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Subj: Ruhmkorff Coils
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The Ruhmkorff Coil
ΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝ
An induction coil or "spark coil" (archaically known as an "inducto_
rium" or Ruhmkorff coil after Heinrich Ruhmkorff) is a type of electrical
transformer used to produce high-voltage pulses from a low-voltage direct
current (DC) supply. To create the flux changes necessary to induce voltage
in the secondary, the direct current in the primary is repeatedly interrupted
by a vibrating mechanical contact called an interrupter. Developed beginning
in 1836 by Nicholas Callan and others, the induction coil was the first type
of transformer. They were widely used in x-ray machines, spark-gap radio
transmitters, arc lighting and quack medical electrotherapy devices from the
1880s to the 1920s. Today their only use is as the ignition coils in internal
combustion engines, and in physics education to demonstrate induction.
The term 'induction coil' is also used for a coil carrying high-fre_
quency alternating current (AC), producing eddy currents to heat objects
placed in the interior of the coil, in induction heating or zone melting
equipment.
How it works.
ΔΔΔΔΔΔΔΔΔΔΔΔ
ΪΔΔΔΔΔ> <ΔΔΔΔΔΔΏ Fig 1: A schema of the induction
³ (1) ³ coil.
³ ³
³ ³ (1) Spark gap.
±±±±±±±±±±±±±±±±±±± (2) (2) Secondary winding.
³Ϋ (4) (3) Primary winding.
/ / / / / / / /(3) ³ ³ (4) Interrupter.
(6)ΝΝ/ΝΝ/ΝΝ/ΝΝ/ΝΝ/ΝΝ/ΝΝ/ΝΝ/ΝΝΝΝΝΝ ³ ³ (5) Pivots.
/ / / / / / / / ³ ³ ³ (6) Iron core.
³ ³ o o (5) (7) Main switch.
³ ±±±±±±±±±±±±±±±±±±± ³ ³ ³ (8) DC power supply.
³ ΐΔΔΔΔΔΩ ³
³ ³
³ / +³ ³ - ³
ΐΔo oΔΔΔΔΔ΄ήΔ΄ήΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΩ
(7) ³ ³ (8)
An induction coil consists of two coils of insulated copper wire wound
around a common iron core. One coil, called the primary winding, is made from
relatively few (tens or hundreds) turns of coarse wire. The other coil, the
secondary winding, typically consists of many (thousands) turns of fine wire.
An electric current is passed through the primary, creating a magnetic field.
Because of the common core, most of the primary's magnetic field couples with
the secondary winding. The primary behaves as an inductor, storing energy in
the associated magnetic field. When the primary current is suddenly inter_
rupted, the magnetic field rapidly collapses. This causes a high voltage
pulse to be developed across the secondary terminals through electromagnetic
induction. Because of the large number of turns in the secondary coil, the
secondary voltage pulse is typically many thousands of volts. This voltage is
often sufficient to cause an electric spark, to jump across an air gap sepa_
rating the secondary's output terminals. For this reason, induction coils
were called spark coils.
The size of induction coils was usually specified by the length of
spark it could produce; a '4 inch' (10 cm) induction coil was one that could
produce a 4 inch arc.
The interrupter.
ΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔ
To operate the coil continuously, the DC supply current must be broken
repeatedly to create the magnetic field changes needed for induction. Induc_
tion coils use a magnetically activated vibrating arm called an interrupter
or break to rapidly connect and break the current flowing into the primary
coil. The interrupter is mounted on the end of the coil next to the iron core.
When the power is turned on, the magnetic field of the core created by the
current flowing in the primary attracts the interrupter's iron armature atta_
ched to the springy arm, opening a pair of contacts in the primary circuit.
When the magnetic field then collapses, the arm springs away, closing the
contacts again and turning on the current again. This cycle is repeated many
times per second.
Opposite potentials are induced in the secondary when the interrupter
'breaks' the circuit and 'closes' the circuit. However, the current change in
the primary is much more abrupt when the interrupter 'breaks'. When the con_
tacts close, the current builds up slowly in the primary because the supply
voltage has a limited ability to force current through the coil's inductance.
