A
low tension coil is an electrical device used to create a spark across the points of an
ignitorIgnitor is a heavy metal band based in Austin, Texas, USA.- History :Ignitor was formed in 2003 by Erika Tandy , Stuart Laurence aka Batlord , Pat Doyle , Beverly Barrington , and Brendon Bigelow...
on early 1900s
gasolineGasoline or petrol is a petroleum-derived liquid mixture, primarily used as fuel in internal combustion engines...
engines, generally flywheel engines,
hit and miss engineA hit-and-miss engine is a type of four-stroke internal combustion engine that was conceived in the late 1800s and was produced by various companies from the 1890s through approximately the 1930s. The name comes from the method of speed control that is implemented on these engines...
s, and other engines of that era. In modern electronic terms, a low tension coil is simply a large
inductorAn inductor or a reactor is a passive electrical component that can store energy in a magnetic field created by the electric current passing through it. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
, an electrical device that stores energy for brief periods. The term "low tension" was the terminology of the day used to differentiate it from the term "high tension", and generally meant "low voltage" (tension) as opposed to "high voltage" (tension).
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A
low tension coil is an electrical device used to create a spark across the points of an
ignitorIgnitor is a heavy metal band based in Austin, Texas, USA.- History :Ignitor was formed in 2003 by Erika Tandy , Stuart Laurence aka Batlord , Pat Doyle , Beverly Barrington , and Brendon Bigelow...
on early 1900s
gasolineGasoline or petrol is a petroleum-derived liquid mixture, primarily used as fuel in internal combustion engines...
engines, generally flywheel engines,
hit and miss engineA hit-and-miss engine is a type of four-stroke internal combustion engine that was conceived in the late 1800s and was produced by various companies from the 1890s through approximately the 1930s. The name comes from the method of speed control that is implemented on these engines...
s, and other engines of that era. In modern electronic terms, a low tension coil is simply a large
inductorAn inductor or a reactor is a passive electrical component that can store energy in a magnetic field created by the electric current passing through it. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
, an electrical device that stores energy for brief periods. The term "low tension" was the terminology of the day used to differentiate it from the term "high tension", and generally meant "low voltage" (tension) as opposed to "high voltage" (tension). High tension coils produce high voltages, generally meant to produce a spark across a spark plug.
Construction
A low tension coil consists of an iron core that has wire wrapped around it. The size of the iron core, the number of turns of wire, and the size of the wire determine the electrical properties of the coil. Terminals are provided to connect the coil into the ignition circuit. The wood ends are provided for mechanical stability, to provide for the terminal placement and to hold the wire on the coil over time. A cloth or tape covering is provided to protect the windings.
Use
A low tension coil for engine ignition is used in conjunction with a battery and an ignitor. The ignitor is no more than a set of contacts that reside inside the combustion chamber of the engine. A series circuit is made between the three components: battery connects to coil, second terminal on the coil connects to the ignitor, second terminal on the ignitor (usually connected electrically and mechanically to the engine itself) connects to the second terminal of the battery.
Theory of Operation
An inductor attempts to maintain a constant current flow through it. If the current in the circuit in which the inductor is connected goes down for some reason, the voltage developed across the inductor will go up in an attempt to try to maintain the constant current. When used with an ignitor ignition system in an engine, there is current flow when the ignitor contacts are closed. When the ignitor contacts are opened by the mechanical parts of the engine, current flow is interrupted. Because the low tension coil wants to maintain that current flow, the voltage across the coil rapidly goes up (usually to several hundred volts). When the voltage rises high enough, the voltage will jump the still very small gap of the ignitor contacts and create a spark which ignites the fuel mixture in the engine. Since there is a finite amount of energy stored in the coil, as soon as the spark jumps the gap the voltage across the coil collapses. As soon as the engine rotates and the ignitor contacts again close, current starts to flow through the coil and it again stores energy for the next cycle. A good description and moving gif of a low tension coil in operation can be found on
Harrys Old Engines Ignition Page