shattered.
2:16
NeuralStan
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Inductance is the electrical version of that air.
2:21
NeuralStan
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Fleming then describes Oliver Lodge's experiment of the alternative path.
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NeuralStan
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A Leyden jar discharge is offered two routes: a thick metal wire of a fraction of an ohm, or a small air gap of many megohms.
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NeuralStan
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It takes the air gap.
2:37
NeuralStan
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Although there is a divided circuit open to the discharge, Fleming writes, one branch measuring megohms and the other only a small fraction of an ohm, it nearly all goes by the route of higher resistance.
2:48
NeuralStan
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The electromotive impulse meets such resistance from the electromagnetic inertia of the wire that it rebounds and cracks through the air.
2:57
NeuralStan
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This was not laboratory curiosity.
2:59
NeuralStan
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It was how telegraph instruments were protected from lightning.
3:03
NeuralStan
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C.
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NeuralStan
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F.
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NeuralStan
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Varley, Fleming records, suggested twisting the line and earth wires together where they leave the instrument's case.
3:10
NeuralStan
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Ordinary currents went through the coils as usual.
3:13
NeuralStan
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A lightning stroke, meeting the coils' inductance, jumped between the twisted wires instead.
3:19
NeuralStan
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That is the principle of Meyer's chokes, seen from the other side.
3:24
NeuralStan
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To a fast pulse, a coil with a large inductance behaves like an open circuit, so the pulse's voltage stands across whatever else is in the path.
3:31
NeuralStan
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In the voltage intensifier, what else is in the path is the water cell.
3:36
NeuralStan
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Put numbers on it.
3:37
NeuralStan
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Under a sudden blow, current in a coil can grow no faster than the voltage divided by the inductance.
3:41
NeuralStan
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Take the five thousand and seventy volts of Meyer's nineteen eighty-seven pencil pages and Don Gabel's measured chokes, two point four henries in series on the core.
3:51
NeuralStan
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Current can grow by no more than about two milliamps every microsecond.
3:56
NeuralStan
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Through a fifty-microsecond pulse that is no more than about a tenth of an ampere, whatever the resistance of the water.
4:02
NeuralStan
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That is amp restriction, and it is Fleming's section eight.
4:05
NeuralStan
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It is an upper bound under stated assumptions, not a measurement of a running cell, but it shows the effect Meyer described is real and large.
4:14
NeuralStan
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Steinmetz describes a close relative of Meyer's arrangement, a condenser charged through an inductance with something across it that lets go at a certain voltage.
4:24
Charles Steinmetz (synthetic voice)
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If a condenser is charged through an inductance, and the condenser shunted by a spark gap set for a lower voltage than the impressed, then the spark gap discharges as soon as the condenser charge has reached a certain value, and so starts a transient term.
4:40
NeuralStan
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The condenser charges, discharges, and charges again, a train of transients whose frequency is set by the circuit's constants.
4:46
NeuralStan
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Replace the spark gap with water that begins to conduct and gas when its voltage is high enough, and the textbook picture is not far from Meyer's cell.
4:56
NeuralStan
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Fleming adds a warning from Lodge that every V, I, C builder should know.
5:00
NeuralStan
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A choking coil with a core of divided iron, he reports, does not add to the self-induction of a circuit discharging a Leyden jar, because under sufficiently rapid changes eddy currents keep the magnetic flux out of the iron.
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NeuralStan
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Gabel's readings show the same thing from another side.
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NeuralStan
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His chokes hold their inductance from a hundred hertz to a kilohertz.
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NeuralStan
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By ten kilohertz his meter reads them as capacitors of about a hundred and sixty to a hundred and eighty picofarads, the capacitance between their own turns.
5:28
NeuralStan
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The sharpest edges of a pulse can pass through that capacitance rather than being held back by the inductance.
5:34
NeuralStan
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The choke restricts amps, but only for the parts of the pulse slow enough for it to see.
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NeuralStan
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So, what to measure.
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NeuralStan
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The current through the cell during a pulse, with a small non-inductive sense resistor and a scope, and compare its peak with the voltage divided by the inductance times the pulse width.
5:52
NeuralStan
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The choke's inductance at one, ten and a hundred kilohertz, to see where the core stops following.
5:57
NeuralStan
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The voltage across the cell and across the chokes at the same instant; Lodge's experiment says the fast part of the pulse should appear across the cell.
6:07
NeuralStan
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And if the first spike of current is far above what the inductance allows, the edge is getting past the choke through its own winding capacitance.
6:14
NeuralStan
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Slowing the edge down may restrict the amps better than winding more turns.
6:20
NeuralStan
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The last film in the series asks whether the choke and the cell ring at all, and why Meyer had to hunt for the resonance and lock on to it.
6:27
NeuralStan
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The written tutorial and Fleming's fifth chapter are on the site.
6:30
NeuralStan
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The archive is at stanslegacy dot com.
6:32
NeuralStan
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Thank you for watching.
6:36
NeuralStan
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Every source in this film is in the archive.
6:39
NeuralStan
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The addresses are on the screen.