In contrast, when the interrupter contacts open, the current falls to zero
suddenly. So the pulse of voltage induced in the secondary at 'break' is much
larger than the pulse induced at 'close', it is the 'break' that generates the
coil's high voltage output. A "snubber" capacitor of 0.5 to 15 ζF is used
across the contacts to quench the arc on the 'break', which causes much faster
switching and higher voltages. So the open circuit output waveform of an in_
duction coil is a series of alternating positive and negative pulses, but
with one polarity much larger than the other.
ΪΔΔΔΔΔ> <ΔΔΔΔΔΔΏ Fig 2: A schema of the induction
³ (1) ³ coil with the quenching cap.
³ ³
³ ³ (1) Spark gap.
±±±±±±±±±±±±±±±±±±± (2) (2) Secondary winding.
³Ϋ (4) (3) Primary winding.
/ / / / / / / /(3) ³ ³ (4) Armature.
(6)ΝΝ/ΝΝ/ΝΝ/ΝΝ/ΝΝ/ΝΝ/ΝΝ/ΝΝ/ΝΝΝΝΝΝ ³ ³ (5) Pivots.
/ / / / / / / / ³ ³ ³ (6) Iron core.
³ ³ o o (5) (7) Main switch.
³ ±±±±±±±±±±±±±±±±±±± ³ ³ ³ (8) DC power supply.
³ ΓΔΔΔΔΔΩ ³ (9) Capacitor.
³ ³ ³³ ³
³ ΐΔΔΔ΄ΓΔΔ΄
³ (9)³³ ³
³ / +³ ³ - ³
ΐΔo oΔΔΔΔΔ΄ήΔ΄ήΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΩ
(7) ³ ³ (8)
Construction details.
ΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔ
To prevent the high voltages generated in the coil from breaking down
the thin insulation and arcing between the secondary wires, the secondary
coil uses special construction so as to avoid having wires carrying large
voltage differences lying next to each other. In one widely-used technique,
the secondary coil is wound in many thin flat pancake-shaped sections (called
"pies"), connected in series. The primary coil is first wound on the iron
core, and insulated from the secondary with a thick paper or rubber coating.
Then each secondary subcoil is connected to the coil next to it, and slid
onto the iron core, insulated from adjoining coils with waxed cardboard disks.
The voltage developed in each subcoil isn't large enough to jump between the
wires in the subcoil. Large voltages are only developed across many subcoils
in series, which are too widely separated to arc over. To give the entire
coil a final insulating coating, it is immersed in melted paraffin wax or
rosin, and the air evacuated to ensure there are no air bubbles left inside,
and the paraffin allowed to solidify, so the entire coil is encased in wax.
To prevent eddy currents, which cause energy losses, the iron core is
made of a bundle of parallel iron wires, individually coated with shellac to
insulate them electrically. The eddy currents, which flow in loops in the core
perpendicular to the magnetic axis, are blocked by the layers of insulation.
The ends of the insulated primary coil often protruded several inches from
either end of the secondary coil, to prevent arcs from the secondary to the
primary or the core.
Mercury and electrolytic interrupters:
ΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔ
Although modern induction coils used for educational purposes all use
the vibrating arm 'hammer' type interrupter described above, these were in_
adequate for powering the large induction coils used in spark-gap radio trans_
mitters and x-ray machines around the turn of the 20th century. In powerful
coils the high primary current created arcs at the interrupter contacts which
quickly destroyed the contacts. Also, since each "break" produces a pulse of
voltage from the coil, the more breaks per second the greater the power out_
put. Hammer interrupters were not capable of interruption rates over 200
breaks per second, and the ones used on powerful coils were limited to 20 to
40 breaks per second.
Therefore much research went into improving interrupters, and impro_
ved designs were used in high power coils, with the hammer interrupters only
used on small coils under 8" sparks. L‚on Foucault and others developed in_
terrupters consisting of an oscillating needle dipping into and out of a
container of mercury. The mercury was covered with a layer of spirits which
extinguished the arc quickly, causing faster switching. These were often
driven by a separate electromagnet or motor, which allowed the interruption
rate and "dwell" time to be adjusted separately of the primary current.
The largest coils used either electrolytic or mercury turbine inter_
rupters. The electrolytic or Wehnelt interrupter, invented by Arthur Wehnelt
in 1899, consisted of a short platinum needle anode immersed in an electro_
lyte of dilute sulfuric acid, with the other side of the circuit connected to
a lead plate cathode. When the primary current passed through it, gas bubbles
formed on the needle which repeatedly broke the circuit. This resulted in a
primary current broken randomly at rates up to 2000 breaks per second. Mer_
cury turbine interrupters had a centrifugal pump which sprayed a stream of
liquid mercury on rotating metal contacts. They could achieve interruption
rates up to 10,000 breaks per second, and were the most widely used type of
interrupter in commercial wireless stations.
One of the largest coils ever constructed, built in 1877 by Alfred
Apps for William Spottiswoode. Wound with 280 miles of wire, could produce a
42 in. (106 cm) spark, corresponding to roughly one million volts. Powered by
30 quart size liquid batteries and a separate interrupter.
History.
ΔΔΔΔΔΔΔ
The induction coil was the first type of electrical transformer.
During its development between 1836 and the 1860s, mostly by trial and error,
researchers discovered many of the principles that governed all transformers,
such as the proportionality between turns and output voltage, and the use of
a "divided" iron core to reduce eddy current losses.
Michael Faraday discovered the principle of induction, Faraday's
induction law, in 1831 and did the first experiments with induction between
coils of wire. The induction coil was invented by the Irish scientist and
Catholic priest Nicholas Callan in 1836 at the St. Patrick's College,
Maynooth and improved by William Sturgeon and Charles Grafton Page. George
Henry Bachhoffner and Sturgeon (1837) independently discovered that a
"divided" iron core of iron wires reduced power losses. The early coils had
hand cranked interrupters, invented by Callan and Antoine Philibert Masson
(1837). The automatic 'hammer' interrupter was invented by Rev. Prof. James
William MacGauley (1838) of Dublin, Ireland, Johann Philipp Wagner (1839),
and Christian Ernst Neeff (1847). Hippolyte Fizeau (1853) introduced the use
of the quenching capacitor. Heinrich Ruhmkorff generated higher voltages by
greatly increasing the length of the secondary, in some coils using 5 or 6
miles (10 km) of wire, and produced sparks up to 16 inches. In the early
1850s, American inventor Edward Samuel Ritchie introduced the divided secon_
dary construction to improve insulation. Callan's induction coil was named an
IEEE Milestone in 2006.
Induction coils were used to provide high voltage for early gas dis_
charge and Crookes tubes and other high voltage research. They were also used
to provide entertainment (lighting Geissler tubes, for example) and to drive
small "shocking coils", Tesla coils and violet ray devices used in quack
medicine. They were used by Hertz to demonstrate the existence of electro_
magnetic waves, as predicted by James Maxwell and by Lodge and Marconi in the
first research into radio waves. Their largest industrial use was probably in
early wireless telegraphy spark-gap radio transmitters and to power early
cold cathode x-ray tubes from the 1890s to the 1920s, after which they were
supplanted in both these applications by AC transformers and vacuum tubes.
However their largest use was as the ignition coil or spark coil in the
ignition system of internal combustion engines, where they are still used,
although the interrupter contacts are now replaced by solid state switches.
A smaller version is used to trigger the flash tubes used in cameras and
strobe lights.
ΙΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝ»
Ί Compilled from Wikipedia.com . Translatted to ASCII by LW1DSE Osvaldo Ί
Ί F. Zappacosta. Barrio Garay, Almirante Brown, Buenos Aires, Argentina. Ί
Ί Made with MSDOS 7.10's Text Editor (edit.com) in my AMD's 80486. Ί
Ί May 18, 2013 Ί
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ΙΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝΝ»
Ί Osvaldo F. Zappacosta. Barrio Garay (GF05tg) Alte. Brown, Bs As, Argentina.Ί
Ί Mother UMC ζPC:AMD486@120MHz 32MbRAM HD SCSI 8.4Gb MSDOS 7.10 TSTHOST1.43C Ί
Ί 6 celdas 2V 150AH. 18 paneles solares 10W. Ί
Ί lw1dse@yahoo.com ; lw1dse@gmail.com Ί
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